xfs: catch bad block numbers freeing extents.

A fuzzed filesystem crashed a kernel when freeing an extent with a
block number beyond the end of the filesystem. Convert all the debug
asserts in xfs_free_extent() to active checks so that we catch bad
extents and return that the filesytsem is corrupted rather than
crashing.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>

1 files changed, 23 insertions, 7 deletions

diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
index 4bc3c649aee4..27d64d752eab 100644
--- a/fs/xfs/xfs_alloc.c
+++ b/fs/xfs/xfs_alloc.c
@@ -2395,17 +2395,33 @@ xfs_free_extent(
         memset(&args, 0, sizeof(xfs_alloc_arg_t));
         args.tp = tp;
         args.mp = tp->t_mountp;
+
+        /*
+         * validate that the block number is legal - the enables us to detect
+         * and handle a silent filesystem corruption rather than crashing.
+         */
         args.agno = XFS_FSB_TO_AGNO(args.mp, bno);
-        ASSERT(args.agno < args.mp->m_sb.sb_agcount);
+        if (args.agno >= args.mp->m_sb.sb_agcount)
+                return EFSCORRUPTED;
+
         args.agbno = XFS_FSB_TO_AGBNO(args.mp, bno);
+        if (args.agbno >= args.mp->m_sb.sb_agblocks)
+                return EFSCORRUPTED;
+
         args.pag = xfs_perag_get(args.mp, args.agno);
-        if ((error = xfs_alloc_fix_freelist(&args, XFS_ALLOC_FLAG_FREEING)))
+        ASSERT(args.pag);
+
+        error = xfs_alloc_fix_freelist(&args, XFS_ALLOC_FLAG_FREEING);
+        if (error)
                 goto error0;
-#ifdef DEBUG
-        ASSERT(args.agbp != NULL);
-        ASSERT((args.agbno + len) <=
-                be32_to_cpu(XFS_BUF_TO_AGF(args.agbp)->agf_length));
-#endif
+
+        /* validate the extent size is legal now we have the agf locked */
+        if (args.agbno + len >
+                        be32_to_cpu(XFS_BUF_TO_AGF(args.agbp)->agf_length)) {
+                error = EFSCORRUPTED;
+                goto error0;
+        }
+
         error = xfs_free_ag_extent(tp, args.agbp, args.agno, args.agbno, len, 0);
 error0:
         xfs_perag_put(args.pag);