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xfs: fix memory corruption during remote attr value buffer invalidation

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While running generic/103, I observed what looks like memory corruption
and (with slub debugging turned on) a slub redzone warning on i386 when
inactivating an inode with a 64k remote attr value.

On a v5 filesystem, maximally sized remote attr values require one block
more than 64k worth of space to hold both the remote attribute value
header (64 bytes).  On a 4k block filesystem this results in a 68k
buffer; on a 64k block filesystem, this would be a 128k buffer.  Note
that even though we'll never use more than 65,600 bytes of this buffer,
XFS_MAX_BLOCKSIZE is 64k.

This is a problem because the definition of struct xfs_buf_log_format
allows for XFS_MAX_BLOCKSIZE worth of dirty bitmap (64k).  On i386 when we
invalidate a remote attribute, xfs_trans_binval zeroes all 68k worth of
the dirty map, writing right off the end of the log item and corrupting
memory.  We've gotten away with this on x86_64 for years because the
compiler inserts a u32 padding on the end of struct xfs_buf_log_format.

Fortunately for us, remote attribute values are written to disk with
xfs_bwrite(), which is to say that they are not logged.  Fix the problem
by removing all places where we could end up creating a buffer log item
for a remote attribute value and leave a note explaining why.  Next,
replace the open-coded buffer invalidation with a call to the helper we
created in the previous patch that does better checking for bad metadata
before marking the buffer stale.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Darrick J. Wong
2020-01-07 16:11:45 -08:00
parent 8edbb26b06
commit e8db2aafce
2 changed files with 46 additions and 41 deletions
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37
fs/xfs/libxfs/xfs_attr_remote.c
View File

@@ -25,6 +25,23 @@
#define ATTR_RMTVALUE_MAPSIZE 1 /* # of map entries at once */
/*
* Remote Attribute Values
* =======================
*
* Remote extended attribute values are conceptually simple -- they're written
* to data blocks mapped by an inode's attribute fork, and they have an upper
* size limit of 64k. Setting a value does not involve the XFS log.
*
* However, on a v5 filesystem, maximally sized remote attr values require one
* block more than 64k worth of space to hold both the remote attribute value
* header (64 bytes). On a 4k block filesystem this results in a 68k buffer;
* on a 64k block filesystem, this would be a 128k buffer. Note that the log
* format can only handle a dirty buffer of XFS_MAX_BLOCKSIZE length (64k).
* Therefore, we /must/ ensure that remote attribute value buffers never touch
* the logging system and therefore never have a log item.
*/
/*
* Each contiguous block has a header, so it is not just a simple attribute
* length to FSB conversion.
@@ -401,17 +418,25 @@ xfs_attr_rmtval_get(
(map[i].br_startblock != HOLESTARTBLOCK));
dblkno = XFS_FSB_TO_DADDR(mp, map[i].br_startblock);
dblkcnt = XFS_FSB_TO_BB(mp, map[i].br_blockcount);
error = xfs_trans_read_buf(mp, args->trans,
mp->m_ddev_targp,
dblkno, dblkcnt, 0, &bp,
&xfs_attr3_rmt_buf_ops);
if (error)
bp = xfs_buf_read(mp->m_ddev_targp, dblkno, dblkcnt, 0,
&xfs_attr3_rmt_buf_ops);
if (!bp)
return -ENOMEM;
error = bp->b_error;
if (error) {
xfs_buf_ioerror_alert(bp, __func__);
xfs_buf_relse(bp);
/* bad CRC means corrupted metadata */
if (error == -EFSBADCRC)
error = -EFSCORRUPTED;
return error;
}
error = xfs_attr_rmtval_copyout(mp, bp, args->dp->i_ino,
&offset, &valuelen,
&dst);
xfs_trans_brelse(args->trans, bp);
xfs_buf_relse(bp);
if (error)
return error;