cifs: sanity check length of data to send before sending

We had a bug discovered recently where an upper layer function
(cifs_iovec_write) could pass down a smb_rqst with an invalid amount of
data in it. The length of the SMB frame would be correct, but the rqst
struct would cause smb_send_rqst to send nearly 4GB of data.

This should never be the case. Add some sanity checking to the beginning
of smb_send_rqst that ensures that the amount of data we're going to
send agrees with the length in the RFC1002 header. If it doesn't, WARN()
and return -EIO to the upper layers.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index b37570952846..18cd5650a5fc 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -270,6 +270,26 @@ cifs_rqst_page_to_kvec(struct smb_rqst *rqst, unsigned int idx,
                 iov->iov_len = rqst->rq_pagesz;
 }
 
+static unsigned long
+rqst_len(struct smb_rqst *rqst)
+{
+        unsigned int i;
+        struct kvec *iov = rqst->rq_iov;
+        unsigned long buflen = 0;
+
+        /* total up iov array first */
+        for (i = 0; i < rqst->rq_nvec; i++)
+                buflen += iov[i].iov_len;
+
+        /* add in the page array if there is one */
+        if (rqst->rq_npages) {
+                buflen += rqst->rq_pagesz * (rqst->rq_npages - 1);
+                buflen += rqst->rq_tailsz;
+        }
+
+        return buflen;
+}
+
 static int
 smb_send_rqst(struct TCP_Server_Info *server, struct smb_rqst *rqst)
 {
@@ -277,6 +297,7 @@ smb_send_rqst(struct TCP_Server_Info *server, struct smb_rqst *rqst)
         struct kvec *iov = rqst->rq_iov;
         int n_vec = rqst->rq_nvec;
         unsigned int smb_buf_length = get_rfc1002_length(iov[0].iov_base);
+        unsigned long send_length;
         unsigned int i;
         size_t total_len = 0, sent;
         struct socket *ssocket = server->ssocket;
@@ -285,6 +306,14 @@ smb_send_rqst(struct TCP_Server_Info *server, struct smb_rqst *rqst)
         if (ssocket == NULL)
                 return -ENOTSOCK;
 
+        /* sanity check send length */
+        send_length = rqst_len(rqst);
+        if (send_length != smb_buf_length + 4) {
+                WARN(1, "Send length mismatch(send_length=%lu smb_buf_length=%u)\n",
+                        send_length, smb_buf_length);
+                return -EIO;
+        }
+
         cifs_dbg(FYI, "Sending smb: smb_len=%u\n", smb_buf_length);
         dump_smb(iov[0].iov_base, iov[0].iov_len);