Subject: Re: ppp/pppoe, still panic 4.15.3 in ppp_push

From: Guillaume Nault <[email-masked]>
Date: Thu, 15 Feb 2018 16:55:17 +0100

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?