• Matthew Wilcox (Oracle)'s avatar
    memfd: Fix locking when tagging pins · 99b45e7a
    Matthew Wilcox (Oracle) authored
    The RCU lock is insufficient to protect the radix tree iteration as
    a deletion from the tree can occur before we take the spinlock to
    tag the entry.  In 4.19, this has manifested as a bug with the following
    trace:
    
    kernel BUG at lib/radix-tree.c:1429!
    invalid opcode: 0000 [#1] SMP KASAN PTI
    CPU: 7 PID: 6935 Comm: syz-executor.2 Not tainted 4.19.36 #25
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
    RIP: 0010:radix_tree_tag_set+0x200/0x2f0 lib/radix-tree.c:1429
    Code: 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 89 44 24 10 e8 a3 29 7e fe 48 8b 44 24 10 48 0f ab 03 e9 d2 fe ff ff e8 90 29 7e fe <0f> 0b 48 c7 c7 e0 5a 87 84 e8 f0 e7 08 ff 4c 89 ef e8 4a ff ac fe
    RSP: 0018:ffff88837b13fb60 EFLAGS: 00010016
    RAX: 0000000000040000 RBX: ffff8883c5515d58 RCX: ffffffff82cb2ef0
    RDX: 0000000000000b72 RSI: ffffc90004cf2000 RDI: ffff8883c5515d98
    RBP: ffff88837b13fb98 R08: ffffed106f627f7e R09: ffffed106f627f7e
    R10: 0000000000000001 R11: ffffed106f627f7d R12: 0000000000000004
    R13: ffffea000d7fea80 R14: 1ffff1106f627f6f R15: 0000000000000002
    FS:  00007fa1b8df2700(0000) GS:ffff8883e2fc0000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007fa1b8df1db8 CR3: 000000037d4d2001 CR4: 0000000000160ee0
    Call Trace:
     memfd_tag_pins mm/memfd.c:51 [inline]
     memfd_wait_for_pins+0x2c5/0x12d0 mm/memfd.c:81
     memfd_add_seals mm/memfd.c:215 [inline]
     memfd_fcntl+0x33d/0x4a0 mm/memfd.c:247
     do_fcntl+0x589/0xeb0 fs/fcntl.c:421
     __do_sys_fcntl fs/fcntl.c:463 [inline]
     __se_sys_fcntl fs/fcntl.c:448 [inline]
     __x64_sys_fcntl+0x12d/0x180 fs/fcntl.c:448
     do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:293
    
    The problem does not occur in mainline due to the XArray rewrite which
    changed the locking to exclude modification of the tree during iteration.
    At the time, nobody realised this was a bugfix.  Backport the locking
    changes to stable.
    
    Cc: stable@vger.kernel.org
    Reported-by: default avatarzhong jiang <zhongjiang@huawei.com>
    Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
    Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
    99b45e7a
memfd.c 8.47 KB