From: Christoph Paasch cpaasch@apple.com
syzkaller is not happy since commit fdfc5c8594c2 ("tcp: remove empty skb from write queue in error cases"):
CPU: 1 PID: 13814 Comm: syz-executor.4 Not tainted 4.14.143 #5 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011 task: ffff888040105c00 task.stack: ffff8880649c0000 RIP: 0010:tcp_sendmsg_locked+0x6b4/0x4390 net/ipv4/tcp.c:1350 RSP: 0018:ffff8880649cf718 EFLAGS: 00010206 RAX: 0000000000000014 RBX: 000000000000001e RCX: ffffc90000717000 RDX: 0000000000000077 RSI: ffffffff82e760f7 RDI: 00000000000000a0 RBP: ffff8880649cfaa8 R08: 1ffff1100c939e7a R09: ffff8880401063c8 R10: 0000000000000003 R11: 0000000000000001 R12: dffffc0000000000 R13: ffff888043d74750 R14: ffff888043d74500 R15: 000000000000001e FS: 00007f0afcb6d700(0000) GS:ffff88806cf00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000001b2ca22000 CR3: 0000000040496004 CR4: 00000000003606e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: tcp_sendmsg+0x2a/0x40 net/ipv4/tcp.c:1533 inet_sendmsg+0x173/0x4e0 net/ipv4/af_inet.c:784 sock_sendmsg_nosec net/socket.c:646 [inline] sock_sendmsg+0xc3/0x100 net/socket.c:656 SYSC_sendto+0x35d/0x5e0 net/socket.c:1766 do_syscall_64+0x241/0x680 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x42/0xb7
The problem is that we are removing an skb from the write-queue that could have been referenced by the sk_send_head. Thus, we need to check for the send_head's sanity after removing it.
This patch needs to be backported only to 4.14 and older (among those that applied the backport of fdfc5c8594c2).
Fixes: fdfc5c8594c2 ("tcp: remove empty skb from write queue in error cases") Cc: Eric Dumazet edumazet@google.com Cc: Jason Baron jbaron@akamai.com Cc: Vladimir Rutsky rutsky@google.com Cc: Soheil Hassas Yeganeh soheil@google.com Cc: Neal Cardwell ncardwell@google.com Signed-off-by: Christoph Paasch cpaasch@apple.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/ipv4/tcp.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -924,8 +924,7 @@ static void tcp_remove_empty_skb(struct { if (skb && !skb->len) { tcp_unlink_write_queue(skb, sk); - if (tcp_write_queue_empty(sk)) - tcp_chrono_stop(sk, TCP_CHRONO_BUSY); + tcp_check_send_head(sk, skb); sk_wmem_free_skb(sk, skb); } }