skmsg: pass gfp argument to alloc_sk_msg()

syzbot found that alloc_sk_msg() could be called from a
non sleepable context. sk_psock_verdict_recv() uses
rcu_read_lock() protection.

We need the callers to pass a gfp_t argument to avoid issues.

syzbot report was:

BUG: sleeping function called from invalid context at include/linux/sched/mm.h:274
in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 3613, name: syz-executor414
preempt_count: 0, expected: 0
RCU nest depth: 1, expected: 0
INFO: lockdep is turned off.
CPU: 0 PID: 3613 Comm: syz-executor414 Not tainted 6.0.0-syzkaller-09589-g55be6084 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
__might_resched+0x538/0x6a0 kernel/sched/core.c:9877
might_alloc include/linux/sched/mm.h:274 [inline]
slab_pre_alloc_hook mm/slab.h:700 [inline]
slab_alloc_node mm/slub.c:3162 [inline]
slab_alloc mm/slub.c:3256 [inline]
kmem_cache_alloc_trace+0x59/0x310 mm/slub.c:3287
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:733 [inline]
alloc_sk_msg net/core/skmsg.c:507 [inline]
sk_psock_skb_ingress_self+0x5c/0x330 net/core/skmsg.c:600
sk_psock_verdict_apply+0x395/0x440 net/core/skmsg.c:1014
sk_psock_verdict_recv+0x34d/0x560 net/core/skmsg.c:1201
tcp_read_skb+0x4a1/0x790 net/ipv4/tcp.c:1770
tcp_rcv_established+0x129d/0x1a10 net/ipv4/tcp_input.c:5971
tcp_v4_do_rcv+0x479/0xac0 net/ipv4/tcp_ipv4.c:1681
sk_backlog_rcv include/net/sock.h:1109 [inline]
__release_sock+0x1d8/0x4c0 net/core/sock.c:2906
release_sock+0x5d/0x1c0 net/core/sock.c:3462
tcp_sendmsg+0x36/0x40 net/ipv4/tcp.c:1483
sock_sendmsg_nosec net/socket.c:714 [inline]
sock_sendmsg net/socket.c:734 [inline]
__sys_sendto+0x46d/0x5f0 net/socket.c:2117
__do_sys_sendto net/socket.c:2129 [inline]
__se_sys_sendto net/socket.c:2125 [inline]
__x64_sys_sendto+0xda/0xf0 net/socket.c:2125
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 43312915 ("skmsg: Get rid of unncessary memset()")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Cong Wang <cong.wang@bytedance.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skmsg.c

@@ -500,11 +500,11 @@ bool sk_msg_is_readable(struct sock *sk)
 }
 EXPORT_SYMBOL_GPL(sk_msg_is_readable);
 
-static struct sk_msg *alloc_sk_msg(void)
+static struct sk_msg *alloc_sk_msg(gfp_t gfp)
 {
 	struct sk_msg *msg;
 
-	msg = kzalloc(sizeof(*msg), __GFP_NOWARN | GFP_KERNEL);
+	msg = kzalloc(sizeof(*msg), gfp | __GFP_NOWARN);
 	if (unlikely(!msg))
 		return NULL;
 	sg_init_marker(msg->sg.data, NR_MSG_FRAG_IDS);
@@ -520,7 +520,7 @@ static struct sk_msg *sk_psock_create_ingress_msg(struct sock *sk,
 	if (!sk_rmem_schedule(sk, skb, skb->truesize))
 		return NULL;
 
-	return alloc_sk_msg();
+	return alloc_sk_msg(GFP_KERNEL);
 }
 
 static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb,
@@ -597,7 +597,7 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb,
 static int sk_psock_skb_ingress_self(struct sk_psock *psock, struct sk_buff *skb,
 				     u32 off, u32 len)
 {
-	struct sk_msg *msg = alloc_sk_msg();
+	struct sk_msg *msg = alloc_sk_msg(GFP_ATOMIC);
 	struct sock *sk = psock->sk;
 	int err;