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[PATCH v3] xfs: fix possible overflow in xfs_ioc_trim()

To: xfs@xxxxxxxxxxx
Subject: [PATCH v3] xfs: fix possible overflow in xfs_ioc_trim()
From: Lukas Czerner <lczerner@xxxxxxxxxx>
Date: Wed, 21 Sep 2011 11:42:30 +0200
Cc: hch@xxxxxxxxxxxxx, Lukas Czerner <lczerner@xxxxxxxxxx>
In xfs_ioc_trim it is possible that computing the last allocation group
to discard might overflow for big start & len values, because the result
might be bigger then xfs_agnumber_t which is 32 bit long. Fix this by not
allowing the start and end block of the range to be beyond the end of the
file system.

Note that if the start is beyond the end of the file system we have to
return -EINVAL, but in the "end" case we have to truncate it to the fs
size.

Also introduce "end" variable, rather than using start+len which which
might be more confusing to get right as this bug shows.

Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
---
v2: Use sb_dblocks instead of XFS_MAX_DBLOCKS to get max block count
v3: Rework the patch

 fs/xfs/xfs_discard.c |   20 ++++++++++----------
 1 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/xfs/xfs_discard.c b/fs/xfs/xfs_discard.c
index 244e797..8a24f0c 100644
--- a/fs/xfs/xfs_discard.c
+++ b/fs/xfs/xfs_discard.c
@@ -38,7 +38,7 @@ xfs_trim_extents(
        struct xfs_mount        *mp,
        xfs_agnumber_t          agno,
        xfs_fsblock_t           start,
-       xfs_fsblock_t           len,
+       xfs_fsblock_t           end,
        xfs_fsblock_t           minlen,
        __uint64_t              *blocks_trimmed)
 {
@@ -100,7 +100,7 @@ xfs_trim_extents(
                 * down partially overlapping ranges for now.
                 */
                if (XFS_AGB_TO_FSB(mp, agno, fbno) + flen < start ||
-                   XFS_AGB_TO_FSB(mp, agno, fbno) >= start + len) {
+                   XFS_AGB_TO_FSB(mp, agno, fbno) > end) {
                        trace_xfs_discard_exclude(mp, agno, fbno, flen);
                        goto next_extent;
                }
@@ -145,7 +145,7 @@ xfs_ioc_trim(
        struct request_queue    *q = mp->m_ddev_targp->bt_bdev->bd_disk->queue;
        unsigned int            granularity = q->limits.discard_granularity;
        struct fstrim_range     range;
-       xfs_fsblock_t           start, len, minlen;
+       xfs_fsblock_t           start, end, minlen;
        xfs_agnumber_t          start_agno, end_agno, agno;
        __uint64_t              blocks_trimmed = 0;
        int                     error, last_error = 0;
@@ -165,19 +165,19 @@ xfs_ioc_trim(
         * matter as trimming blocks is an advisory interface.
         */
        start = XFS_B_TO_FSBT(mp, range.start);
-       len = XFS_B_TO_FSBT(mp, range.len);
+       end = start + XFS_B_TO_FSBT(mp, range.len) - 1;
        minlen = XFS_B_TO_FSB(mp, max_t(u64, granularity, range.minlen));
 
-       start_agno = XFS_FSB_TO_AGNO(mp, start);
-       if (start_agno >= mp->m_sb.sb_agcount)
+       if (start >= mp->m_sb.sb_dblocks)
                return -XFS_ERROR(EINVAL);
+       if (end > mp->m_sb.sb_dblocks - 1)
+               end = mp->m_sb.sb_dblocks - 1;
 
-       end_agno = XFS_FSB_TO_AGNO(mp, start + len);
-       if (end_agno >= mp->m_sb.sb_agcount)
-               end_agno = mp->m_sb.sb_agcount - 1;
+       start_agno = XFS_FSB_TO_AGNO(mp, start);
+       end_agno = XFS_FSB_TO_AGNO(mp, end);
 
        for (agno = start_agno; agno <= end_agno; agno++) {
-               error = -xfs_trim_extents(mp, agno, start, len, minlen,
+               error = -xfs_trim_extents(mp, agno, start, end, minlen,
                                          &blocks_trimmed);
                if (error)
                        last_error = error;
-- 
1.7.4.4

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