From c94613feefd7714ad0d03a1914632c15782114ff Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <darrick.wong@oracle.com>
Date: Mon, 26 Aug 2019 17:06:01 -0700
Subject: [PATCH] xfs: fix maxicount division by zero error
Git-commit: c94613feefd7714ad0d03a1914632c15782114ff
Patch-mainline: v5.4-rc1
References: bsc#1166132
In xfs_ialloc_setup_geometry, it's possible for a malicious/corrupt fs
image to set an unreasonably large value for sb_inopblog which will
cause ialloc_blks to be zero. If sb_imax_pct is also set, this results
in a division by zero error in the second do_div call. Therefore, force
maxicount to zero if ialloc_blks is zero.
Note that the kernel metadata verifiers will catch the garbage inopblog
value and abort the fs mount long before it tries to set up the inode
geometry; this is needed to avoid a crash in xfs_db while setting up the
xfs_mount structure.
Found by fuzzing sb_inopblog to 122 in xfs/350.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Acked-by: Anthony Iliopoulos <ailiopoulos@suse.com>
---
fs/xfs/libxfs/xfs_ialloc.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
index 04377ab75863..588d44613094 100644
--- a/fs/xfs/libxfs/xfs_ialloc.c
+++ b/fs/xfs/libxfs/xfs_ialloc.c
@@ -2787,8 +2787,13 @@ xfs_ialloc_setup_geometry(
igeo->inobt_maxlevels = xfs_btree_compute_maxlevels(igeo->inobt_mnr,
inodes);
- /* Set the maximum inode count for this filesystem. */
- if (sbp->sb_imax_pct) {
+ /*
+ * Set the maximum inode count for this filesystem, being careful not
+ * to use obviously garbage sb_inopblog/sb_inopblock values. Regular
+ * users should never get here due to failing sb verification, but
+ * certain users (xfs_db) need to be usable even with corrupt metadata.
+ */
+ if (sbp->sb_imax_pct && igeo->ialloc_blks) {
/*
* Make sure the maximum inode count is a multiple
* of the units we allocate inodes in.
--
2.16.4