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Subject[PATCH 4.19 89/98] xfs: dont trip over uninitialized buffer on extent read of corrupted inode
Date
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>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Sasha Levin <sashal@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 3a496ffe6551c..ab2465bc413af 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);

--
2.20.1


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