sctp: fix -ENOMEM result with invalid user space pointer in sendto() syscall

Consider the following program, that sets the second argument to the
sendto() syscall incorrectly:

 #include <string.h>
 #include <arpa/inet.h>
 #include <sys/socket.h>

 int main(void)
 {
         int fd;
         struct sockaddr_in sa;

         fd = socket(AF_INET, SOCK_STREAM, 132 /*IPPROTO_SCTP*/);
         if (fd < 0)
                 return 1;

         memset(&sa, 0, sizeof(sa));
         sa.sin_family = AF_INET;
         sa.sin_addr.s_addr = inet_addr("127.0.0.1");
         sa.sin_port = htons(11111);

         sendto(fd, NULL, 1, 0, (struct sockaddr *)&sa, sizeof(sa));

         return 0;
 }

We get -ENOMEM:

 $ strace -e sendto ./demo
 sendto(3, NULL, 1, 0, {sa_family=AF_INET, sin_port=htons(11111), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 ENOMEM (Cannot allocate memory)

Propagate the error code from sctp_user_addto_chunk(), so that we will
tell user space what actually went wrong:

 $ strace -e sendto ./demo
 sendto(3, NULL, 1, 0, {sa_family=AF_INET, sin_port=htons(11111), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EFAULT (Bad address)

Noticed while running Trinity (the syscall fuzzer).

Signed-off-by: Tommi Rantala <tt.rantala@gmail.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 11 insertions, 6 deletions

diff --git a/net/sctp/chunk.c b/net/sctp/chunk.c
index f2aebdbb1eda..69ce21e3716f 100644
--- a/net/sctp/chunk.c
+++ b/net/sctp/chunk.c
@@ -183,7 +183,7 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
 
         msg = sctp_datamsg_new(GFP_KERNEL);
         if (!msg)
-                return NULL;
+                return ERR_PTR(-ENOMEM);
 
         /* Note: Calculate this outside of the loop, so that all fragments
          * have the same expiration.
@@ -280,8 +280,11 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
 
                 chunk = sctp_make_datafrag_empty(asoc, sinfo, len, frag, 0);
 
-                if (!chunk)
+                if (!chunk) {
+                        err = -ENOMEM;
                         goto errout;
+                }
+
                 err = sctp_user_addto_chunk(chunk, offset, len, msgh->msg_iov);
                 if (err < 0)
                         goto errout_chunk_free;
@@ -315,8 +318,10 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
 
                 chunk = sctp_make_datafrag_empty(asoc, sinfo, over, frag, 0);
 
-                if (!chunk)
+                if (!chunk) {
+                        err = -ENOMEM;
                         goto errout;
+                }
 
                 err = sctp_user_addto_chunk(chunk, offset, over,msgh->msg_iov);
 
@@ -342,7 +347,7 @@ errout:
                 sctp_chunk_free(chunk);
         }
         sctp_datamsg_put(msg);
-        return NULL;
+        return ERR_PTR(err);
 }
 
 /* Check whether this message has expired. */
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index a60d1f8b41c5..406d957d08fb 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1915,8 +1915,8 @@ SCTP_STATIC int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
 
         /* Break the message into multiple chunks of maximum size. */
         datamsg = sctp_datamsg_from_user(asoc, sinfo, msg, msg_len);
-        if (!datamsg) {
-                err = -ENOMEM;
+        if (IS_ERR(datamsg)) {
+                err = PTR_ERR(datamsg);
                 goto out_free;
         }