From: Brian Foster bfoster@redhat.com

commit 6958d11f77d45db80f7e22a21a74d4d5f44dc667 upstream.

We've had rather rare reports of bmap btree block corruption where the bmap root block has a level count of zero. The root cause of the corruption is so far unknown. We do have verifier checks to detect this form of on-disk corruption, but this doesn't cover a memory corruption variant of the problem. The latter is a reasonable possibility because the root block is part of the inode fork and can reside in-core for some time before inode extents are read.

If this occurs, it leads to a system crash such as the following:

BUG: unable to handle kernel paging request at ffffffff00000221 PF error: [normal kernel read fault] ... RIP: 0010:xfs_trans_brelse+0xf/0x200 [xfs] ... Call Trace: xfs_iread_extents+0x379/0x540 [xfs] xfs_file_iomap_begin_delay+0x11a/0xb40 [xfs] ? xfs_attr_get+0xd1/0x120 [xfs] ? iomap_write_begin.constprop.40+0x2d0/0x2d0 xfs_file_iomap_begin+0x4c4/0x6d0 [xfs] ? __vfs_getxattr+0x53/0x70 ? iomap_write_begin.constprop.40+0x2d0/0x2d0 iomap_apply+0x63/0x130 ? iomap_write_begin.constprop.40+0x2d0/0x2d0 iomap_file_buffered_write+0x62/0x90 ? iomap_write_begin.constprop.40+0x2d0/0x2d0 xfs_file_buffered_aio_write+0xe4/0x3b0 [xfs] __vfs_write+0x150/0x1b0 vfs_write+0xba/0x1c0 ksys_pwrite64+0x64/0xa0 do_syscall_64+0x5a/0x1d0 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The crash occurs because xfs_iread_extents() attempts to release an uninitialized buffer pointer as the level == 0 value prevented the buffer from ever being allocated or read. Change the level > 0 assert to an explicit error check in xfs_iread_extents() to avoid crashing the kernel in the event of localized, in-core inode corruption.

Signed-off-by: Brian Foster bfoster@redhat.com Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com [mcgrof: fixes kz#204223 ] Signed-off-by: Luis Chamberlain mcgrof@kernel.org --- fs/xfs/libxfs/xfs_bmap.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c index 3a496ffe6551..ab2465bc413a 100644 --- a/fs/xfs/libxfs/xfs_bmap.c +++ b/fs/xfs/libxfs/xfs_bmap.c @@ -1178,7 +1178,10 @@ xfs_iread_extents( * Root level must use BMAP_BROOT_PTR_ADDR macro to get ptr out. */ level = be16_to_cpu(block->bb_level); - ASSERT(level > 0); + if (unlikely(level == 0)) { + XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, mp); + return -EFSCORRUPTED; + } pp = XFS_BMAP_BROOT_PTR_ADDR(mp, block, 1, ifp->if_broot_bytes); bno = be64_to_cpu(*pp);