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[68.48.65.54]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8aca478a70csm77229126d6.27.2026.04.14.12.15.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Apr 2026 12:15:36 -0700 (PDT) From: Michael Bommarito To: linux-cifs@vger.kernel.org, Namjae Jeon , Steve French Cc: Sergey Senozhatsky , Tom Talpey , stable@vger.kernel.org Subject: [PATCH 1/3] ksmbd: cap response sizes in ipc_validate_msg() Date: Tue, 14 Apr 2026 15:15:31 -0400 Message-ID: <20260414191533.1467353-2-michael.bommarito@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260414191533.1467353-1-michael.bommarito@gmail.com> References: <20260414191533.1467353-1-michael.bommarito@gmail.com> Precedence: bulk X-Mailing-List: linux-cifs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ipc_validate_msg() computes the expected message size for each response type by adding (or multiplying) attacker-controlled fields from the daemon response to a fixed struct size in unsigned int arithmetic. Three cases can overflow: KSMBD_EVENT_RPC_REQUEST: msg_sz = sizeof(struct ksmbd_rpc_command) + resp->payload_sz; KSMBD_EVENT_SHARE_CONFIG_REQUEST: msg_sz = sizeof(struct ksmbd_share_config_response) + resp->payload_sz; KSMBD_EVENT_LOGIN_REQUEST_EXT: msg_sz = sizeof(struct ksmbd_login_response_ext) + resp->ngroups * sizeof(gid_t); resp->payload_sz is __u32 and resp->ngroups is __s32. Each addition can wrap in unsigned int; the multiplication by sizeof(gid_t) mixes signed and size_t, so a negative ngroups is converted to SIZE_MAX before the multiply. A wrapped value of msg_sz that happens to equal entry->msg_sz bypasses the size check on the next line, and downstream consumers (smb2pdu.c:6742 memcpy using rpc_resp->payload_sz, kmemdup in ksmbd_alloc_user using resp_ext->ngroups) then trust the unverified length. This is the response-side analogue of aab98e2dbd64 ("ksmbd: fix integer overflows on 32 bit systems"), which hardened the request side by bounding attacker-controlled lengths against the existing KSMBD_IPC_MAX_PAYLOAD / NGROUPS_MAX caps. Apply the same caps on the response side: reject resp->payload_sz > KSMBD_IPC_MAX_PAYLOAD for RPC_REQUEST and SHARE_CONFIG_REQUEST, and reject resp->ngroups outside the signed [0, NGROUPS_MAX] range for LOGIN_REQUEST_EXT. With those caps the subsequent additions and multiplication are bounded well below UINT_MAX. Fixes: 0626e6641f6b ("cifsd: add server handler for central processing and tranport layers") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Assisted-by: Codex:gpt-5-4 Signed-off-by: Michael Bommarito --- fs/smb/server/transport_ipc.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c --- a/fs/smb/server/transport_ipc.c +++ b/fs/smb/server/transport_ipc.c @@ -497,6 +497,8 @@ static int ipc_validate_msg(struct ipc_msg_table_entry *entry) { struct ksmbd_rpc_command *resp = entry->response; + if (resp->payload_sz > KSMBD_IPC_MAX_PAYLOAD) + return -EINVAL; msg_sz = sizeof(struct ksmbd_rpc_command) + resp->payload_sz; break; } @@ -513,7 +515,8 @@ static int ipc_validate_msg(struct ipc_msg_table_entry *entry) struct ksmbd_share_config_response *resp = entry->response; if (resp->payload_sz) { - if (resp->payload_sz < resp->veto_list_sz) + if (resp->payload_sz < resp->veto_list_sz || + resp->payload_sz > KSMBD_IPC_MAX_PAYLOAD) return -EINVAL; msg_sz = sizeof(struct ksmbd_share_config_response) + @@ -526,6 +529,8 @@ static int ipc_validate_msg(struct ipc_msg_table_entry *entry) struct ksmbd_login_response_ext *resp = entry->response; if (resp->ngroups) { + if (resp->ngroups < 0 || resp->ngroups > NGROUPS_MAX) + return -EINVAL; msg_sz = sizeof(struct ksmbd_login_response_ext) + resp->ngroups * sizeof(gid_t); } -- 2.53.0