On Mon, Jul 24, 2017 at 08:21:16PM -0700, Kees Cook wrote:
On Mon, Jul 24, 2017 at 6:03 AM, Hans Liljestrand
<[email protected]> wrote:
On Sun, Jul 23, 2017 at 08:52:53PM -0700, Kees Cook wrote:
Is 14afee4b6092f ("net: convert sock.sk_wmem_alloc from atomic_t to
refcount_t") correct? That looks like a statistics counter, not a
refcounter? I can't quite tell, though...
Hmm, yes, it looks a bit weird, but it is used in a refcount fashion here:
void sk_free(struct sock *sk)
{
/*
* We subtract one from sk_wmem_alloc and can know if
* some packets are still in some tx queue.
* If not null, sock_wfree() will call __sk_free(sk) later
*/
if (refcount_dec_and_test(&sk->sk_wmem_alloc))
__sk_free(sk);
}
http://elixir.free-electrons.com/linux/v4.13-rc1/source/net/core/sock.c#L1605
Ah yeah, there it is. Hrmpf. Something is triggering WARNs, though...
I wonder if this can get examined more closely?
I tried reproducing the error but I don't seem to know how to use lkp. Got
lots of permission denied errors and finally ran out of disk space (after
using up ~50GB).
Maybe I did something wrong?
What I did was: Cloned the related kernel repository, checked out offending
commit, plopped in config, compiled bzImage. Then I just cloned the lkp repo
and tried running the provided command line with the bzImage and provided
script.
I'll take another look once I have the time, might be I missed something
earlier.
Also, why not atomic->refcount for sk_rmem_alloc?
I couldn't find any similar refcount-like use on sk_rmem_alloc.
And as noted the sk_wmem_alloc thing is also a bit dubious. It looks like it
serves a dual purpose of actual allocation size and occasional reference
counter.
Regards,
-hans
-Kees
And here:
if (refcount_sub_and_test(len, &sk->sk_wmem_alloc))
__sk_free(sk);
}
http://elixir.free-electrons.com/linux/v4.13-rc1/source/net/core/sock.c#L1798
I think this WARN is from:
WARN_ON(refcount_read(&sk->sk_wmem_alloc));
I looked through the commit and couldn't find any direct conversion issues.
Although I guess it is debatable whether refcoun_t should be used in this
kind of less conventional case.
The only potential problem I noticed was that based on the following change
(or rather the original code) it seems like sk_wmem_alloc could sometimes be
negative. I'm not familiar enough with the code to say whether that really
is the case.
--- a/drivers/atm/fore200e.c
+++ b/drivers/atm/fore200e.c
@@ -924,12 +924,7 @@ fore200e_tx_irq(struct fore200e* fore200e)
else {
dev_kfree_skb_any(entry->skb);
}
-#if 1
- /* race fixed by the above incarnation mechanism, but... */
- if (atomic_read(&sk_atm(vcc)->sk_wmem_alloc) < 0) {
- atomic_set(&sk_atm(vcc)->sk_wmem_alloc, 0);
- }
-#endif
+
/* check error condition */
if (*entry->status & STATUS_ERROR)
atomic_inc(&vcc->stats->tx_err);
But if this is actually supposed to legitimately happen and eventually
"balance out" refcount_t might not work here. On the other hand this should
have triggered an earlier WARN_ON already, so it doesn't seem to be the
issue here?
Regards,
-hans
-Kees
On Sun, Jul 23, 2017 at 7:13 PM, kernel test robot
<[email protected]> wrote:
FYI, we noticed the following commit:
commit: b631e535c61d7ddbb7ebac545f729ca9b3b6d70e ("x86/refcount:
Implement fast refcount overflow protection")
https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git
kspp/fast-refcount/ud/v6
in testcase: boot
on test machine: qemu-system-x86_64 -enable-kvm -smp 2 -m 512M
caused below changes (please refer to attached dmesg/kmsg for entire
log/backtrace):
+------------------------------------------------------------+------------+------------+
| | 561ee9566e
| b631e535c6 |
+------------------------------------------------------------+------------+------------+
| boot_successes | 37
| 0 |
| boot_failures | 0
| 4 |
| WARNING:at_net/netlink/af_netlink.c:#netlink_sock_destruct | 0
| 4 |
+------------------------------------------------------------+------------+------------+
[ 36.991339] WARNING: CPU: 0 PID: 280 at net/netlink/af_netlink.c:374
netlink_sock_destruct+0x1ea/0x200
[ 36.994035] Modules linked in:
[ 36.994815] CPU: 0 PID: 280 Comm: sh Not tainted
4.13.0-rc1-00003-gb631e53 #1
[ 36.996546] task: ffff88001448c180 task.stack: ffffc900004e0000
[ 36.998006] RIP: 0010:netlink_sock_destruct+0x1ea/0x200
[ 36.999290] RSP: 0018:ffffffff82433de0 EFLAGS: 00010206
[ 37.000591] RAX: ffff88001448c180 RBX: ffff880016a3d000 RCX:
0000000000000000
[ 37.002319] RDX: 0000000000000100 RSI: 0000000000000001 RDI:
ffffffff82796f48
[ 37.004061] RBP: ffffffff82433df0 R08: 0000000000000000 R09:
0000000000000000
[ 37.005780] R10: 0000000000000001 R11: 0000000000000001 R12:
0000000000000001
[ 37.007528] R13: ffffffff81cd4a00 R14: 96e49674e09954cf R15:
000000000000001f
[ 37.009261] FS: 0000000000000000(0000) GS:ffffffff82430000(0000)
knlGS:0000000000000000
[ 37.011233] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 37.012629] CR2: 00007f268a96e688 CR3: 00000000159ff000 CR4:
00000000000006b0
[ 37.014212] Call Trace:
[ 37.014745] <IRQ>
[ 37.015201] __sk_destruct+0x3a2/0x4c0
[ 37.015994] sk_destruct+0x3f/0x70
[ 37.016747] __sk_free+0x10d/0x160
[ 37.017479] sk_free+0x4a/0x60
[ 37.018127] deferred_put_nlk_sk+0xd9/0xf0
[ 37.018998] rcu_process_callbacks+0x766/0x1cb0
[ 37.019944] ? rcu_process_callbacks+0x643/0x1cb0
[ 37.020960] __do_softirq+0x10c/0x6b2
[ 37.021749] irq_exit+0x135/0x140
[ 37.022458] smp_apic_timer_interrupt+0x3b/0x50
[ 37.023429] apic_timer_interrupt+0x8e/0xa0
[ 37.024303] RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x60
[ 37.025141] RSP: 0018:ffffc900004e3c10 EFLAGS: 00000246 ORIG_RAX:
ffffffffffffff10
[ 37.026605] RAX: ffff88001448c180 RBX: ffffffff82727288 RCX:
0000000000000000
[ 37.028340] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
ffffffff82727288
[ 37.030077] RBP: ffffc900004e3c60 R08: 0000000000000000 R09:
0000000000000000
[ 37.031796] R10: 0000000000000000 R11: 0000000000000001 R12:
0000000000000000
[ 37.033546] R13: 0000000000000000 R14: 0000000000000000 R15:
00007f2689f93000
[ 37.035262] </IRQ>
[ 37.035814] ? ftrace_likely_update+0x39/0x200
[ 37.036925] ? vm_normal_page+0xd7/0x1a0
[ 37.037886] unmap_page_range+0x775/0x14d0
[ 37.038658] unmap_single_vma+0x158/0x180
[ 37.039403] unmap_vmas+0x5b/0x80
[ 37.040202] exit_mmap+0x118/0x220
[ 37.040900] mmput+0xd5/0x240
[ 37.041479] do_exit+0xdb6/0x16d0
[ 37.042183] ? entry_SYSCALL_64_fastpath+0x5/0xbd
[ 37.043365] do_group_exit+0x8a/0x160
[ 37.044282] SyS_exit_group+0x1d/0x20
[ 37.045192] entry_SYSCALL_64_fastpath+0x1f/0xbd
[ 37.046321] RIP: 0033:0x7f268a676408
[ 37.047221] RSP: 002b:00007ffcba052ea8 EFLAGS: 00000246 ORIG_RAX:
00000000000000e7
[ 37.049042] RAX: ffffffffffffffda RBX: 000000000000007f RCX:
00007f268a676408
[ 37.050784] RDX: 000000000000007f RSI: 000000000000003c RDI:
000000000000007f
[ 37.052512] RBP: 00007f268a96e688 R08: 00000000000000e7 R09:
ffffffffffffffa0
[ 37.054281] R10: 0000000000000000 R11: 0000000000000246 R12:
00007f268a96ff40
[ 37.056004] R13: 0000000000000001 R14: 0000000000000000 R15:
00000000ffffffff
[ 37.057765] Code: e8 56 14 48 ff eb ca e8 b5 42 4f ff 0f ff 0f 1f 00
eb a7 e8 a9 42 4f ff 0f ff 0f 1f 80 00 00 00 00 e9 48 ff ff ff e8 96 42 4f
ff <0f> ff 0f 1f 40 00 e9 e5 fe ff ff 90 66 2e 0f 1f 84 00 00 00 00
[ 37.062621] ---[ end trace db04ba531557bbda ]---
To reproduce:
git clone https://github.com/01org/lkp-tests.git
cd lkp-tests
bin/lkp qemu -k <bzImage> job-script # job-script is attached in
this email
Thanks,
Xiaolong
--
Kees Cook
Pixel Security
--
Kees Cook
Pixel Security
