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Fri, 23 Oct 2026 04:53:03 -0700 (PDT) Received: from SurHub.localdomain ([102.208.97.12]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e38048ad9sm4787574f8f.35.2026.10.23.04.53.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Oct 2026 04:53:02 -0700 (PDT) From: Abdifatah Suruur To: linux-cifs@vger.kernel.org Cc: Paulo Alcantara , Namjae Jeon , Ronnie Sahlberg , Shyam Prasad N , Tom Talpey , Bharath SM , samba-technical@lists.samba.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] smb: client: fix fiemap wild read on empty truncated response Date: Fri, 23 Oct 2026 14:52:46 +0300 Message-ID: <20261023115246.23030-1-suruurism@gmail.com> X-Mailer: git-send-email 2.53.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit smb3_fiemap() treats -E2BIG from SMB2_ioctl() as a truncated range blob and loops for the next chunk. If the server reports STATUS_BUFFER_OVERFLOW with OutputCount == 0, SMB2_ioctl() returns -E2BIG with out_data == NULL and out_data_len == 0, and the existing length checks accept the empty result. The loop then evaluates next = out_data[num - 1].file_offset + ... with num == 0, reading 16 bytes before NULL. Reject a truncated range blob that contains no range, so the resume offset is never computed from an empty response. Also require the last range in a truncated blob to advance the resume offset without overflowing, and to stay within the requested range; a malicious or broken server could otherwise make no progress or underflow len and loop forever. Free the previous response buffer before retrying. Reproduced on 6.6.87.2 with a malicious SMB2 server that answers FSCTL_QUERY_ALLOCATED_RANGES with STATUS_BUFFER_OVERFLOW and OutputCount == 0; an FS_IOC_FIEMAP ioctl on the mount oopses in cifs_fiemap() with CR2 = fffffffffffffff8. The code path is unchanged on mainline. Cc: stable@vger.kernel.org Signed-off-by: Abdifatah Suruur --- v2: - Validate the resume offset in a truncated range blob (overflow, forward progress and remaining length) and free the previous response buffer before retrying, addressing the sashiko review of v1. fs/smb/client/smb2ops.c | 36 +++++++++++++++++++++++++++++++++--- 1 file changed, 33 insertions(+), 3 deletions(-) diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c index 20624f5dff9b..56b3b183db4b 100644 --- a/fs/smb/client/smb2ops.c +++ b/fs/smb/client/smb2ops.c @@ -4360,6 +4360,15 @@ static int smb3_fiemap(struct cifs_tcon *tcon, goto out; } + /* + * A truncated range blob must contain at least one range, otherwise + * there is no offset to resume from and out_data is NULL. + */ + if (!last_blob && out_data_len == 0) { + rc = -EINVAL; + goto out; + } + num = out_data_len / sizeof(struct file_allocated_range_buffer); for (i = 0; i < num; i++) { flags = 0; @@ -4380,10 +4389,31 @@ static int smb3_fiemap(struct cifs_tcon *tcon, } if (!last_blob) { - next = le64_to_cpu(out_data[num - 1].file_offset) + - le64_to_cpu(out_data[num - 1].length); - len = len - (next - start); + u64 last_start, last_len; + + last_start = le64_to_cpu(out_data[num - 1].file_offset); + last_len = le64_to_cpu(out_data[num - 1].length); + + /* + * A truncated range blob must advance the resume offset and + * stay within the requested range. A malicious or broken + * server could otherwise overflow the offset, make no + * progress, or underflow len and keep us looping forever. + */ + if (check_add_overflow(last_start, last_len, &next) || + next <= start) { + rc = -EINVAL; + goto out; + } + if (next - start >= len) { + rc = 0; + goto out; + } + + len -= next - start; start = next; + kfree(out_data); + out_data = NULL; goto again; } -- 2.53.0