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Sat, 29 Mar 2025 04:17:20 -0700 (PDT) Received: from qasdev.Home ([2a02:c7c:6696:8300:c564:b82e:4883:713c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43d8ff042bcsm57170215e9.28.2025.03.29.04.17.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 29 Mar 2025 04:17:20 -0700 (PDT) From: Qasim Ijaz To: mark@fasheh.com, jlbec@evilplan.org, joseph.qi@linux.alibaba.com Cc: ocfs2-devel@lists.linux.dev, linux-kernel@vger.kernel.org, syzbot , stable@vger.kernel.org Subject: [PATCH RESEND] ocfs2: Validate chain list bits per cluster to prevent div-by-zero Date: Sat, 29 Mar 2025 11:16:54 +0000 Message-Id: <20250329111654.5764-1-qasdev00@gmail.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: ocfs2-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 The call trace shows that the div error occurs on the following line where the code sets the e_cpos member of the extent record while dividing bg_bits by the bits per cluster value from the chain list: rec->e_cpos = cpu_to_le32(le16_to_cpu(bg->bg_bits) / le16_to_cpu(cl->cl_bpc)); Looking at the code disassembly we see the problem occurred during the divw instruction which performs a 16-bit unsigned divide operation. The main ways a divide error can occur is if: 1) the divisor is 0 2) if the quotient is too large for the designated register (overflow). Normally the divisor being 0 is the most common cause for a division error to occur. Focusing on the bits per cluster cl->cl_bpc (since it is the divisor) we see that cl is created in ocfs2_block_group_alloc(), cl is derived from ocfs2_dinode->id2.i_chain. To fix this issue we should verify the cl_bpc member in the chain list to ensure it is valid and non-zero. Looking through the rest of the OCFS2 code it seems like there are other places which could benefit from improved checks of the cl_bpc members of chain lists like the following: In ocfs2_group_extend(): cl_bpc = le16_to_cpu(fe->id2.i_chain.cl_bpc); if (le16_to_cpu(group->bg_bits) / cl_bpc + new_clusters > le16_to_cpu(fe->id2.i_chain.cl_cpg)) { ret = -EINVAL; goto out_unlock; } Reported-by: syzbot Closes: https://syzkaller.appspot.com/bug?extid=e41e83af7a07a4df8051 Cc: stable@vger.kernel.org Signed-off-by: Qasim Ijaz --- fs/ocfs2/resize.c | 4 ++-- fs/ocfs2/suballoc.c | 5 +++++ 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/fs/ocfs2/resize.c b/fs/ocfs2/resize.c index b0733c08ed13..22352c027ecd 100644 --- a/fs/ocfs2/resize.c +++ b/fs/ocfs2/resize.c @@ -329,8 +329,8 @@ int ocfs2_group_extend(struct inode * inode, int new_clusters) group = (struct ocfs2_group_desc *)group_bh->b_data; cl_bpc = le16_to_cpu(fe->id2.i_chain.cl_bpc); - if (le16_to_cpu(group->bg_bits) / cl_bpc + new_clusters > - le16_to_cpu(fe->id2.i_chain.cl_cpg)) { + if (!cl_bpc || le16_to_cpu(group->bg_bits) / cl_bpc + new_clusters > + le16_to_cpu(fe->id2.i_chain.cl_cpg)) { ret = -EINVAL; goto out_unlock; } diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c index f7b483f0de2a..844cb36bd7ab 100644 --- a/fs/ocfs2/suballoc.c +++ b/fs/ocfs2/suballoc.c @@ -671,6 +671,11 @@ static int ocfs2_block_group_alloc(struct ocfs2_super *osb, BUG_ON(ocfs2_is_cluster_bitmap(alloc_inode)); cl = &fe->id2.i_chain; + if (!le16_to_cpu(cl->cl_bpc)) { + status = -EINVAL; + goto bail; + } + status = ocfs2_reserve_clusters_with_limit(osb, le16_to_cpu(cl->cl_cpg), max_block, flags, &ac);