ocfs2: fix out-of-bounds write in ocfs2_remove_refcount_extent

[BUG]
Unlinking a refcounted file whose refcount tree has leaf blocks
triggers a fortify panic due to an out-of-bounds write.

[CAUSE]
When the last leaf block is removed from a refcount tree,
ocfs2_remove_refcount_extent() converts the root back to leaf mode
with a bulk memset on &rb->rf_records. rf_records sits in an anonymous
union with rf_list. rf_list.l_tree_depth aliases rf_records.rl_count,
and is 0 for a single-level tree. With rl_count equal to 0, the memset
writes past the 16-byte declared size of rf_records, which the fortify
checker catches.

[FIX]
Replace the bulk memset on &rb->rf_records with a correctly-bounded
memset on rl_recs[] alone, after setting rl_count to the correct value.

Link: https://lore.kernel.org/ah3TESOsEO9j_JLU@dev
Fixes: 2f26f58df041 ("ocfs2: annotate flexible array members with __counted_by_le()")
Signed-off-by: Ian Bridges <icb@fastmail.org>
Reported-by: syzbot+3ef989aae096b30f1663@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3ef989aae096b30f1663
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
index 8eee5be4d1ed4c030c357120cd93c122053ca0df..7323bde70caaf496f3a5ab7423d506f246893339 100644 (file)
--- a/fs/ocfs2/refcounttree.c
+++ b/fs/ocfs2/refcounttree.c
@@ -2131,10 +2131,15 @@ static int ocfs2_remove_refcount_extent(handle_t *handle,
                rb->rf_flags = 0;
                rb->rf_parent = 0;
                rb->rf_cpos = 0;
-               memset(&rb->rf_records, 0, sb->s_blocksize -
-                      offsetof(struct ocfs2_refcount_block, rf_records));
+               rb->rf_records.rl_used = 0;
+               rb->rf_records.rl_reserved2 = 0;
+               rb->rf_records.rl_reserved1 = 0;
+               /* rl_count determines the memset size and fortify object size. */
                rb->rf_records.rl_count =
                                cpu_to_le16(ocfs2_refcount_recs_per_rb(sb));
+               memset(rb->rf_records.rl_recs, 0,
+                      le16_to_cpu(rb->rf_records.rl_count) *
+                      sizeof(*rb->rf_records.rl_recs));
        }
 
        ocfs2_journal_dirty(handle, ref_root_bh);