- 23 Aug, 2021 40 commits
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Christian Brauner authored
Now that we converted btrfs internally to account for idmapped mounts allow the creation of idmapped mounts on by setting the FS_ALLOW_IDMAP flag. We only need to raise this flag on the btrfs_root_fs_type filesystem since btrfs_mount_root() is ultimately responsible for allocating the superblock and is called into from btrfs_mount() associated with btrfs_fs_type. The conversion of the btrfs inode operations was straightforward. Regarding btrfs specific ioctls that perform checks based on inode permissions only those have been allowed that are not filesystem wide operations and hence can be reasonably charged against a specific mount. Reviewed-by:
Josef Bacik <josef@toxicpanda.com> Signed-off-by:
Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by:
David Sterba <dsterba@suse.com> Signed-off-by:
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Christian Brauner authored
Make the ACL code idmapped mount aware. The POSIX default and POSIX access ACLs are the only ACLs other than some specific xattrs that take DAC permissions into account. On an idmapped mount they need to be translated according to the mount's userns. The main change is done to __btrfs_set_acl() which is responsible for translating POSIX ACLs to their final on-disk representation. The btrfs_init_acl() helper does not need to take the idmapped mount into account since it is called in the context of file creation operations (mknod, create, mkdir, symlink, tmpfile) and is used for btrfs_init_inode_security() to copy POSIX default and POSIX access permissions from the parent directory. These ACLs need to be inherited unmodified from the parent directory. This is identical to what we do for ext4 and xfs. Reviewed-by:
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Christian Brauner authored
The INO_LOOKUP_USER is an unprivileged version of the INO_LOOKUP ioctl and has the following restrictions. The main difference between the two is that INO_LOOKUP is filesystem wide operation wheres INO_LOOKUP_USER is scoped beneath the file descriptor passed with the ioctl. Specifically, INO_LOOKUP_USER must adhere to the following restrictions: - The caller must be privileged over each inode of each path component for the path they are trying to lookup. - The path for the subvolume the caller is trying to lookup must be reachable from the inode associated with the file descriptor passed with the ioctl. The second condition makes it possible to scope the lookup of the path to the mount identified by the file descriptor passed with the ioctl. This allows us to enable this ioctl on idmapped mounts. Specifically, this is possible because all child subvolumes of a parent subvolume are reachable when the parent subvolume is mounted. So if the user had access to open the parent subvolume or has been given the fd then they can lookup the path if they had access to it provided they were privileged over each path component. Note, the INO_LOOKUP_USER ioctl allows a user to learn the path and name of a subvolume even though they would otherwise be restricted from doing so via regular VFS-based lookup. So think about a parent subvolume with multiple child subvolumes. Someone could mount he parent subvolume and restrict access to the child subvolumes by overmounting them with empty directories. At this point the user can't traverse the child subvolumes and they can't open files in the child subvolumes. However, they can still learn the path of child subvolumes as long as they have access to the parent subvolume by using the INO_LOOKUP_USER ioctl. The underlying assumption here is that it's ok that the lookup ioctls can't really take mounts into account other than the original mount the fd belongs to during lookup. Since this assumption is baked into the original INO_LOOKUP_USER ioctl we can extend it to idmapped mounts. Reviewed-by:
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Christian Brauner authored
Setting flags on subvolumes or snapshots are core features of btrfs. The SUBVOL_SETFLAGS ioctl is especially important as it allows to make subvolumes and snapshots read-only or read-write. Allow setting flags on btrfs subvolumes and snapshots on idmapped mounts. This is a fairly straightforward operation since all the permission checking helpers are already capable of handling idmapped mounts. So we just need to pass down the mount's userns. Reviewed-by:
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Christian Brauner authored
The SET_RECEIVED_SUBVOL ioctls are used to set information about a received subvolume. Make it possible to set information about a received subvolume on idmapped mounts. This is a fairly straightforward operation since all the permission checking helpers are already capable of handling idmapped mounts. So we just need to pass down the mount's userns. Reviewed-by:
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Christian Brauner authored
So far we prevented the deletion of subvolumes and snapshots using subvolume ids possible with the BTRFS_SUBVOL_SPEC_BY_ID flag. This restriction is necessary on idmapped mounts as this allows filesystem wide subvolume and snapshot deletions and thus can escape the scope of what's exposed under the mount identified by the fd passed with the ioctl. Deletion by subvolume id works by looking for an alias of the parent of the subvolume or snapshot to be deleted. The parent alias can be anywhere in the filesystem. However, as long as the alias of the parent that is found is the same as the one identified by the file descriptor passed through the ioctl we can allow the deletion. Reviewed-by:
Qu Wenruo <wqu@suse.com> Signed-off-by:
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Christian Brauner authored
Destroying subvolumes and snapshots are important features of btrfs. Both operations are available to unprivileged users if the filesystem has been mounted with the "user_subvol_rm_allowed" mount option. Allow subvolume and snapshot deletion on idmapped mounts. This is a fairly straightforward operation since all the permission checking helpers are already capable of handling idmapped mounts. So we just need to pass down the mount's userns. Subvolumes and snapshots can either be deleted by specifying their name or - if BTRFS_IOC_SNAP_DESTROY_V2 is used - by their subvolume or snapshot id if the BTRFS_SUBVOL_SPEC_BY_ID is set. This feature is blocked on idmapped mounts as this allows filesystem wide subvolume deletions and thus can escape the scope of what's exposed under the mount identified by the fd passed with the ioctl. This means that even the root or CAP_SYS_ADMIN capable user can't delete a subvolume via BTRFS_SUBVOL_SPEC_BY_ID. This is intentional. The root user is currently already subject to permission checks in btrfs_may_delete() including whether the inode's i_uid/i_gid of the directory the subvolume is located in have a mapping in the caller's idmapping. For this to fail isn't currently possible since a btrfs filesystem can't be mounted with a non-initial idmapping but it shows that even the root user would fail to delete a subvolume if the relevant inode isn't mapped in their idmapping. The idmapped mount case is the same in principle. This isn't a huge problem a root user wanting to delete arbitrary subvolumes can just always create another (even detached) mount without an idmapping attached. In addition, we will allow BTRFS_SUBVOL_SPEC_BY_ID for cases where the subvolume to delete is directly located under inode referenced by the fd passed for the ioctl() in a follow-up commit. Here is an example where a btrfs subvolume is deleted through a subvolume mount that does not expose the subvolume to be delete but it can still be deleted by using the subvolume id: /* Compile the following program as "delete_by_spec". */ #define _GNU_SOURCE #include <fcntl.h> #include <inttypes.h> #include <linux/btrfs.h> #include <stdio.h> #include <stdlib.h> #include <sys/ioctl.h> #include <sys/stat.h> #include <sys/types.h> #include <unistd.h> static int rm_subvolume_by_id(int fd, uint64_t subvolid) { struct btrfs_ioctl_vol_args_v2 args = {}; int ret; args.flags = BTRFS_SUBVOL_SPEC_BY_ID; args.subvolid = subvolid; ret = ioctl(fd, BTRFS_IOC_SNAP_DESTROY_V2, &args); if (ret < 0) return -1; return 0; } int main(int argc, char *argv[]) { int subvolid = 0; if (argc < 3) exit(1); fprintf(stderr, "Opening %s\n", argv[1]); int fd = open(argv[1], O_CLOEXEC | O_DIRECTORY); if (fd < 0) exit(2); subvolid = atoi(argv[2]); fprintf(stderr, "Deleting subvolume with subvolid %d\n", subvolid); int ret = rm_subvolume_by_id(fd, subvolid); if (ret < 0) exit(3); exit(0); } #include <stdio.h>" #include <stdlib.h>" #include <linux/btrfs.h" truncate -s 10G btrfs.img mkfs.btrfs btrfs.img export LOOPDEV=$(sudo losetup -f --show btrfs.img) mount ${LOOPDEV} /mnt sudo chown $(id -u):$(id -g) /mnt btrfs subvolume create /mnt/A btrfs subvolume create /mnt/B/C # Get subvolume id via: sudo btrfs subvolume show /mnt/A # Save subvolid SUBVOLID=<nr> sudo umount /mnt sudo mount ${LOOPDEV} -o subvol=B/C,user_subvol_rm_allowed /mnt ./delete_by_spec /mnt ${SUBVOLID} With idmapped mounts this can potentially be used by users to delete subvolumes/snapshots they would otherwise not have access to as the idmapping would be applied to an inode that is not exposed in the mount of the subvolume. The fact that this is a filesystem wide operation suggests it might be a good idea to expose this under a separate ioctl that clearly indicates this. In essence, the file descriptor passed with the ioctl is merely used to identify the filesystem on which to operate when BTRFS_SUBVOL_SPEC_BY_ID is used. Reviewed-by: -
Christian Brauner authored
Creating subvolumes and snapshots is one of the core features of btrfs and is even available to unprivileged users. Make it possible to use subvolume and snapshot creation on idmapped mounts. This is a fairly straightforward operation since all the permission checking helpers are already capable of handling idmapped mounts. So we just need to pass down the mount's userns. Reviewed-by:
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Christian Brauner authored
When a new subvolume is created btrfs currently doesn't check whether the fsgid/fsuid of the caller actually have a mapping in the user namespace attached to the filesystem. The VFS always checks this to make sure that the caller's fsgid/fsuid can be represented on-disk. This is most relevant for filesystems that can be mounted inside user namespaces but it is in general a good hardening measure to prevent unrepresentable gid/uid from being written to disk. Since we want to support idmapped mounts for btrfs ioctls to create subvolumes in follow-up patches this becomes important since we want to make sure the fsgid/fsuid of the caller as mapped according to the idmapped mount can be represented on-disk. Simply add the missing fsuidgid_has_mapping() line from the VFS may_create() version to btrfs_may_create(). Reviewed-by:
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Christian Brauner authored
Enable btrfs_permission() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Enable btrfs_setattr() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Enable btrfs_tmpfile() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Enable btrfs_symlink() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Enable btrfs_mkdir() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Enable btrfs_create() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Enable btrfs_mknod() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Enable btrfs_getattr() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Enable btrfs_rename() to handle idmapped mounts. This is just a matter of passing down the mount's userns. Reviewed-by:
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Christian Brauner authored
Extend btrfs_new_inode() to take the idmapped mount into account when initializing a new inode. This is just a matter of passing down the mount's userns. The rest is taken care of in inode_init_owner(). This is a preliminary patch to make the individual btrfs inode operations idmapped mount aware. Reviewed-by:
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Christian Brauner authored
Various filesystems rely on the lookup_one_len() helper to lookup a single path component relative to a well-known starting point. Allow such filesystems to support idmapped mounts by adding a version of this helper to take the idmap into account when calling inode_permission(). This change is a required to let btrfs (and other filesystems) support idmapped mounts. Cc: Christoph Hellwig <hch@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: linux-fsdevel@vger.kernel.org Reviewed-by:
Christoph Hellwig <hch@lst.de> Signed-off-by:
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Anand Jain authored
Sysfs file has grown big. It takes some time to locate the correct struct attribute to add new files. Create a table and map the struct attribute to its sysfs path. Also, fix the comment about the debug sysfs path. And add the comments to the attributes instead of attribute group, where sysfs file names are defined. Signed-off-by:
Anand Jain <anand.jain@oracle.com> Reviewed-by:
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Qu Wenruo authored
[BUG] It's easy to trigger NULL pointer dereference, just by removing a non-existing device id: # mkfs.btrfs -f -m single -d single /dev/test/scratch1 \ /dev/test/scratch2 # mount /dev/test/scratch1 /mnt/btrfs # btrfs device remove 3 /mnt/btrfs Then we have the following kernel NULL pointer dereference: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 9 PID: 649 Comm: btrfs Not tainted 5.14.0-rc3-custom+ #35 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:btrfs_rm_device+0x4de/0x6b0 [btrfs] btrfs_ioctl+0x18bb/0x3190 [btrfs] ? lock_is_held_type+0xa5/0x120 ? find_held_lock.constprop.0+0x2b/0x80 ? do_user_addr_fault+0x201/0x6a0 ? lock_release+0xd2/0x2d0 ? __x64_sys_ioctl+0x83/0xb0 __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae [CAUSE] Commit a27a94c2 ("btrfs: Make btrfs_find_device_by_devspec return btrfs_device directly") moves the "missing" device path check into btrfs_rm_device(). But btrfs_rm_device() itself can have case where it only receives @devid, with NULL as @device_path. In that case, calling strcmp() on NULL will trigger the NULL pointer dereference. Before that commit, we handle the "missing" case inside btrfs_find_device_by_devspec(), which will not check @device_path at all if @devid is provided, thus no way to trigger the bug. [FIX] Before calling strcmp(), also make sure @device_path is not NULL. Fixes: a27a94c2 ("btrfs: Make btrfs_find_device_by_devspec return btrfs_device directly") CC: stable@vger.kernel.org # 5.4+ Reported-by:
butt3rflyh4ck <butterflyhuangxx@gmail.com> Reviewed-by:
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Naohiro Aota authored
We call split_zoned_em() on an extent_map on submitting a bio for it. Thus, we can assume the extent_map is PINNED, not LOGGING, and in the modified list. Add ASSERT()s to ensure the extent_maps after the split also has the proper flags set and are in the modified list. Suggested-by:
Filipe Manana <fdmanana@suse.com> Reviewed-by:
Johannes Thumshirn <johannes.thumshirn@wdc.com> Signed-off-by:
Naohiro Aota <naohiro.aota@wdc.com> Signed-off-by:
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Naohiro Aota authored
alloc_offset is offset from the start of a block group and @offset is actually an address in logical space. Thus, we need to consider block_group->start when calculating them. Fixes: 011b41bf ("btrfs: zoned: advance allocation pointer after tree log node") CC: stable@vger.kernel.org # 5.12+ Signed-off-by:
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Naohiro Aota authored
btrfs_relocate_chunk() can fail with -EAGAIN when e.g. send operations are running. The message can fail btrfs/187 and it's unnecessary because we anyway add it back to the reclaim list. btrfs_reclaim_bgs_work() `-> btrfs_relocate_chunk() `-> btrfs_relocate_block_group() `-> reloc_chunk_start() `-> if (fs_info->send_in_progress) `-> return -EAGAIN CC: stable@vger.kernel.org # 5.13+ Fixes: 18bb8bbf ("btrfs: zoned: automatically reclaim zones") Reviewed-by: -
Johannes Thumshirn authored
Automatically reclaiming dirty zones might not always be desired for all workloads, especially as there are currently still some rough edges with the relocation code on zoned filesystems. Allow disabling zone auto reclaim on a per filesystem basis by writing 0 as the threshold value. Reviewed-by:
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Filipe Manana authored
A comment at log_conflicting_inodes() mentions that we check the inode's logged_trans field instead of using btrfs_inode_in_log() because the field last_log_commit is not updated when we log that an inode exists and the inode has the full sync flag (BTRFS_INODE_NEEDS_FULL_SYNC) set. The part about the full sync flag is not true anymore since commit 9acc8103 ("btrfs: fix unpersisted i_size on fsync after expanding truncate"), so update the comment to not mention that part anymore. Signed-off-by:
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Filipe Manana authored
Now that we are checking if the inode's logged_trans is 0 to detect the possibility of the inode having been evicted and reloaded, the test for the full sync flag (BTRFS_INODE_NEEDS_FULL_SYNC) is no longer needed at tree-log.c:inode_logged(). Its purpose was to detect the possibility of a previous eviction as well, since when an inode is loaded the full sync flag is always set on it (and only cleared after the inode is logged). So just remove the check and update the comment. The check for the inode's logged_trans being 0 was added recently by the patch with the subject "btrfs: eliminate some false positives when checking if inode was logged". Signed-off-by:
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Filipe Manana authored
At the very end of btrfs_rename_exchange(), in case an error happened, we are checking if 'new_inode' is NULL, but that is not needed since during a rename exchange, unlike regular renames, 'new_inode' can never be NULL, and if it were, we would have a crashed much earlier when we dereference it multiple times. So remove the check because it is not necessary and because it is causing static checkers to emit a warning. I probably introduced the check by copy-pasting similar code from btrfs_rename(), where 'new_inode' can be NULL, in commit 86e8aa0e ("Btrfs: unpin logs if rename exchange operation fails"). Reported-by:
kernel test robot <lkp@intel.com> Reported-by:
Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by:
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Goldwyn Rodrigues authored
Instead of using kmalloc() to allocate backref_ctx, allocate backref_ctx on stack. The size is reasonably small. sizeof(backref_ctx) = 48 Reviewed-by:
Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by:
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Goldwyn Rodrigues authored
Instead of using kmalloc() to allocate btrfs_ioctl_defrag_range_args, allocate btrfs_ioctl_defrag_range_args on stack, the size is reasonably small and ioctls are called in process context. sizeof(btrfs_ioctl_defrag_range_args) = 48 Reviewed-by:
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Goldwyn Rodrigues authored
Instead of using kmalloc() to allocate btrfs_ioctl_quota_rescan_args, allocate btrfs_ioctl_quota_rescan_args on stack, the size is reasonably small and ioctls are called in process context. sizeof(btrfs_ioctl_quota_rescan_args) = 64 Reviewed-by:
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Goldwyn Rodrigues authored
Instead of allocating file_ra_state using kmalloc, allocate on stack. sizeof(struct readahead) = 32 bytes. Reviewed-by:
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Marcos Paulo de Souza authored
It's a common practice to start a search using offset (u64)-1, which is the u64 maximum value, meaning that we want the search_slot function to be set in the last item with the same objectid and type. Once we are in this position, it's a matter to start a search backwards by calling btrfs_previous_item, which will check if we'll need to go to a previous leaf and other necessary checks, only to be sure that we are in last offset of the same object and type. The new btrfs_search_backwards function does the all these steps when necessary, and can be used to avoid code duplication. Signed-off-by:
Marcos Paulo de Souza <mpdesouza@suse.com> Reviewed-by:
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David Sterba authored
As fsverity support depends on a config option, print that at module load time like we do for similar features. Reviewed-by:
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Boris Burkov authored
Writing out the verity data is too large of an operation to do in a single transaction. If we are interrupted before we finish creating fsverity metadata for a file, or fail to clean up already created metadata after a failure, we could leak the verity items that we already committed. To address this issue, we use the orphan mechanism. When we start enabling verity on a file, we also add an orphan item for that inode. When we are finished, we delete the orphan. However, if we are interrupted midway, the orphan will be present at mount and we can cleanup the half-formed verity state. There is a possible race with a normal unlink operation: if unlink and verity run on the same file in parallel, it is possible for verity to succeed and delete the still legitimate orphan added by unlink. Then, if we are interrupted and mount in that state, we will never clean up the inode properly. This is also possible for a file created with O_TMPFILE. Check nlink==0 before deleting to avoid this race. A final thing to note is that this is a resurrection of using orphans to signal an operation besides "delete this inode". The old case was to signal the need to do a truncate. That case still technically applies for mounting very old file systems, so we need to take some care to not clobber it. To that end, we just have to be careful that verity orphan cleanup is a no-op for non-verity files. Signed-off-by:
Boris Burkov <boris@bur.io> Reviewed-by:
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Boris Burkov authored
Add support for fsverity in btrfs. To support the generic interface in fs/verity, we add two new item types in the fs tree for inodes with verity enabled. One stores the per-file verity descriptor and btrfs verity item and the other stores the Merkle tree data itself. Verity checking is done in end_page_read just before a page is marked uptodate. This naturally handles a variety of edge cases like holes, preallocated extents, and inline extents. Some care needs to be taken to not try to verity pages past the end of the file, which are accessed by the generic buffered file reading code under some circumstances like reading to the end of the last page and trying to read again. Direct IO on a verity file falls back to buffered reads. Verity relies on PageChecked for the Merkle tree data itself to avoid re-walking up shared paths in the tree. For this reason, we need to cache the Merkle tree data. Since the file is immutable after verity is turned on, we can cache it at an index past EOF. Use the new inode ro_flags to store verity on the inode item, so that we can enable verity on a file, then rollback to an older kernel and still mount the file system and read the file. Since we can't safely write the file anymore without ruining the invariants of the Merkle tree, we mark a ro_compat flag on the file system when a file has verity enabled. Acked-by:
Eric Biggers <ebiggers@google.com> Co-developed-by:
Chris Mason <clm@fb.com> Signed-off-by:
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Boris Burkov authored
Currently, inode flags are fully backwards incompatible in btrfs. If we introduce a new inode flag, then tree-checker will detect it and fail. This can even cause us to fail to mount entirely. To make it possible to introduce new flags which can be read-only compatible, like VERITY, we add new ro flags to btrfs without treating them quite so harshly in tree-checker. A read-only file system can survive an unexpected flag, and can be mounted. As for the implementation, it unfortunately gets a little complicated. The on-disk representation of the inode, btrfs_inode_item, has an __le64 for flags but the in-memory representation, btrfs_inode, uses a u32. David Sterba had the nice idea that we could reclaim those wasted 32 bits on disk and use them for the new ro_compat flags. It turns out that the tree-checker code which checks for unknown flags is broken, and ignores the upper 32 bits we are hoping to use. The issue is that the flags use the literal 1 rather than 1ULL, so the flags are signed ints, and one of them is specifically (1 << 31). As a result, the mask which ORs the flags is a negative integer on machines where int is 32 bit twos complement. When tree-checker evaluates the expression: btrfs_inode_flags(leaf, iitem) & ~BTRFS_INODE_FLAG_MASK) The mask is something like 0x80000abc, which gets promoted to u64 with sign extension to 0xffffffff80000abc. Negating that 64 bit mask leaves all the upper bits zeroed, and we can't detect unexpected flags. This suggests that we can't use those bits after all. Luckily, we have good reason to believe that they are zero anyway. Inode flags are metadata, which is always checksummed, so any bit flips that would introduce 1s would cause a checksum failure anyway (excluding the improbable case of the checksum getting corrupted exactly badly). Further, unless the 1 << 31 flag is used, the cast to u64 of the 32 bit inode flag should preserve its value and not add leading zeroes (at least for twos complement). The only place that flag (BTRFS_INODE_ROOT_ITEM_INIT) is used is in a special inode embedded in the root item, and indeed for that inode we see 0xffffffff80000000 as the flags on disk. However, that inode is never seen by tree checker, nor is it used in a context where verity might be meaningful. Theoretically, a future ro flag might cause trouble on that inode, so we should proactively clean up that mess before it does. With the introduction of the new ro flags, keep two separate unsigned masks and check them against the appropriate u32. Since we no longer run afoul of sign extension, this also stops writing out 0xffffffff80000000 in root_item inodes going forward. Signed-off-by:
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Anand Jain authored
Function btrfs_check_raid_min_devices() returns error code from the enum btrfs_err_code and it starts from 1. So there is no need to check if ret is > 0. So drop this check and also drop the local variable ret. Signed-off-by:
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Qu Wenruo authored
When btrfs_run_delalloc_range() failed, we will error out. But there is a strange comment mentioning that btrfs_run_delalloc_range() could have returned value >0 to indicate the IO has already started. Commit 40f76580 ("Btrfs: split up __extent_writepage to lower stack usage") introduced the comment, but unfortunately at that time, we were already using @page_started to indicate that case, and still return 0. Furthermore, even if that comment was right (which is not), we would return -EIO if the IO had already started. By all means the comment is incorrect, just remove the comment along with the dead check. Just to be extra safe, add an ASSERT() in btrfs_run_delalloc_range() to make sure we either return 0 or error, no positive return value. Signed-off-by:
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