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Mon, 01 Dec 2025 01:25:00 -0800 (PST) Received: from localhost.localdomain ([114.79.136.226]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29bce441e59sm118620605ad.33.2025.12.01.01.24.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Dec 2025 01:25:00 -0800 (PST) From: Prithvi Tambewagh To: mark@fasheh.com, jlbec@evilplan.org, joseph.qi@linux.alibaba.com Cc: ocfs2-devel@lists.linux.dev, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linux.dev, skhan@linuxfoundation.org, david.hunter.linux@gmail.com, khalid@kernel.org, Prithvi Tambewagh , syzbot+96d38c6e1655c1420a72@syzkaller.appspotmail.com, stable@vger.kernel.org Subject: [PATCH v2] ocfs2: fix kernel BUG in ocfs2_find_victim_chain Date: Mon, 1 Dec 2025 14:54:49 +0530 Message-Id: <20251201092450.84991-1-activprithvi@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 --- 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 -- 2.34.1