From 039bef30e320827bac8990c9f29d2a68cd8adb5f Mon Sep 17 00:00:00 2001 From: Prithvi Tambewagh Date: Mon, 1 Dec 2025 18:37:11 +0530 Subject: [PATCH] ocfs2: fix kernel BUG in ocfs2_find_victim_chain syzbot reported a kernel BUG in ocfs2_find_victim_chain() because the `cl_next_free_rec` field of the allocation chain list (next free slot in the chain list) is 0, triggring the BUG_ON(!cl->cl_next_free_rec) condition in ocfs2_find_victim_chain() and panicking the kernel. To fix this, an if condition is introduced in ocfs2_claim_suballoc_bits(), just before calling ocfs2_find_victim_chain(), the code block in it being executed when either of the following conditions is true: 1. `cl_next_free_rec` is equal to 0, indicating that there are no free chains in the allocation chain list 2. `cl_next_free_rec` is greater than `cl_count` (the total number of chains in the allocation chain list) Either of them being true is indicative of the fact that there are no chains left for usage. This is addressed using ocfs2_error(), which prints the error log for debugging purposes, rather than panicking the kernel. Link: https://lkml.kernel.org/r/20251201130711.143900-1-activprithvi@gmail.com Signed-off-by: Prithvi Tambewagh Reported-by: syzbot+96d38c6e1655c1420a72@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=96d38c6e1655c1420a72 Tested-by: syzbot+96d38c6e1655c1420a72@syzkaller.appspotmail.com Reviewed-by: Joseph Qi Cc: Mark Fasheh Cc: Joel Becker Cc: Junxiao Bi Cc: Changwei Ge Cc: Jun Piao Cc: Heming Zhao Cc: Signed-off-by: Andrew Morton --- fs/ocfs2/suballoc.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c index 4b9d0ecd0981..8e6e5235b30c 100644 --- a/fs/ocfs2/suballoc.c +++ b/fs/ocfs2/suballoc.c @@ -1993,6 +1993,16 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac, } cl = (struct ocfs2_chain_list *) &fe->id2.i_chain; + if (!le16_to_cpu(cl->cl_next_free_rec) || + le16_to_cpu(cl->cl_next_free_rec) > le16_to_cpu(cl->cl_count)) { + status = ocfs2_error(ac->ac_inode->i_sb, + "Chain allocator dinode %llu has invalid next " + "free chain record %u, but only %u total\n", + (unsigned long long)le64_to_cpu(fe->i_blkno), + le16_to_cpu(cl->cl_next_free_rec), + le16_to_cpu(cl->cl_count)); + goto bail; + } victim = ocfs2_find_victim_chain(cl); ac->ac_chain = victim; -- 2.47.3