[PATCH] inet: sanitize socket() protocol value

[Vegard Nossum]

If you create a raw socket with a protocol of e.g. 0x10000, then
inet_sk(sk)->inet_num will get set to 0 since it only has room for 16
bits. This causes problems further down the line as lots of code makes
assumptions about ->inet_num, for example connect()...inet_autobind()
will attempt to call sk->sk_prot->get_port() which is invalid:

  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: [<          (null)>]           (null)
  PGD 19ea0067 PUD 19d3f067 PMD 0
  Oops: 0010 [#1] SMP
  CPU: 1 PID: 849 Comm: a.out Not tainted 4.4.0-rc4+ #287
  task: ffff880019a12640 ti: ffff88000008c000 task.ti: ffff88000008c000
  RIP: 0010:[<0000000000000000>]  [<          (null)>]           (null)
  RSP: 0018:ffff88000008fe50  EFLAGS: 00010246
  RAX: ffffffff81cc61f0 RBX: ffff880019d2ca80 RCX: 0000000000000802
  RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff880019d2ca80
  RBP: ffff88000008fe60 R08: 00007f0e6b132e80 R09: ffff880019d2ca80
  R10: ffff88001a7a72e0 R11: ffff880019a12640 R12: 000000000000000b
  R13: 0000000000400644 R14: 0000000000000000 R15: 0000000000000000
  FS:  00007f0e6b355740(0000) GS:ffff88001a900000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000000 CR3: 0000000019d3d000 CR4: 00000000001406a0
  Stack:
   ffffffff815f1c69 ffff880019d2ca80 ffff88000008fe88 ffffffff815f1cde
   0000000b0000000b ffff88000008fea0 ffff880019484000 ffff88000008ff38
   ffffffff8156f310 0000000000000000 2a2a2a2a2a2a2a2a ffffffff8100002a
  Call Trace:
   [<ffffffff815f1c69>] ? inet_autobind+0x23/0x50
   [<ffffffff815f1cde>] inet_dgram_connect+0x48/0x64
   [<ffffffff8156f310>] SYSC_connect+0x84/0xae
   [<ffffffff8156f3ed>] ? sock_alloc_file+0xb3/0x108
   [<ffffffff81132021>] ? fd_install+0x20/0x22
   [<ffffffff815700d2>] ? SYSC_socket+0x62/0x90
   [<ffffffff81570318>] SyS_connect+0x9/0xb
   [<ffffffff816fb86e>] entry_SYSCALL_64_fastpath+0x12/0x71
  Code:  Bad RIP value.
  RIP  [<          (null)>]           (null)
   RSP <ffff88000008fe50>
  CR2: 0000000000000000
  ---[ end trace bd60b4fe2edc2537 ]---

Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 net/ipv4/af_inet.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git net/ipv4/af_inet.c net/ipv4/af_inet.c
index 11c4ca1..4e1583a 100644
--- net/ipv4/af_inet.c
+++ net/ipv4/af_inet.c
@@ -316,6 +316,12 @@ lookup_protocol:
 
 	WARN_ON(!answer_prot->slab);
 
+	/* Check that the protocol we were given will actually fit in
+	 * inet->inet_num. */
+	err = -EINVAL;
+	if (protocol != (typeof(inet->inet_num)) protocol)
+		goto out;
+
 	err = -ENOBUFS;
 	sk = sk_alloc(net, PF_INET, GFP_KERNEL, answer_prot, kern);
 	if (!sk)
-- 
1.9.1

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