Commit c9aa81fa authored Jun 11, 2020 by Tuong Lien Committed by David S. Miller Jun 11, 2020

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 5e9eeccc ("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: c0bceb97 ("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>

parent 77f972a7

net/tipc/msg.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

net/tipc/socket.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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;

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