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xfs: fix bmv_count confusion w/ shared extents 

In a bmapx call, bmv_count is the total size of the array, including the
zeroth element that userspace uses to supply the search key.  The output
array starts at offset 1 so that we can set up the user for the next
invocation.  Since we now can split an extent into multiple bmap records
due to shared/unshared status, we have to be careful that we don't
overflow the output array.

In the original patch f86f403794 ("xfs: teach get_bmapx about shared
extents and the CoW fork") I used cur_ext (the output index) to check
for overflows, albeit with an off-by-one error.  Since nexleft no longer
describes the number of unfilled slots in the output, we can rip all
that out and use cur_ext for the overflow check directly.

Failure to do this causes heap corruption in bmapx callers such as
xfs_io and xfs_scrub.  xfs/328 can reproduce this problem.

Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Darrick J. Wong 2017-01-26 09:50:30 -08:00
parent 2aa6ba7b5a
commit c364b6d0b6
1 changed files with 18 additions and 10 deletions
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28
fs/xfs/xfs_bmap_util.c
View File

@ -528,7 +528,6 @@ xfs_getbmap(
xfs_bmbt_irec_t *map; /* buffer for user's data */
xfs_mount_t *mp; /* file system mount point */
int nex; /* # of user extents can do */
int nexleft; /* # of user extents left */
int subnex; /* # of bmapi's can do */
int nmap; /* number of map entries */
struct getbmapx *out; /* output structure */
@ -686,10 +685,8 @@ xfs_getbmap(
goto out_free_map;
}
nexleft = nex;
do {
nmap = (nexleft > subnex) ? subnex : nexleft;
nmap = (nex> subnex) ? subnex : nex;
error = xfs_bmapi_read(ip, XFS_BB_TO_FSBT(mp, bmv->bmv_offset),
XFS_BB_TO_FSB(mp, bmv->bmv_length),
map, &nmap, bmapi_flags);
@ -697,8 +694,8 @@ xfs_getbmap(
goto out_free_map;
ASSERT(nmap <= subnex);
for (i = 0; i < nmap && nexleft && bmv->bmv_length &&
cur_ext < bmv->bmv_count; i++) {
for (i = 0; i < nmap && bmv->bmv_length &&
cur_ext < bmv->bmv_count - 1; i++) {
out[cur_ext].bmv_oflags = 0;
if (map[i].br_state == XFS_EXT_UNWRITTEN)
out[cur_ext].bmv_oflags |= BMV_OF_PREALLOC;
@ -760,16 +757,27 @@ xfs_getbmap(
continue;
}
/*
* In order to report shared extents accurately,
* we report each distinct shared/unshared part
* of a single bmbt record using multiple bmap
* extents. To make that happen, we iterate the
* same map array item multiple times, each
* time trimming out the subextent that we just
* reported.
*
* Because of this, we must check the out array
* index (cur_ext) directly against bmv_count-1
* to avoid overflows.
*/
if (inject_map.br_startblock != NULLFSBLOCK) {
map[i] = inject_map;
i--;
} else
nexleft--;
}
bmv->bmv_entries++;
cur_ext++;
}
} while (nmap && nexleft && bmv->bmv_length &&
cur_ext < bmv->bmv_count);
} while (nmap && bmv->bmv_length && cur_ext < bmv->bmv_count - 1);
out_free_map:
kmem_free(map);