KASAN: use-after-free Write in rxrpc_put_bundle

Hillf Danton hdanton at sina.com
Fri Sep 18 05:26:25 EDT 2020 

Wed, 16 Sep 2020 01:52:15 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    ed6d9b02 ionic: fix up debugfs after queue swap
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13d4c1b5900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d29a102d22f784ea
> dashboard link: https://syzkaller.appspot.com/bug?extid=d57aaf84dd8a550e6d91
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15fe9101900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1749d92d900000
> 
> The issue was bisected to:
> 
> commit 245500d853e9f20036cec7df4f6984ece4c6bf26
> Author: David Howells <dhowells at redhat.com>
> Date:   Wed Jul 1 10:15:32 2020 +0000
> 
>     rxrpc: Rewrite the client connection manager
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=12348911900000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=11348911900000
> console output: https://syzkaller.appspot.com/x/log.txt?x=16348911900000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+d57aaf84dd8a550e6d91 at syzkaller.appspotmail.com
> Fixes: 245500d853e9 ("rxrpc: Rewrite the client connection manager")
> 
> ==================================================================
> BUG: KASAN: use-after-free in instrument_atomic_write include/linux/instrumented.h:71 [inline]
> BUG: KASAN: use-after-free in atomic_dec_return include/asm-generic/atomic-instrumented.h:340 [inline]
> BUG: KASAN: use-after-free in rxrpc_put_bundle+0x1d/0x80 net/rxrpc/conn_client.c:141
> Write of size 4 at addr ffff8880a8669220 by task ksoftirqd/0/9
> 
> CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 5.9.0-rc3-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x198/0x1fd lib/dump_stack.c:118
>  print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383
>  __kasan_report mm/kasan/report.c:513 [inline]
>  kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
>  check_memory_region_inline mm/kasan/generic.c:186 [inline]
>  check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
>  instrument_atomic_write include/linux/instrumented.h:71 [inline]
>  atomic_dec_return include/asm-generic/atomic-instrumented.h:340 [inline]
>  rxrpc_put_bundle+0x1d/0x80 net/rxrpc/conn_client.c:141
>  rxrpc_destroy_connection+0x150/0x2f0 net/rxrpc/conn_object.c:367
>  rcu_do_batch kernel/rcu/tree.c:2428 [inline]
>  rcu_core+0x5ca/0x1130 kernel/rcu/tree.c:2656
>  __do_softirq+0x1f7/0xa91 kernel/softirq.c:298
>  run_ksoftirqd kernel/softirq.c:652 [inline]
>  run_ksoftirqd+0xcf/0x170 kernel/softirq.c:644
>  smpboot_thread_fn+0x655/0x9e0 kernel/smpboot.c:165
>  kthread+0x3b5/0x4a0 kernel/kthread.c:292
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> 
> Allocated by task 6875:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_set_track mm/kasan/common.c:56 [inline]
>  __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
>  kmem_cache_alloc_trace+0x174/0x2c0 mm/slab.c:3550
>  kmalloc include/linux/slab.h:554 [inline]
>  kzalloc include/linux/slab.h:666 [inline]
>  rxrpc_alloc_bundle+0x7e/0x290 net/rxrpc/conn_client.c:121
>  rxrpc_look_up_bundle net/rxrpc/conn_client.c:275 [inline]
>  rxrpc_prep_call net/rxrpc/conn_client.c:374 [inline]
>  rxrpc_connect_call+0x85c/0x1580 net/rxrpc/conn_client.c:710
>  rxrpc_new_client_call+0x961/0x1020 net/rxrpc/call_object.c:331
>  rxrpc_new_client_call_for_sendmsg net/rxrpc/sendmsg.c:622 [inline]
>  rxrpc_do_sendmsg+0xf14/0x136d net/rxrpc/sendmsg.c:679
>  rxrpc_sendmsg+0x420/0x630 net/rxrpc/af_rxrpc.c:560
>  sock_sendmsg_nosec net/socket.c:651 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:671
>  ____sys_sendmsg+0x331/0x810 net/socket.c:2353
>  ___sys_sendmsg+0xf3/0x170 net/socket.c:2407
>  __sys_sendmmsg+0x195/0x480 net/socket.c:2497
>  __do_sys_sendmmsg net/socket.c:2526 [inline]
>  __se_sys_sendmmsg net/socket.c:2523 [inline]
>  __x64_sys_sendmmsg+0x99/0x100 net/socket.c:2523
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 2642:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_set_track+0x1c/0x30 mm/kasan/common.c:56
>  kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:355
>  __kasan_slab_free+0xd8/0x120 mm/kasan/common.c:422
>  __cache_free mm/slab.c:3418 [inline]
>  kfree+0x10e/0x2b0 mm/slab.c:3756
>  rxrpc_put_bundle net/rxrpc/conn_client.c:146 [inline]
>  rxrpc_put_bundle+0x6b/0x80 net/rxrpc/conn_client.c:138
>  rxrpc_unbundle_conn+0x1f8/0x3d0 net/rxrpc/conn_client.c:935
>  rxrpc_clean_up_local_conns+0x38d/0x587 net/rxrpc/conn_client.c:1114
>  rxrpc_local_destroyer net/rxrpc/local_object.c:399 [inline]
>  rxrpc_local_processor+0x38d/0x5e0 net/rxrpc/local_object.c:433
>  process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
>  worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
>  kthread+0x3b5/0x4a0 kernel/kthread.c:292
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> 
> The buggy address belongs to the object at ffff8880a8669200
>  which belongs to the cache kmalloc-192 of size 192
> The buggy address is located 32 bytes inside of
>  192-byte region [ffff8880a8669200, ffff8880a86692c0)
> The buggy address belongs to the page:
> page:000000007bfb6cde refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8880a8669d00 pfn:0xa8669
> flags: 0xfffe0000000200(slab)
> raw: 00fffe0000000200 ffffea0002a42f88 ffffea00027d8f08 ffff8880aa040000
> raw: ffff8880a8669d00 ffff8880a8669000 000000010000000d 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8880a8669100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880a8669180: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> >ffff8880a8669200: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                ^
>  ffff8880a8669280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff8880a8669300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================


Put bundle on error to keep its usage count balanced.

--- a/net/rxrpc/conn_client.c
+++ b/net/rxrpc/conn_client.c
@@ -724,7 +724,8 @@ granted_channel:
 	smp_rmb();
 
 out_put_bundle:
-	rxrpc_put_bundle(bundle);
+	if (ret)
+		rxrpc_put_bundle(bundle);
 out:
 	_leave(" = %d", ret);
 	return ret;

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