WARNING: kmalloc bug in xfrm_add_sa

Hello,

syzbot hit the following crash on upstream commit
581e400ff935d34d95811258586128bf11baef15 (Wed Feb 7 22:29:34 2018 +0000)
Merge tag 'modules-for-v4.16' of  
git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux

So far this crash happened 2 times on upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

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Reported-by: syzbot+0ab777c27d2bb7588f73@syzkaller.appspotmail.com
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audit: type=1400 audit(1518094627.868:7): avc:  denied  { map } for   
pid=4171 comm="syzkaller731818" path="/root/syzkaller731818472" dev="sda1"  
ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023  
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
WARNING: CPU: 1 PID: 4172 at mm/slab_common.c:1012 kmalloc_slab+0x5d/0x70  
mm/slab_common.c:1012
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 4172 Comm: syzkaller731818 Not tainted 4.15.0+ #302
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x194/0x257 lib/dump_stack.c:53
  panic+0x1e4/0x41c kernel/panic.c:183
  __warn+0x1dc/0x200 kernel/panic.c:547
  report_bug+0x211/0x2d0 lib/bug.c:184
  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
  fixup_bug arch/x86/kernel/traps.c:247 [inline]
  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
  invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:988
RIP: 0010:kmalloc_slab+0x5d/0x70 mm/slab_common.c:1012
RSP: 0018:ffff8801bb7af2f0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 00000000fffff5bc RCX: ffffffff84c14688
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000fffff5bc
RBP: ffff8801bb7af2f0 R08: 0000000000000000 R09: 1ffff100376f5e21
R10: ffff8801bb7af040 R11: 0000000000000001 R12: 00000000fffff5bc
R13: ffff8801bb7af598 R14: 00000000014080c0 R15: ffff8801c8224dc0
  __do_kmalloc mm/slab.c:3700 [inline]
  __kmalloc+0x25/0x760 mm/slab.c:3714
  kmalloc include/linux/slab.h:517 [inline]
  kzalloc include/linux/slab.h:701 [inline]
  xfrm_alloc_replay_state_esn net/xfrm/xfrm_user.c:442 [inline]
  xfrm_state_construct net/xfrm/xfrm_user.c:601 [inline]
  xfrm_add_sa+0x1b15/0x3440 net/xfrm/xfrm_user.c:647
  xfrm_user_rcv_msg+0x41c/0x860 net/xfrm/xfrm_user.c:2595
  netlink_rcv_skb+0x14b/0x380 net/netlink/af_netlink.c:2442
  xfrm_netlink_rcv+0x6f/0x90 net/xfrm/xfrm_user.c:2603
  netlink_unicast_kernel net/netlink/af_netlink.c:1308 [inline]
  netlink_unicast+0x4c4/0x6b0 net/netlink/af_netlink.c:1334
  netlink_sendmsg+0xa4a/0xe60 net/netlink/af_netlink.c:1897
  sock_sendmsg_nosec net/socket.c:630 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:640
  ___sys_sendmsg+0x767/0x8b0 net/socket.c:2046
  __sys_sendmsg+0xe5/0x210 net/socket.c:2080
  SYSC_sendmsg net/socket.c:2091 [inline]
  SyS_sendmsg+0x2d/0x50 net/socket.c:2087
  do_syscall_64+0x282/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x26/0x9b
RIP: 0033:0x445a09
RSP: 002b:00007ff29bc19da8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000006dac24 RCX: 0000000000445a09
RDX: 0000000000000000 RSI: 000000002014f000 RDI: 0000000000000003
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0073746174735f68
R13: 7361682f6376612f R14: 78756e696c65732f R15: 0000000000000004
Dumping ftrace buffer:
    (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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The sanity test added in ecd7918745234 can be bypassed, validation
only occurs if XFRM_STATE_ESN flag is set, but rest of code doesn't care
and just checks if the attribute itself is present.

So always validate.  Alternative is to reject if we have the attribute
without the flag but that would change abi.

Reported-by: syzbot+0ab777c27d2bb7588f73@syzkaller.appspotmail.com
Cc: Mathias Krause <redacted>
Fixes: ecd7918745234 ("xfrm_user: ensure user supplied esn replay window is valid")
Fixes: d8647b79c3b7e ("xfrm: Add user interface for esn and big anti-replay windows")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/xfrm/xfrm_user.c | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 7f52b8eb177d..080035f056d9 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c

@@ -121,22 +121,17 @@ static inline int verify_replay(struct xfrm_usersa_info *p,
 	struct nlattr *rt = attrs[XFRMA_REPLAY_ESN_VAL];
 	struct xfrm_replay_state_esn *rs;
 
-	if (p->flags & XFRM_STATE_ESN) {
-		if (!rt)
-			return -EINVAL;
+	if (!rt)
+		return (p->flags & XFRM_STATE_ESN) ? -EINVAL : 0;
 
-		rs = nla_data(rt);
+	rs = nla_data(rt);
 
-		if (rs->bmp_len > XFRMA_REPLAY_ESN_MAX / sizeof(rs->bmp[0]) / 8)
-			return -EINVAL;
-
-		if (nla_len(rt) < (int)xfrm_replay_state_esn_len(rs) &&
-		    nla_len(rt) != sizeof(*rs))
-			return -EINVAL;
-	}
+	if (rs->bmp_len > XFRMA_REPLAY_ESN_MAX / sizeof(rs->bmp[0]) / 8)
+		return -EINVAL;
 
-	if (!rt)
-		return 0;
+	if (nla_len(rt) < (int)xfrm_replay_state_esn_len(rs) &&
+	    nla_len(rt) != sizeof(*rs))
+		return -EINVAL;
 
 	/* As only ESP and AH support ESN feature. */
 	if ((p->id.proto != IPPROTO_ESP) && (p->id.proto != IPPROTO_AH))

-- 
2.13.6

On Mon, Feb 12, 2018 at 02:42:01PM +0100, Florian Westphal wrote:

The sanity test added in ecd7918745234 can be bypassed, validation
only occurs if XFRM_STATE_ESN flag is set, but rest of code doesn't care
and just checks if the attribute itself is present.

So always validate.  Alternative is to reject if we have the attribute
without the flag but that would change abi.

Reported-by: syzbot+0ab777c27d2bb7588f73@syzkaller.appspotmail.com
Cc: Mathias Krause <redacted>
Fixes: ecd7918745234 ("xfrm_user: ensure user supplied esn replay window is valid")
Fixes: d8647b79c3b7e ("xfrm: Add user interface for esn and big anti-replay windows")
Signed-off-by: Florian Westphal <fw@strlen.de>

Patch applied, thanks Florian!