[1/6] xfs: don't trip over uninitialized buffer on extent read of corrupted inode
diff mbox series

Message ID 20190724063451.26190-2-mcgrof@kernel.org
State Accepted
Headers show
  • xfs: stable fixes for v4.19.y - circa v4.19.60
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Commit Message

Luis Chamberlain July 24, 2019, 6:34 a.m. UTC
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_write_begin.constprop.40+0x2d0/0x2d0
  ? iomap_write_begin.constprop.40+0x2d0/0x2d0
  xfs_file_buffered_aio_write+0xe4/0x3b0 [xfs]

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

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>
 fs/xfs/libxfs/xfs_bmap.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

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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)) {
+		return -EFSCORRUPTED;
+	}
 	pp = XFS_BMAP_BROOT_PTR_ADDR(mp, block, 1, ifp->if_broot_bytes);
 	bno = be64_to_cpu(*pp);