4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> commit 3bc53be9db21040b5d2de4d455f023c8c494aa68 upstream. syzbot is reporting stalls at nfc_llcp_send_ui_frame() [1]. This is because nfc_llcp_send_ui_frame() is retrying the loop without any delay when nonblocking nfc_alloc_send_skb() returned NULL. Since there is no need to use MSG_DONTWAIT if we retry until sock_alloc_send_pskb() succeeds, let's use blocking call. Also, in case an unexpected error occurred, let's break the loop if blocking nfc_alloc_send_skb() failed. [1] https://syzkaller.appspot.com/bug?id=4a131cc571c3733e0eff6bc673f4e36ae48f19c6 Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Reported-by: syzbot <syzbot+d29d18215e477cfbfbdd@xxxxxxxxxxxxxxxxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/nfc/llcp_commands.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/net/nfc/llcp_commands.c +++ b/net/nfc/llcp_commands.c @@ -754,11 +754,14 @@ int nfc_llcp_send_ui_frame(struct nfc_ll pr_debug("Fragment %zd bytes remaining %zd", frag_len, remaining_len); - pdu = nfc_alloc_send_skb(sock->dev, &sock->sk, MSG_DONTWAIT, + pdu = nfc_alloc_send_skb(sock->dev, &sock->sk, 0, frag_len + LLCP_HEADER_SIZE, &err); if (pdu == NULL) { - pr_err("Could not allocate PDU\n"); - continue; + pr_err("Could not allocate PDU (error=%d)\n", err); + len -= remaining_len; + if (len == 0) + len = err; + break; } pdu = llcp_add_header(pdu, dsap, ssap, LLCP_PDU_UI);
