[lvc-project] [RESEND PATCH v2] ocfs2: introduce chain list sanity check with ocfs2_check_chain_list()

[Dmitry Antipov]

Introduce 'ocfs2_check_chain_list()' to check whether a) the maximum
amount of chain records in 'struct ocfs2_chain_list' matches the value
calculated based on the filesystem block size, and b) the next free slot
index is within the valid range, and use the aforementioned function
in 'ocfs2_block_group_alloc()' and 'ocfs2_claim_suballoc_bits()'.

Reported-by: syzbot+77026564530dbc29b854 at syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=77026564530dbc29b854
Reported-by: syzbot+5054473a31f78f735416 at syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5054473a31f78f735416
Signed-off-by: Dmitry Antipov <dmantipov at yandex.ru>
---
note: resend to ensure that it's reviewed and hopefully good enough for
      mm-nonmm-unstable of -mm
v2: bail on cl->cl_next_free_rec > cl->cl_count (the name is misleading,
    cl_next_free_rec is a member count (and so can be equal to array
    size) rather than member index)
---
 fs/ocfs2/suballoc.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index 6ac4dcd54588..9969a041ab18 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -649,6 +649,16 @@ ocfs2_block_group_alloc_discontig(handle_t *handle,
 	return status ? ERR_PTR(status) : bg_bh;
 }
 
+static int ocfs2_check_chain_list(struct ocfs2_chain_list *cl,
+				  struct super_block *sb)
+{
+	if (le16_to_cpu(cl->cl_count) != ocfs2_chain_recs_per_inode(sb))
+		return -EINVAL;
+	if (le16_to_cpu(cl->cl_next_free_rec) > le16_to_cpu(cl->cl_count))
+		return -EINVAL;
+	return 0;
+}
+
 /*
  * We expect the block group allocator to already be locked.
  */
@@ -671,6 +681,10 @@ static int ocfs2_block_group_alloc(struct ocfs2_super *osb,
 	BUG_ON(ocfs2_is_cluster_bitmap(alloc_inode));
 
 	cl = &fe->id2.i_chain;
+	status = ocfs2_check_chain_list(cl, alloc_inode->i_sb);
+	if (status)
+		goto bail;
+
 	status = ocfs2_reserve_clusters_with_limit(osb,
 						   le16_to_cpu(cl->cl_cpg),
 						   max_block, flags, &ac);
@@ -1992,6 +2006,9 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
 	}
 
 	cl = (struct ocfs2_chain_list *) &fe->id2.i_chain;
+	status = ocfs2_check_chain_list(cl, ac->ac_inode->i_sb);
+	if (status)
+		goto bail;
 
 	victim = ocfs2_find_victim_chain(cl);
 	ac->ac_chain = victim;
-- 
2.51.0