[PATCH 04/10] xfs: don't scan off the end of the rt volume in xfs_rtallocate_extent_block

Darrick J. Wong
2024-08-23T00:13:06Z

From: Darrick J. Wong <djwong@kernel.org>

The loop conditional here is not quite correct because an rtbitmap block
can represent rtextents beyond the end of the rt volume. There's no way
that it makes sense to scan for free space beyond EOFS, so don't do it.
This overrun has been present since v2.6.0.

Also fix the type of bestlen, which was incorrectly converted.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/xfs_rtalloc.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index 3d78dc0940190..7e45e1c74c027 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -231,22 +231,20 @@ xfs_rtallocate_extent_block(
xfs_rtxnum_t *rtx) /* out: start rtext allocated */
{
struct xfs_mount *mp = args->mp;
- xfs_rtxnum_t besti; /* best rtext found so far */
- xfs_rtxnum_t bestlen;/* best length found so far */
+ xfs_rtxnum_t besti = -1; /* best rtext found so far */
xfs_rtxnum_t end; /* last rtext in chunk */
- int error;
xfs_rtxnum_t i; /* current rtext trying */
xfs_rtxnum_t next; /* next rtext to try */
+ xfs_rtxlen_t bestlen = 0; /* best length found so far */
int stat; /* status from internal calls */
+ int error;

/*
- * Loop over all the extents starting in this bitmap block,
- * looking for one that's long enough.
+ * Loop over all the extents starting in this bitmap block up to the
+ * end of the rt volume, looking for one that's long enough.
*/
- for (i = xfs_rbmblock_to_rtx(mp, bbno), besti = -1, bestlen = 0,
- end = xfs_rbmblock_to_rtx(mp, bbno + 1) - 1;
- i <= end;
- i++) {
+ end = min(mp->m_sb.sb_rextents, xfs_rbmblock_to_rtx(mp, bbno + 1)) - 1;
+ for (i = xfs_rbmblock_to_rtx(mp, bbno); i <= end; i++) {
/* Make sure we don't scan off the end of the rt volume. */
maxlen = xfs_rtallocate_clamp_len(mp, i, maxlen, prod);