Re: net/ipv6: null-ptr-deref in ip6_route_del/lock_acquire

[Cong Wang]

On Mon, Feb 27, 2017 at 7:28 AM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> Hi,
>
> I've got the following error report while fuzzing the kernel with syzkaller.
>
> On commit e5d56efc97f8240d0b5d66c03949382b6d7e5570 (Feb 26).
>
> A reproducer and .config are attached.
>
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 0 PID: 4045 Comm: a.out Not tainted 4.10.0+ #54
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff88006b6bac00 task.stack: ffff88006a688000
> RIP: 0010:__lock_acquire+0xac4/0x3270 kernel/locking/lockdep.c:3224
> RSP: 0018:ffff88006a68f250 EFLAGS: 00010006
> RAX: dffffc0000000000 RBX: dffffc0000000000 RCX: 0000000000000000
> RDX: 0000000000000006 RSI: 0000000000000000 RDI: 1ffff1000d4d1ea4
> RBP: ffff88006a68f788 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000030 R11: 0000000000000000 R12: ffff88006b6bac00
> R13: 0000000000000000 R14: ffffffff86e64ec0 R15: 0000000000000001
> FS:  00007fda492ff700(0000) GS:ffff88006ca00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000208c4000 CR3: 000000006a7e9000 CR4: 00000000000006f0
> Call Trace:
>  lock_acquire+0x241/0x580 kernel/locking/lockdep.c:3753
>  __raw_write_lock_bh ./include/linux/rwlock_api_smp.h:203
>  _raw_write_lock_bh+0x3a/0x50 kernel/locking/spinlock.c:319
>  __ip6_del_rt_siblings net/ipv6/route.c:2177
>  ip6_route_del+0x4dd/0xa70 net/ipv6/route.c:2257
>  ipv6_route_ioctl+0x62d/0x790 net/ipv6/route.c:2620
>  inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
>  sock_do_ioctl+0x65/0xb0 net/socket.c:895
>  sock_ioctl+0x28f/0x440 net/socket.c:993
>  vfs_ioctl fs/ioctl.c:43
>  do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:683
>  SYSC_ioctl fs/ioctl.c:698
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689
>  entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:204

The attached patch fixes this crash, but I am not sure if it is the
best way to fix this bug yet...

Thanks.
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f54f426..3d1b260 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2216,12 +2216,13 @@ static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 
 static int ip6_route_del(struct fib6_config *cfg)
 {
+	struct net *net = cfg->fc_nlinfo.nl_net;
 	struct fib6_table *table;
 	struct fib6_node *fn;
 	struct rt6_info *rt;
 	int err = -ESRCH;
 
-	table = fib6_get_table(cfg->fc_nlinfo.nl_net, cfg->fc_table);
+	table = fib6_get_table(net, cfg->fc_table);
 	if (!table)
 		return err;
 
@@ -2247,6 +2248,8 @@ static int ip6_route_del(struct fib6_config *cfg)
 				continue;
 			if (cfg->fc_protocol && cfg->fc_protocol != rt->rt6i_protocol)
 				continue;
+			if (rt == net->ipv6.ip6_null_entry)
+				continue;
 			dst_hold(&rt->dst);
 			read_unlock_bh(&table->tb6_lock);