tipc: fix kernel WARNING in tipc_msg_append()

syzbot found the following issue:

WARNING: CPU: 0 PID: 6808 at include/linux/thread_info.h:150 check_copy_size include/linux/thread_info.h:150 [inline]
WARNING: CPU: 0 PID: 6808 at include/linux/thread_info.h:150 copy_from_iter include/linux/uio.h:144 [inline]
WARNING: CPU: 0 PID: 6808 at include/linux/thread_info.h:150 tipc_msg_append+0x49a/0x5e0 net/tipc/msg.c:242
Kernel panic - not syncing: panic_on_warn set ...

This happens after commit 5e9eeccc58f3 ("tipc: fix NULL pointer
dereference in streaming") that tried to build at least one buffer even
when the message data length is zero... However, it now exposes another
bug that the 'mss' can be zero and the 'cpy' will be negative, thus the
above kernel WARNING will appear!
The zero value of 'mss' is never expected because it means Nagle is not
enabled for the socket (actually the socket type was 'SOCK_SEQPACKET'),
so the function 'tipc_msg_append()' must not be called at all. But that
was in this particular case since the message data length was zero, and
the 'send <= maxnagle' check became true.

We resolve the issue by explicitly checking if Nagle is enabled for the
socket, i.e. 'maxnagle != 0' before calling the 'tipc_msg_append()'. We
also reinforce the function to against such a negative values if any.

Reported-by: syzbot+75139a7d2605236b0b7f@syzkaller.appspotmail.com
Fixes: c0bceb97db9e ("tipc: add smart nagle feature")
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Tuong Lien <tuong.t.lien@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index 046e4cb3aceacd4532eb02018e13cb40db099bd2..01b64869a1739396b019f83beb3a848fd494841c 100644 (file)
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -238,14 +238,14 @@ int tipc_msg_append(struct tipc_msg *_hdr, struct msghdr *m, int dlen,
                hdr = buf_msg(skb);
                curr = msg_blocks(hdr);
                mlen = msg_size(hdr);
-               cpy = min_t(int, rem, mss - mlen);
+               cpy = min_t(size_t, rem, mss - mlen);
                if (cpy != copy_from_iter(skb->data + mlen, cpy, &m->msg_iter))
                        return -EFAULT;
                msg_set_size(hdr, mlen + cpy);
                skb_put(skb, cpy);
                rem -= cpy;
                total += msg_blocks(hdr) - curr;
-       } while (rem);
+       } while (rem > 0);
        return total - accounted;
 }
 

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index 26123f4177fd2e281f5b47a59e053d9d7cb1af61..a94f38333698a8bac2dd5dc8bb63bbbafddda4a5 100644 (file)
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -1574,7 +1574,8 @@ static int __tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dlen)
                        break;
                send = min_t(size_t, dlen - sent, TIPC_MAX_USER_MSG_SIZE);
                blocks = tsk->snd_backlog;
-               if (tsk->oneway++ >= tsk->nagle_start && send <= maxnagle) {
+               if (tsk->oneway++ >= tsk->nagle_start && maxnagle &&
+                   send <= maxnagle) {
                        rc = tipc_msg_append(hdr, m, send, maxnagle, txq);
                        if (unlikely(rc < 0))
                                break;