Message-ID: <159534b0fadb78c727bce6d55d358689@nuclearcat.com>
Date:   Fri, 16 Feb 2018 13:13:18 +0200
From:   Denys Fedoryshchenko <nuclearcat@...learcat.com>
To:     Guillaume Nault <g.nault@...halink.fr>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: ppp/pppoe, still panic 4.15.3 in ppp_push

On 2018-02-15 21:42, Guillaume Nault wrote:
> On Thu, Feb 15, 2018 at 09:34:42PM +0200, Denys Fedoryshchenko wrote:
>> On 2018-02-15 21:31, Guillaume Nault wrote:
>> > On Thu, Feb 15, 2018 at 06:01:16PM +0200, Denys Fedoryshchenko wrote:
>> > > On 2018-02-15 17:55, Guillaume Nault wrote:
>> > > > On Thu, Feb 15, 2018 at 12:19:52PM +0200, Denys Fedoryshchenko wrote:
>> > > > > Here we go:
>> > > > >
>> > > > >  <srv> [24558.921549]
>> > > > > ==================================================================
>> > > > >  <srv> [24558.922167] BUG: KASAN: use-after-free in
>> > > > > ppp_ioctl+0xa6a/0x1522
>> > > > > [ppp_generic]
>> > > > >  <srv> [24558.922776] Write of size 8 at addr ffff8803d35bf3f8 by task
>> > > > > accel-pppd/12622
>> > > > >  <srv> [24558.923113]
>> > > > >  <srv> [24558.923451] CPU: 0 PID: 12622 Comm: accel-pppd Tainted: G
>> > > > > W
>> > > > > 4.15.3-build-0134 #1
>> > > > >  <srv> [24558.924058] Hardware name: HP ProLiant DL320e Gen8 v2,
>> > > > > BIOS P80
>> > > > > 04/02/2015
>> > > > >  <srv> [24558.924406] Call Trace:
>> > > > >  <srv> [24558.924753]  dump_stack+0x46/0x59
>> > > > >  <srv> [24558.925103]  print_address_description+0x6b/0x23b
>> > > > >  <srv> [24558.925451]  ? ppp_ioctl+0xa6a/0x1522 [ppp_generic]
>> > > > >  <srv> [24558.925797]  kasan_report+0x21b/0x241
>> > > > >  <srv> [24558.926136]  ppp_ioctl+0xa6a/0x1522 [ppp_generic]
>> > > > >  <srv> [24558.926479]  ? ppp_nl_newlink+0x1da/0x1da [ppp_generic]
>> > > > >  <srv> [24558.926829]  ? sock_sendmsg+0x89/0x99
>> > > > >  <srv> [24558.927176]  ? __vfs_write+0xd9/0x4ad
>> > > > >  <srv> [24558.927523]  ? kernel_read+0xed/0xed
>> > > > >  <srv> [24558.927872]  ? SyS_getpeername+0x18c/0x18c
>> > > > >  <srv> [24558.928213]  ? bit_waitqueue+0x2a/0x2a
>> > > > >  <srv> [24558.928561]  ? wake_atomic_t_function+0x115/0x115
>> > > > >  <srv> [24558.928898]  vfs_ioctl+0x6e/0x81
>> > > > >  <srv> [24558.929228]  do_vfs_ioctl+0xa00/0xb10
>> > > > >  <srv> [24558.929571]  ? sigprocmask+0x1a6/0x1d0
>> > > > >  <srv> [24558.929907]  ? sigsuspend+0x13e/0x13e
>> > > > >  <srv> [24558.930239]  ? ioctl_preallocate+0x14e/0x14e
>> > > > >  <srv> [24558.930568]  ? SyS_rt_sigprocmask+0xf1/0x142
>> > > > >  <srv> [24558.930904]  ? sigprocmask+0x1d0/0x1d0
>> > > > >  <srv> [24558.931252]  SyS_ioctl+0x39/0x55
>> > > > >  <srv> [24558.931595]  ? do_vfs_ioctl+0xb10/0xb10
>> > > > >  <srv> [24558.931942]  do_syscall_64+0x1b1/0x31f
>> > > > >  <srv> [24558.932288]  entry_SYSCALL_64_after_hwframe+0x21/0x86
>> > > > >  <srv> [24558.932627] RIP: 0033:0x7f302849d8a7
>> > > > >  <srv> [24558.932965] RSP: 002b:00007f3029a52af8 EFLAGS: 00000206
>> > > > > ORIG_RAX:
>> > > > > 0000000000000010
>> > > > >  <srv> [24558.933578] RAX: ffffffffffffffda RBX: 00007f3027d861e3 RCX:
>> > > > > 00007f302849d8a7
>> > > > >  <srv> [24558.933927] RDX: 00007f3023f49468 RSI: 000000004004743a RDI:
>> > > > > 0000000000003a67
>> > > > >  <srv> [24558.934266] RBP: 00007f3029a52b20 R08: 0000000000000000 R09:
>> > > > > 000055c8308d8e40
>> > > > >  <srv> [24558.934607] R10: 0000000000000008 R11: 0000000000000206 R12:
>> > > > > 00007f3023f49358
>> > > > >  <srv> [24558.934947] R13: 00007ffe86e5723f R14: 0000000000000000 R15:
>> > > > > 00007f3029a53700
>> > > > >  <srv> [24558.935288]
>> > > > >  <srv> [24558.935626] Allocated by task 12622:
>> > > > >  <srv> [24558.935972]  ppp_register_net_channel+0x5f/0x5c6
>> > > > > [ppp_generic]
>> > > > >  <srv> [24558.936306]  pppoe_connect+0xab7/0xc71 [pppoe]
>> > > > >  <srv> [24558.936640]  SyS_connect+0x14b/0x1b7
>> > > > >  <srv> [24558.936975]  do_syscall_64+0x1b1/0x31f
>> > > > >  <srv> [24558.937319]  entry_SYSCALL_64_after_hwframe+0x21/0x86
>> > > > >  <srv> [24558.937655]
>> > > > >  <srv> [24558.937993] Freed by task 12622:
>> > > > >  <srv> [24558.938321]  kfree+0xb0/0x11d
>> > > > >  <srv> [24558.938658]  ppp_release+0x111/0x120 [ppp_generic]
>> > > > >  <srv> [24558.938994]  __fput+0x2ba/0x51a
>> > > > >  <srv> [24558.939332]  task_work_run+0x11c/0x13d
>> > > > >  <srv> [24558.939676]  exit_to_usermode_loop+0x7c/0xaf
>> > > > >  <srv> [24558.940022]  do_syscall_64+0x2ea/0x31f
>> > > > >  <srv> [24558.940368]  entry_SYSCALL_64_after_hwframe+0x21/0x86
>> > > > >  <srv> [24558.947099]
>> > > >
>> > > > Your first guess was right. It looks like we have an issue with
>> > > > reference counting on the channels. Can you send me your ppp_generic.o?
>> > > http://nuclearcat.com/ppp_generic.o
>> > > Compiled with gcc version 6.4.0 (Gentoo 6.4.0-r1 p1.3)
>> > >
>> > From what I can see, ppp_release() and ioctl(PPPIOCCONNECT) are called
>> > concurrently on the same ppp_file. Even if this ppp_file was pointed at
>> > by two different file descriptors, I can't see how this could defeat
>> > the reference counting mechanism. I'm going to think more about it.
>> >
>> > Can you test with CONFIG_REFCOUNT_FULL? (and keep
>> > d780cd44e3ce ("drivers, net, ppp: convert ppp_file.refcnt from
>> > atomic_t to refcount_t")).
>> Ok, i will try that tonight. On vanilla kernel or reversing mentioned 
>> in
>> previous email patch?
> On vanilla kernel. The other is really a shot in the dark.

As far as i can see there is only KASAN triggered again(and server 
rebooted shortly after that), but nothing else:

[ 1848.527234] 
==================================================================
[ 1848.527863] BUG: KASAN: use-after-free in ppp_ioctl+0xa68/0x14e7 
[ppp_generic]
[ 1848.528468] Write of size 8 at addr ffff880354d3fa38 by task 
accel-pppd/12626
[ 1848.528807]
[ 1848.529143] CPU: 5 PID: 12626 Comm: accel-pppd Tainted: G        W    
     4.15.3-build-0134 #2
[ 1848.529755] Hardware name: HP ProLiant DL320e Gen8 v2, BIOS P80 
04/02/2015
[ 1848.530100] Call Trace:
[ 1848.530448]  dump_stack+0x46/0x59
[ 1848.530793]  print_address_description+0x6b/0x23b
[ 1848.531143]  ? ppp_ioctl+0xa68/0x14e7 [ppp_generic]
[ 1848.531488]  kasan_report+0x21b/0x241
[ 1848.538248]  ppp_ioctl+0xa68/0x14e7 [ppp_generic]
[ 1848.538604]  ? ppp_nl_newlink+0x1da/0x1da [ppp_generic]
[ 1848.538949]  ? fsnotify+0x770/0x7fe
[ 1848.539295]  ? __fsnotify_inode_delete+0xc/0xc
[ 1848.539648]  ? kernel_read+0xed/0xed
[ 1848.539993]  ? memcpy+0x34/0x46
[ 1848.540332]  vfs_ioctl+0x6e/0x81
[ 1848.540679]  do_vfs_ioctl+0xa00/0xb10
[ 1848.541029]  ? __fsnotify_inode_delete+0xc/0xc
[ 1848.541375]  ? fcntl_setlk+0x6b8/0x6b8
[ 1848.541721]  ? ioctl_preallocate+0x14e/0x14e
[ 1848.542064]  ? rcu_is_watching+0x5/0x9
[ 1848.542404]  ? dput+0x4a/0x432
[ 1848.542739]  ? __fput+0x4e4/0x51a
[ 1848.543080]  SyS_ioctl+0x39/0x55
[ 1848.543418]  ? do_vfs_ioctl+0xb10/0xb10
[ 1848.543759]  do_syscall_64+0x1b1/0x31f
[ 1848.544100]  entry_SYSCALL_64_after_hwframe+0x21/0x86
[ 1848.544439] RIP: 0033:0x7f752170a8a7
[ 1848.544780] RSP: 002b:00007f7522cbfaf8 EFLAGS: 00000206 ORIG_RAX: 
0000000000000010
[ 1848.545403] RAX: ffffffffffffffda RBX: 00007f7520ff31e3 RCX: 
00007f752170a8a7
[ 1848.545752] RDX: 00007f7518cba868 RSI: 000000004004743a RDI: 
0000000000007c31
[ 1848.546097] RBP: 00007f7522cbfb20 R08: 0000000000000000 R09: 
000055ba01b29e40
[ 1848.546448] R10: 0000000073646172 R11: 0000000000000206 R12: 
00007f7518cba758
[ 1848.546802] R13: 00007ffe84df1a0f R14: 0000000000000000 R15: 
00007f7522cc0700
[ 1848.547148]
[ 1848.547490] Allocated by task 12626:
[ 1848.547834]  ppp_register_net_channel+0x5f/0x5c6 [ppp_generic]
[ 1848.548181]  pppoe_connect+0xab7/0xc71 [pppoe]
[ 1848.548535]  SyS_connect+0x14b/0x1b7
[ 1848.548878]  do_syscall_64+0x1b1/0x31f
[ 1848.549219]  entry_SYSCALL_64_after_hwframe+0x21/0x86
[ 1848.549562]
[ 1848.549901] Freed by task 12626:
[ 1848.550249]  kfree+0xb0/0x11d
[ 1848.550599]  ppp_release+0x112/0x121 [ppp_generic]
[ 1848.550941]  __fput+0x2ba/0x51a
[ 1848.551284]  task_work_run+0x11c/0x13d
[ 1848.551626]  exit_to_usermode_loop+0x7c/0xaf
[ 1848.551972]  do_syscall_64+0x2ea/0x31f
[ 1848.552322]  entry_SYSCALL_64_after_hwframe+0x21/0x86
[ 1848.552666]
[ 1848.553012] The buggy address belongs to the object at 
ffff880354d3f980
[ 1848.553012]  which belongs to the cache kmalloc-256 of size 256
[ 1848.553632] The buggy address is located 184 bytes inside of
[ 1848.553632]  256-byte region [ffff880354d3f980, ffff880354d3fa80)
[ 1848.554248] The buggy address belongs to the page:
[ 1848.554591] page:ffffea000d534f00 count:1 mapcount:0 mapping:         
  (null) index:0xffff880354d3f980 compound_mapcount: 0
[ 1848.555211] flags: 0x17ffe00000008100(slab|head)
[ 1848.555562] raw: 17ffe00000008100 0000000000000000 ffff880354d3f980 
000000010033002c
[ 1848.556174] raw: ffffea000d0f7420 ffffea000cf84d20 ffff8803f1c0f480 
0000000000000000
[ 1848.556783] page dumped because: kasan: bad access detected
[ 1848.557123]
[ 1848.557457] Memory state around the buggy address:
[ 1848.557800]  ffff880354d3f900: fb fb fb fb fb fb fb fb fc fc fc fc fc 
fc fc fc
[ 1848.558416]  ffff880354d3f980: fb fb fb fb fb fb fb fb fb fb fb fb fb 
fb fb fb
[ 1848.559028] >ffff880354d3fa00: fb fb fb fb fb fb fb fb fb fb fb fb fb 
fb fb fb
[ 1848.559643]                                         ^
[ 1848.559989]  ffff880354d3fa80: fc fc fc fc fc fc fc fc 00 00 00 00 00 
00 00 00
[ 1848.560603]  ffff880354d3fb00: 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00
[ 1848.561217] 
==================================================================
[ 1848.561830] Disabling lock debugging due to kernel taint

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