[PATCH] net: sctp: fix panic during skb_orphan()

[Vlad Yasevich <vyasevich@gmail.com>]

This patch fixes the following triggered bug ...

[  553.109742] kernel BUG at include/linux/skbuff.h:1813!
[  553.109766] invalid opcode: 0000 [#1] SMP
[  553.109789] Modules linked in: sctp libcrc32c rfcomm [...]
[  553.110259]  uinput i915 i2c_algo_bit drm_kms_helper e1000e drm ptp
pps_core i2c_core wmi video sunrpc
[  553.110320] CPU: 0 PID: 1636 Comm: lt-test_1_to_1_ Not tainted
3.11.0-rc3+ #2
[  553.110350] Hardware name: LENOVO 74597D6/74597D6, BIOS 6DET60WW
(3.10 ) 09/17/2009
[  553.110381] task: ffff88020a01dd40 ti: ffff880204ed0000 task.ti:
ffff880204ed0000
[  553.110411] RIP: 0010:[<ffffffffa0698017>]  [<ffffffffa0698017>]
skb_orphan.part.9+0x4/0x6 [sctp]
[  553.110459] RSP: 0018:ffff880204ed1bb8  EFLAGS: 00010286
[  553.110483] RAX: ffff8802086f5a40 RBX: ffff880204303300 RCX:
0000000000000000
[  553.110487] RDX: ffff880204303c28 RSI: ffff8802086f5a40 RDI:
ffff880202158000
[  553.110487] RBP: ffff880204ed1bb8 R08: 0000000000000000 R09:
0000000000000000
[  553.110487] R10: ffff88022f2d9a04 R11: ffff880233001600 R12:
0000000000000000
[  553.110487] R13: ffff880204303c00 R14: ffff8802293d0000 R15:
ffff880202158000
[  553.110487] FS:  00007f31b31fe740(0000) GS:ffff88023bc00000(0000)
knlGS:0000000000000000
[  553.110487] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  553.110487] CR2: 000000379980e3e0 CR3: 000000020d225000 CR4:
00000000000407f0
[  553.110487] Stack:
[  553.110487]  ffff880204ed1ca8 ffffffffa068d7fc 0000000000000000
0000000000000000
[  553.110487]  0000000000000000 ffff8802293d0000 ffff880202158000
ffffffff81cb7900
[  553.110487]  0000000000000000 0000400000001c68 ffff8802086f5a40
000000000000000f
[  553.110487] Call Trace:
[  553.110487]  [<ffffffffa068d7fc>] sctp_sendmsg+0x6bc/0xc80 [sctp]
[  553.110487]  [<ffffffff8128f185>] ? sock_has_perm+0x75/0x90
[  553.110487]  [<ffffffff815a3593>] inet_sendmsg+0x63/0xb0
[  553.110487]  [<ffffffff8128f2b3>] ? selinux_socket_sendmsg+0x23/0x30
[  553.110487]  [<ffffffff8151c5d6>] sock_sendmsg+0xa6/0xd0
[  553.110487]  [<ffffffff81637b05>] ? _raw_spin_unlock_bh+0x15/0x20
[  553.110487]  [<ffffffff8151cd38>] SYSC_sendto+0x128/0x180
[  553.110487]  [<ffffffff8151ce6b>] ? SYSC_connect+0xdb/0x100
[  553.110487]  [<ffffffffa0690031>] ? sctp_inet_listen+0x71/0x1f0
[sctp]
[  553.110487]  [<ffffffff8151d35e>] SyS_sendto+0xe/0x10
[  553.110487]  [<ffffffff81640202>] system_call_fastpath+0x16/0x1b
[  553.110487] Code: e0 48 c7 c7 00 22 6a a0 e8 67 a3 f0 e0 48 c7 [...]
[  553.110487] RIP  [<ffffffffa0698017>] skb_orphan.part.9+0x4/0x6
[sctp]
[  553.110487]  RSP <ffff880204ed1bb8>
[  553.121578] ---[ end trace 46c20c5903ef5be2 ]---

When a SCTP data chunk is created, skb->sk is set by sctp_make_chunk().
At a later time, sctp_sendmg() calls sctp_set_owner_w() which will attempt
to orphan the skb and correctly set the skb->sk.  The skb_orphan call result
in the above crash since skb->sk was set the the destructor was not.

The simple solution is to not set skb->sk for DATA chunks (since it
will be done later).  Continue to do it for control chunks since
sctp needs the sk at a later timer and control chunks are not currently
accouted agains socket memory.

Signed-off-by: Vlad Yasevich <vyasevich@gmail.com>
---
 net/sctp/sm_make_chunk.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 780a2d4..4ff7803 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -1385,8 +1385,12 @@ static struct sctp_chunk *sctp_make_chunk(const struct sctp_association *asoc,
 	if (sctp_auth_send_cid(type, asoc))
 		retval->auth = 1;
 
-	/* Set the skb to the belonging sock for accounting.  */
-	skb->sk = sk;
+	/* Set the skb to the belonging sock for accounting.  Do not
+	 * do this for data chunks as that will be properly set
+	 * up later.
+	 */
+	if (type != SCTP_CID_DATA)
+		skb->sk = sk;
 
 	return retval;
 nodata:
-- 
1.8.1.4