From c94613feefd7714ad0d03a1914632c15782114ff Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Mon, 26 Aug 2019 17:06:01 -0700 Subject: [PATCH] xfs: fix maxicount division by zero error 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 Reviewed-by: Dave Chinner Reviewed-by: Carlos Maiolino --- 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 04377ab..588d446 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. -- 2.7.4