mptcp: fix possible NULL dereferences

JIRA: https://issues.redhat.com/browse/RHEL-48648
Upstream Status: linux.git

commit 445c0b6
Author: Eric Dumazet <edumazet@google.com>
Date:   Mon May 6 12:30:32 2024 +0000

    mptcp: fix possible NULL dereferences

    subflow_add_reset_reason(skb, ...) can fail.

    We can not assume mptcp_get_ext(skb) always return a non NULL pointer.

    syzbot reported:

    general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN PTI
    KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
    CPU: 0 PID: 5098 Comm: syz-executor132 Not tainted 6.9.0-rc6-syzkaller-01478-gcdc74c9d06e7 #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
     RIP: 0010:subflow_v6_route_req+0x2c7/0x490 net/mptcp/subflow.c:388
    Code: 8d 7b 07 48 89 f8 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 c0 01 00 00 0f b6 43 07 48 8d 1c c3 48 83 c3 18 48 89 d8 48 c1 e8 03 <42> 0f b6 04 20 84 c0 0f 85 84 01 00 00 0f b6 5b 01 83 e3 0f 48 89
    RSP: 0018:ffffc9000362eb68 EFLAGS: 00010206
    RAX: 0000000000000003 RBX: 0000000000000018 RCX: ffff888022039e00
    RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
    RBP: ffff88807d961140 R08: ffffffff8b6cb76b R09: 1ffff1100fb2c230
    R10: dffffc0000000000 R11: ffffed100fb2c231 R12: dffffc0000000000
    R13: ffff888022bfe273 R14: ffff88802cf9cc80 R15: ffff88802ad5a700
    FS:  0000555587ad2380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007f420c3f9720 CR3: 0000000022bfc000 CR4: 00000000003506f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     <TASK>
      tcp_conn_request+0xf07/0x32c0 net/ipv4/tcp_input.c:7180
      tcp_rcv_state_process+0x183c/0x4500 net/ipv4/tcp_input.c:6663
      tcp_v6_do_rcv+0x8b2/0x1310 net/ipv6/tcp_ipv6.c:1673
      tcp_v6_rcv+0x22b4/0x30b0 net/ipv6/tcp_ipv6.c:1910
      ip6_protocol_deliver_rcu+0xc76/0x1570 net/ipv6/ip6_input.c:438
      ip6_input_finish+0x186/0x2d0 net/ipv6/ip6_input.c:483
      NF_HOOK+0x3a4/0x450 include/linux/netfilter.h:314
      NF_HOOK+0x3a4/0x450 include/linux/netfilter.h:314
      __netif_receive_skb_one_core net/core/dev.c:5625 [inline]
      __netif_receive_skb+0x1ea/0x650 net/core/dev.c:5739
      netif_receive_skb_internal net/core/dev.c:5825 [inline]
      netif_receive_skb+0x1e8/0x890 net/core/dev.c:5885
      tun_rx_batched+0x1b7/0x8f0 drivers/net/tun.c:1549
      tun_get_user+0x2f35/0x4560 drivers/net/tun.c:2002
      tun_chr_write_iter+0x113/0x1f0 drivers/net/tun.c:2048
      call_write_iter include/linux/fs.h:2110 [inline]
      new_sync_write fs/read_write.c:497 [inline]
      vfs_write+0xa84/0xcb0 fs/read_write.c:590
      ksys_write+0x1a0/0x2c0 fs/read_write.c:643
      do_syscall_x64 arch/x86/entry/common.c:52 [inline]
      do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
     entry_SYSCALL_64_after_hwframe+0x77/0x7f

    Fixes: 3e14049 ("mptcp: support rstreason for passive reset")
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Acked-by: Paolo Abeni <pabeni@redhat.com>
    Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
    Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
    Link: https://lore.kernel.org/r/20240506123032.3351895-1-edumazet@google.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Antoine Tenart <atenart@redhat.com>

Author: atenart

net/mptcp/subflow.c

@@ -284,6 +284,16 @@ int mptcp_subflow_init_cookie_req(struct request_sock *req,
 }
 EXPORT_SYMBOL_GPL(mptcp_subflow_init_cookie_req);
 
+static enum sk_rst_reason mptcp_get_rst_reason(const struct sk_buff *skb)
+{
+	const struct mptcp_ext *mpext = mptcp_get_ext(skb);
+
+	if (!mpext)
+		return SK_RST_REASON_NOT_SPECIFIED;
+
+	return sk_rst_convert_mptcp_reason(mpext->reset_reason);
+}
+
 static struct dst_entry *subflow_v4_route_req(const struct sock *sk,
 					      struct sk_buff *skb,
 					      struct flowi *fl,
@@ -304,13 +314,9 @@ static struct dst_entry *subflow_v4_route_req(const struct sock *sk,
 		return dst;
 
 	dst_release(dst);
-	if (!req->syncookie) {
-		struct mptcp_ext *mpext = mptcp_get_ext(skb);
-		enum sk_rst_reason reason;
-
-		reason = sk_rst_convert_mptcp_reason(mpext->reset_reason);
-		tcp_request_sock_ops.send_reset(sk, skb, reason);
-	}
+	if (!req->syncookie)
+		tcp_request_sock_ops.send_reset(sk, skb,
+						mptcp_get_rst_reason(skb));
 	return NULL;
 }
 
@@ -376,13 +382,9 @@ static struct dst_entry *subflow_v6_route_req(const struct sock *sk,
 		return dst;
 
 	dst_release(dst);
-	if (!req->syncookie) {
-		struct mptcp_ext *mpext = mptcp_get_ext(skb);
-		enum sk_rst_reason reason;
-
-		reason = sk_rst_convert_mptcp_reason(mpext->reset_reason);
-		tcp6_request_sock_ops.send_reset(sk, skb, reason);
-	}
+	if (!req->syncookie)
+		tcp6_request_sock_ops.send_reset(sk, skb,
+						 mptcp_get_rst_reason(skb));
 	return NULL;
 }
 #endif
@@ -913,7 +915,7 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 	tcp_rsk(req)->drop_req = true;
 	inet_csk_prepare_for_destroy_sock(child);
 	tcp_done(child);
-	reason = sk_rst_convert_mptcp_reason(mptcp_get_ext(skb)->reset_reason);
+	reason = mptcp_get_rst_reason(skb);
 	req->rsk_ops->send_reset(sk, skb, reason);
 
 	/* The last child reference will be released by the caller */