From: Prithvi Tambewagh <activprithvi@gmail.com> mainline inclusion from mainline-v6.19-rc1 commit 039bef30e320827bac8990c9f29d2a68cd8adb5f category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/13326 CVE: CVE-2025-68771 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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 <activprithvi@gmail.com> 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 <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> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com> --- fs/ocfs2/suballoc.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c index 4f48003e4327..984bf3d24c23 100644 --- a/fs/ocfs2/suballoc.c +++ b/fs/ocfs2/suballoc.c @@ -1925,6 +1925,16 @@ 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; -- 2.52.0