f2fs: fix to avoid accessing xattr across the boundary

When we traverse xattr entries via __find_xattr(),
if the raw filesystem content is faked or any hardware failure occurs,
out-of-bound error can be detected by KASAN.
Fix the issue by introducing boundary check.

[   38.402878] c7   1827 BUG: KASAN: slab-out-of-bounds in f2fs_getxattr+0x518/0x68c
[   38.402891] c7   1827 Read of size 4 at addr ffffffc0b6fb35dc by task
[   38.402935] c7   1827 Call trace:
[   38.402952] c7   1827 [<ffffff900809003c>] dump_backtrace+0x0/0x6bc
[   38.402966] c7   1827 [<ffffff9008090030>] show_stack+0x20/0x2c
[   38.402981] c7   1827 [<ffffff900871ab10>] dump_stack+0xfc/0x140
[   38.402995] c7   1827 [<ffffff9008325c40>] print_address_description+0x80/0x2d8
[   38.403009] c7   1827 [<ffffff900832629c>] kasan_report_error+0x198/0x1fc
[   38.403022] c7   1827 [<ffffff9008326104>] kasan_report_error+0x0/0x1fc
[   38.403037] c7   1827 [<ffffff9008325000>] __asan_load4+0x1b0/0x1b8
[   38.403051] c7   1827 [<ffffff90085fcc44>] f2fs_getxattr+0x518/0x68c
[   38.403066] c7   1827 [<ffffff90085fc508>] f2fs_xattr_generic_get+0xb0/0xd0
[   38.403080] c7   1827 [<ffffff9008395708>] __vfs_getxattr+0x1f4/0x1fc
[   38.403096] c7   1827 [<ffffff9008621bd0>] inode_doinit_with_dentry+0x360/0x938
[   38.403109] c7   1827 [<ffffff900862d6cc>] selinux_d_instantiate+0x2c/0x38
[   38.403123] c7   1827 [<ffffff900861b018>] security_d_instantiate+0x68/0x98
[   38.403136] c7   1827 [<ffffff9008377db8>] d_splice_alias+0x58/0x348
[   38.403149] c7   1827 [<ffffff900858d16c>] f2fs_lookup+0x608/0x774
[   38.403163] c7   1827 [<ffffff900835eacc>] lookup_slow+0x1e0/0x2cc
[   38.403177] c7   1827 [<ffffff9008367fe0>] walk_component+0x160/0x520
[   38.403190] c7   1827 [<ffffff9008369ef4>] path_lookupat+0x110/0x2b4
[   38.403203] c7   1827 [<ffffff900835dd38>] filename_lookup+0x1d8/0x3a8
[   38.403216] c7   1827 [<ffffff900835eeb0>] user_path_at_empty+0x54/0x68
[   38.403229] c7   1827 [<ffffff9008395f44>] SyS_getxattr+0xb4/0x18c
[   38.403241] c7   1827 [<ffffff9008084200>] el0_svc_naked+0x34/0x38
Signed-off-by: Randall Huang <huangrandall@google.com>
[Jaegeuk Kim: Fix wrong ending boundary]
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

CVE-2019-9453
[back-ported from commit 2777e654]
[ben_r: adjusted patch, add def for VALID_XATTR_BLOCK_SIZE ]
Signed-off-by: Benjamin M Romer <benjamin.romer@canonical.com>
Acked-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

fs/f2fs/xattr.c

@@ -248,12 +248,17 @@ static inline const struct xattr_handler *f2fs_xattr_handler(int index)
 	return handler;
 }
 
-static struct f2fs_xattr_entry *__find_xattr(void *base_addr, int index,
+static struct f2fs_xattr_entry *__find_xattr(void *base_addr,
+				void *last_base_addr, int index,
 				size_t len, const char *name)
 {
 	struct f2fs_xattr_entry *entry;
 
 	list_for_each_xattr(entry, base_addr) {
+		if ((void *)(entry) + sizeof(__u32) > last_base_addr ||
+		    (void *)XATTR_NEXT_ENTRY(entry) > last_base_addr)
+			return NULL;
+
 		if (entry->e_name_index != index)
 			continue;
 		if (entry->e_name_len != len)
@@ -401,9 +406,10 @@ int f2fs_getxattr(struct inode *inode, int index, const char *name,
 		void *buffer, size_t buffer_size, struct page *ipage)
 {
 	struct f2fs_xattr_entry *entry;
-	void *base_addr;
+	void *base_addr, *last_base_addr;
 	int error = 0;
 	size_t size, len;
+	nid_t xnid = F2FS_I(inode)->i_xattr_nid;
 
 	if (name == NULL)
 		return -EINVAL;
@@ -416,7 +422,9 @@ int f2fs_getxattr(struct inode *inode, int index, const char *name,
 	if (!base_addr)
 		return -ENOMEM;
 
-	entry = __find_xattr(base_addr, index, len, name);
+	last_base_addr = (void *)base_addr + XATTR_SIZE(xnid, inode);
+	
+	entry = __find_xattr(base_addr, last_base_addr, index, len, name);
 	if (IS_XATTR_LAST_ENTRY(entry)) {
 		error = -ENODATA;
 		goto cleanup;
@@ -483,7 +491,9 @@ static int __f2fs_setxattr(struct inode *inode, int index,
 {
 	struct f2fs_inode_info *fi = F2FS_I(inode);
 	struct f2fs_xattr_entry *here, *last;
-	void *base_addr;
+	void *base_addr, *last_base_addr;
+	nid_t xnid = F2FS_I(inode)->i_xattr_nid;
+
 	int found, newsize;
 	size_t len;
 	__u32 new_hsize;
@@ -507,8 +517,14 @@ static int __f2fs_setxattr(struct inode *inode, int index,
 	if (!base_addr)
 		goto exit;
 
+	last_base_addr = (void *)base_addr + XATTR_SIZE(xnid, inode);
+
 	/* find entry with wanted name. */
-	here = __find_xattr(base_addr, index, len, name);
+	here = __find_xattr(base_addr, last_base_addr, index, len, name);
+	if (!here) {
+		error = -EFAULT;
+		goto exit;
+	}
 
 	found = IS_XATTR_LAST_ENTRY(here) ? 0 : 1;
 

fs/f2fs/xattr.h

@@ -72,7 +72,9 @@ struct f2fs_xattr_entry {
 		for (entry = XATTR_FIRST_ENTRY(addr);\
 				!IS_XATTR_LAST_ENTRY(entry);\
 				entry = XATTR_NEXT_ENTRY(entry))
-
+#define VALID_XATTR_BLOCK_SIZE	(PAGE_SIZE - sizeof(struct node_footer))
+#define XATTR_SIZE(x,i)		(((x) ? VALID_XATTR_BLOCK_SIZE : 0) +	\
+						(inline_xattr_size(i)))
 #define MIN_OFFSET(i)	XATTR_ALIGN(inline_xattr_size(i) + PAGE_SIZE -	\
 				sizeof(struct node_footer) - sizeof(__u32))