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Message-ID: <1491360338.10124.39.camel@edumazet-glaptop3.roam.corp.google.com>
Date: Tue, 04 Apr 2017 19:45:38 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: Eric Dumazet <edumazet@...gle.com>,
Andrey Konovalov <andreyknvl@...gle.com>,
"David S. Miller" <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Dmitry Vyukov <dvyukov@...gle.com>,
Kostya Serebryany <kcc@...gle.com>,
syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/ipv4: use-after-free in ipv4_mtu
On Tue, 2017-04-04 at 18:11 -0700, Cong Wang wrote:
> On Tue, Apr 4, 2017 at 11:51 AM, Eric Dumazet <edumazet@...gle.com> wrote:
> > On Tue, Apr 4, 2017 at 7:50 AM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> >>
> >> Hi,
> >>
> >> I've got the following error report while fuzzing the kernel with syzkaller.
> >>
> >> On commit a71c9a1c779f2499fb2afc0553e543f18aff6edf (4.11-rc5).
> >>
> >> Unfortunately it's not reproducible.
> >>
> >> ==================================================================
> >> BUG: KASAN: use-after-free in dst_metric_raw include/net/dst.h:176
> >> [inline] at addr ffff88003d6a965c
> >> BUG: KASAN: use-after-free in ipv4_mtu+0x3f2/0x4b0
> >> net/ipv4/route.c:1270 at addr ffff88003d6a965c
> >> Read of size 4 by task syz-executor3/20611
> >> CPU: 3 PID: 20611 Comm: syz-executor3 Not tainted 4.11.0-rc5+ #199
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> >> Call Trace:
> >> __dump_stack lib/dump_stack.c:16 [inline]
> >> dump_stack+0x292/0x398 lib/dump_stack.c:52
> >> kasan_object_err+0x1c/0x70 mm/kasan/report.c:164
> >> print_address_description mm/kasan/report.c:202 [inline]
> >> kasan_report_error mm/kasan/report.c:291 [inline]
> >> kasan_report+0x252/0x510 mm/kasan/report.c:347
> >> __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:367
> >> dst_metric_raw include/net/dst.h:176 [inline]
> >> ipv4_mtu+0x3f2/0x4b0 net/ipv4/route.c:1270
> >> dst_mtu include/net/dst.h:221 [inline]
> >> do_ip_getsockopt+0x71d/0x2290 net/ipv4/ip_sockglue.c:1433
> >> ip_getsockopt+0x90/0x230 net/ipv4/ip_sockglue.c:1578
> >> tcp_getsockopt+0x82/0xd0 net/ipv4/tcp.c:3131
> >> sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2709
> >> SYSC_getsockopt net/socket.c:1829 [inline]
> >> SyS_getsockopt+0x252/0x390 net/socket.c:1811
> >> entry_SYSCALL_64_fastpath+0x1f/0xc2
> >> RIP: 0033:0x4458d9
> >> RSP: 002b:00007fe87f452b58 EFLAGS: 00000286 ORIG_RAX: 0000000000000037
> >> RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00000000004458d9
> >> RDX: 000000000000000e RSI: 0000000000000000 RDI: 0000000000000005
> >> RBP: 00000000006e0020 R08: 0000000020db6000 R09: 0000000000000000
> >> R10: 00000000207e8000 R11: 0000000000000286 R12: 0000000000708150
> >> R13: 0000000020db8000 R14: 0000000000001000 R15: 0000000000000003
> >> Object at ffff88003d6a9658, in cache kmalloc-64 size: 64
> >> Allocated:
> >> PID = 20110
> >> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
> >> save_stack+0x43/0xd0 mm/kasan/kasan.c:513
> >> set_track mm/kasan/kasan.c:525 [inline]
> >> kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
> >> kmem_cache_alloc_trace+0x82/0x270 mm/slub.c:2745
> >> kmalloc include/linux/slab.h:490 [inline]
> >> kzalloc include/linux/slab.h:663 [inline]
> >> fib_create_info+0x8e0/0x3a30 net/ipv4/fib_semantics.c:1040
> >> fib_table_insert+0x1a5/0x1550 net/ipv4/fib_trie.c:1221
> >> ip_rt_ioctl+0xddc/0x1590 net/ipv4/fib_frontend.c:597
> >> inet_ioctl+0xf2/0x1c0 net/ipv4/af_inet.c:882
> >> sctp: [Deprecated]: syz-executor0 (pid 20638) Use of int in max_burst
> >> socket option.
> >> Use struct sctp_assoc_value instead
> >> sock_do_ioctl+0x65/0xb0 net/socket.c:906
> >> sock_ioctl+0x28f/0x440 net/socket.c:1004
> >> vfs_ioctl fs/ioctl.c:45 [inline]
> >> do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:685
> >> SYSC_ioctl fs/ioctl.c:700 [inline]
> >> SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
> >> entry_SYSCALL_64_fastpath+0x1f/0xc2
> >> Freed:
> >> PID = 4439
> >> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
> >> save_stack+0x43/0xd0 mm/kasan/kasan.c:513
> >> set_track mm/kasan/kasan.c:525 [inline]
> >> kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:589
> >> slab_free_hook mm/slub.c:1357 [inline]
> >> slab_free_freelist_hook mm/slub.c:1379 [inline]
> >> slab_free mm/slub.c:2961 [inline]
> >> kfree+0xe8/0x2b0 mm/slub.c:3882
> >> free_fib_info_rcu+0x4ba/0x5e0 net/ipv4/fib_semantics.c:218
> >> __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
> >> rcu_do_batch.isra.64+0x947/0xcc0 kernel/rcu/tree.c:2879
> >> invoke_rcu_callbacks kernel/rcu/tree.c:3142 [inline]
> >> __rcu_process_callbacks kernel/rcu/tree.c:3109 [inline]
> >> rcu_process_callbacks+0x2cc/0xb90 kernel/rcu/tree.c:3126
> >> __do_softirq+0x2fb/0xb7d kernel/softirq.c:284
> >> Memory state around the buggy address:
> >> ffff88003d6a9500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >> ffff88003d6a9580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >> >ffff88003d6a9600: fc fc fc fc fc fc fc fc fc fc fc fb fb fb fb fb
> >> ^
> >> ffff88003d6a9680: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc
> >> ffff88003d6a9700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >> ==================================================================
> >
> > Thanks for the report Andrey
> >
> > Looking at fib->fib_metrics, I fail to understand how the following can work :
> >
> > dst_init_metrics(&rt->dst, fi->fib_metrics, true);
> >
> > In the cases fi->fib_metrics is _not_ dst_default_metrics,
> > fi->fib_metrics can be freed when the fib is deleted,
> > while dst(s) have still the 'read only pointer'.
> >
> > RCU grace period before fi->fib_metrics freeing does not help.
> >
> > Without refcounts, it looks like we need to copy the fib_metrics.
>
> The dst is obtained from sk_dst_cache which is cached for a fast
> path where fib_info is obtained in fib_lookup() without refcnt:
>
> err = fib_table_lookup(tb, flp, res, flags | FIB_LOOKUP_NOREF);
>
>
> ...
> if (!(fib_flags & FIB_LOOKUP_NOREF))
> atomic_inc(&fi->fib_clntref);
>
>
> This probably starts from:
>
> commit ebc0ffae5dfb4447e0a431ffe7fe1d467c48bbb9
> Author: Eric Dumazet <eric.dumazet@...il.com>
> Date: Tue Oct 5 10:41:36 2010 +0000
>
> fib: RCU conversion of fib_lookup()
Interesting. I might had too many beers tonight, but ...
refcount was removed in 2860583fe840 many months later
-static void rt_init_metrics(struct rtable *rt, struct fib_info *fi)
-{
- if (fi->fib_metrics != (u32 *) dst_default_metrics) {
- rt->fi = fi;
- atomic_inc(&fi->fib_clntref);
- }
- dst_init_metrics(&rt->dst, fi->fib_metrics, true);
-}
-
static struct fib_nh_exception *find_exception(struct fib_nh *nh,
__be32 daddr)
{
struct fnhe_hash_bucket *hash = nh->nh_exceptions;
@@ -1261,7 +1239,7 @@ static void rt_set_nexthop(struct rtable *rt,
__be32 daddr,
rt->rt_gateway = nh->nh_gw;
if (unlikely(fnhe))
rt_bind_exception(rt, fnhe, daddr);
- rt_init_metrics(rt, fi);
+ dst_init_metrics(&rt->dst, fi->fib_metrics, true);
#ifdef CONFIG_IP_ROUTE_CLASSID
rt->dst.tclassid = nh->nh_tclassid;
#endif
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