nilfs_ioctl_mark_blocks_dirty() uses bd_oblocknr to detect dead blocks
by comparing it with the current block number bd_blocknr. If they differ,
the block is considered dead and skipped.

However, bd_oblocknr should never be 0 since block 0 stores the primary
superblock and is never a valid GC target block. A corrupted ioctl
request with bd_oblocknr set to 0 causes the comparison to incorrectly
match when the lookup returns -ENOENT and sets bd_blocknr to 0, bypassing
the dead block check and calling nilfs_bmap_mark() on a non-existent
block. This causes nilfs_btree_do_lookup() to return -ENOENT, triggering
the WARN_ON(ret == -ENOENT).

Fix this by rejecting ioctl requests with bd_oblocknr set to 0 at the
beginning of each iteration.

Changes in v2:
  - Instead of adding a continue statement after setting bd_blocknr to 0,
    reject the ioctl request with -EINVAL when bd_oblocknr is 0, as block
    0 stores the primary superblock and is never a valid GC target block.
    (Suggested by Ryusuke Konishi)

Fixes: 7942b919f732 ("nilfs2: ioctl operations")
Reported-by: syzbot+98a040252119df0506f8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=98a040252119df0506f8
Suggested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Deepanshu Kartikey <Kartikey406@gmail.com>
---
 fs/nilfs2/ioctl.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index e17b8da66491..d25ba27b5203 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -736,6 +736,12 @@ static int nilfs_ioctl_mark_blocks_dirty(struct the_nilfs *nilfs,
 	int ret, i;
 
 	for (i = 0; i < nmembs; i++) {
+		/* bd_oblocknr must never be 0 as block 0
+		 * stores the primary superblock and is
+		 * never a valid GC target block
+		 */
+		if (unlikely(!bdescs[i].bd_oblocknr))
+			return -EINVAL;
 		/* XXX: use macro or inline func to check liveness */
 		ret = nilfs_bmap_lookup_at_level(bmap,
 						 bdescs[i].bd_offset,
-- 
2.43.0