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Date:   Tue, 4 Apr 2017 16:50:11 +0200
From:   Andrey Konovalov <>
To:     "David S. Miller" <>,
        Alexey Kuznetsov <>,
        James Morris <>,
        Hideaki YOSHIFUJI <>,
        Patrick McHardy <>,
        netdev <>,
        LKML <>
Cc:     Dmitry Vyukov <>,
        Kostya Serebryany <>,
        Eric Dumazet <>,
        syzkaller <>
Subject: net/ipv4: use-after-free in ipv4_mtu


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
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
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
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

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