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([183.101.168.247]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7992dc86a93sm15012439b3a.75.2025.10.14.06.02.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Oct 2025 06:02:15 -0700 (PDT) From: Jaehun Gou To: Namjae Jeon Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jaehun Gou , Seunghun Han , Jihoon Kwon Subject: [PATCH] fs: exfat: fix improper check of dentry.stream.valid_size Date: Tue, 14 Oct 2025 22:01:46 +0900 Message-ID: <20251014130146.3948175-1-p22gone@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit We found an infinite loop bug in the exFAT file system that can lead to a Denial-of-Service (DoS) condition. When a dentry in an exFAT filesystem is malformed, the following system calls — SYS_openat, SYS_ftruncate, and SYS_pwrite64 — can cause the kernel to hang. Root cause analysis shows that the size validation code in exfat_find() does not check whether dentry.stream.valid_size is negative. As a result, the system calls mentioned above can succeed and eventually trigger the DoS issue. This patch adds a check for negative dentry.stream.valid_size to prevent this vulnerability. Co-developed-by: Seunghun Han Signed-off-by: Seunghun Han Co-developed-by: Jihoon Kwon Signed-off-by: Jihoon Kwon Signed-off-by: Jaehun Gou --- fs/exfat/namei.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c index 7eb9c67fd35f..2364b49f050a 100644 --- a/fs/exfat/namei.c +++ b/fs/exfat/namei.c @@ -642,10 +642,14 @@ static int exfat_find(struct inode *dir, const struct qstr *qname, info->type = exfat_get_entry_type(ep); info->attr = le16_to_cpu(ep->dentry.file.attr); - info->size = le64_to_cpu(ep2->dentry.stream.valid_size); info->valid_size = le64_to_cpu(ep2->dentry.stream.valid_size); info->size = le64_to_cpu(ep2->dentry.stream.size); + if (info->valid_size < 0) { + exfat_fs_error(sb, "data valid size is invalid(%lld)", info->valid_size); + return -EIO; + } + if (unlikely(EXFAT_B_TO_CLU_ROUND_UP(info->size, sbi) > sbi->used_clusters)) { exfat_fs_error(sb, "data size is invalid(%lld)", info->size); return -EIO; -- 2.43.0