syzbot reported a kernel BUG in ocfs2_find_victim_chain() because the `cl_next_free_rec` field of the allocation chain list is 0, triggring the BUG_ON(!cl->cl_next_free_rec) condition and panicking the kernel.
To fix this, `cl_next_free_rec` is checked inside the caller of ocfs2_find_victim_chain() i.e. ocfs2_claim_suballoc_bits() and if it is equal to 0, ocfs2_error() is called, to log the corruption and force the filesystem into read-only mode, to prevent further damage.
Reported-by: syzbot+96d38c6e1655c1420a72@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=96d38c6e1655c1420a72 Tested-by: syzbot+96d38c6e1655c1420a72@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Prithvi Tambewagh activprithvi@gmail.com --- v1->v2: - Remove extra line before the if statement in patch - Add upper limit check for cl->cl_next_free_rec in the if condition
fs/ocfs2/suballoc.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c index 6ac4dcd54588..1257c39c2c11 100644 --- a/fs/ocfs2/suballoc.c +++ b/fs/ocfs2/suballoc.c @@ -1992,6 +1992,13 @@ 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 0 chains\n", + (unsigned long long)le64_to_cpu(fe->i_blkno)); + goto bail; + }
victim = ocfs2_find_victim_chain(cl); ac->ac_chain = victim;
base-commit: 939f15e640f193616691d3bcde0089760e75b0d3