Re: [REGRESSION] in 3.18-rc1: ppp crashes kernel

[Takashi Iwai]

At Fri, 07 Nov 2014 12:10:46 +0100,
Stefan Seyfried wrote:
> 
> Hi all,
> 
> since 3.18-rc1, setting up a PPP interface kills my kernel with
> 
> [  163.433251] PPP generic driver version 2.4.2
> [  164.452474] ------------[ cut here ]------------
> [  164.453327] kernel BUG at ../mm/vmalloc.c:1316!
> [  164.453327] invalid opcode: 0000 [#1] PREEMPT SMP 
> [  164.453327] Modules linked in: ppp_async crc_ccitt ppp_generic slhc af_packet xfs libcrc32c coretemp kvm_intel 
> snd_hda_codec_conexant iTCO_wdt snd_hda_codec_generic iTCO_vendor_support uvcvideo snd_hda_intel snd_hda_controller mac80211 videobuf2_vmalloc snd_hda_codec kvm e1000e videobuf2_memops cfg80211 videobuf2_core v4l2_common snd_hwdep i2c_i801 videodev snd_pcm pcspkr thinkpad_acpi serio_raw wmi lpc_ich snd_timer thermal snd rfkill mfd_core tpm_tis shpchp mei_me soundcore ptp mei pps_core acpi_cpufreq tpm battery processor ac dm_mod btrfs xor raid6_pq i915 i2c_algo_bit drm_kms_helper drm video button sg
> [  164.453327] CPU: 0 PID: 6927 Comm: pppd Not tainted 3.18.0-rc3-3.ge706e91-desktop #1
> [  164.453327] Hardware name: LENOVO 7470E36/7470E36, BIOS 6DET61WW (3.11 ) 11/10/2009
> 
> This is easy to reproduce with:
> 
> linux:~ # cat bin/crashme.sh 
> ----
> #!/bin/bash -x
> pppd local pty "netcat -l 1234" &
> sleep 1
> pppd local pty "netcat localhost 1234" &
> sleep 1
> ----
> 
> 3.17 works fine.
> I bisected the issue multiple times and always arrived at
> 
> # first bad commit: [d6dd50e07c5bec00db2005969b1a01f8ca3d25ef] Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> 
> which is a merge commit unfortunately.
> 
> The BUG encountered above is in:
> 
> 1309 static struct vm_struct *__get_vm_area_node(unsigned long size,
> 1310                 unsigned long align, unsigned long flags, unsigned long start,
> 1311                 unsigned long end, int node, gfp_t gfp_mask, const void *caller)
> 1312 {
> 1313         struct vmap_area *va;
> 1314         struct vm_struct *area;
> 1315 
> 1316         BUG_ON(in_interrupt());
> 1317         if (flags & VM_IOREMAP)
> 1318                 align = 1ul << clamp(fls(size), PAGE_SHIFT, IOREMAP_MAX_ORDER);
> 1319 
> 
> the call trace is:
> [  164.453327] Call Trace:
> [  164.453327]  [<ffffffff811974bd>] __vmalloc_node_range+0x6d/0x290
> [  164.453327]  [<ffffffff8119771e>] __vmalloc+0x3e/0x50
> [  164.453327]  [<ffffffff81146950>] bpf_prog_alloc+0x30/0xa0
> [  164.453327]  [<ffffffff8157b716>] bpf_prog_create+0x46/0xb0
> [  164.453327]  [<ffffffffa07ecb90>] ppp_ioctl+0x420/0xe9a [ppp_generic]
> [  164.453327]  [<ffffffff811df1c7>] do_vfs_ioctl+0x2e7/0x4c0
> [  164.453327]  [<ffffffff811df421>] SyS_ioctl+0x81/0xa0
> [  164.453327]  [<ffffffff8165ee2d>] system_call_fastpath+0x16/0x1b
> [  164.453327]  [<00007f4502d87397>] 0x7f4502d87397

bpf_prog_create() is called inside spin_lock_bh(), and the BUG_ON()
hits.  Below is a quick fix.


Takashi

-- 8< --
From: Takashi Iwai <tiwai@xxxxxxx>
Subject: [PATCH] net: ppp: Don't call bpf_prog_create() in ppp_lock

In ppp_ioctl(), bpf_prog_create() is called inside ppp_lock, which
eventually calls vmalloc() and hits BUG_ON() in vmalloc.c.  This patch
works around the problem by moving the allocation outside the lock.

Reported-by: Stefan Seyfried <stefan.seyfried@xxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
 drivers/net/ppp/ppp_generic.c | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index 68c3a3f4e0ab..794a47329368 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -755,23 +755,23 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 		err = get_filter(argp, &code);
 		if (err >= 0) {
+			struct bpf_prog *pass_filter = NULL;
 			struct sock_fprog_kern fprog = {
 				.len = err,
 				.filter = code,
 			};
 
-			ppp_lock(ppp);
-			if (ppp->pass_filter) {
-				bpf_prog_destroy(ppp->pass_filter);
-				ppp->pass_filter = NULL;
+			err = 0;
+			if (fprog.filter)
+				err = bpf_prog_create(&pass_filter, &fprog);
+			if (!err) {
+				ppp_lock(ppp);
+				if (ppp->pass_filter)
+					bpf_prog_destroy(ppp->pass_filter);
+				ppp->pass_filter = pass_filter;
+				ppp_unlock(ppp);
 			}
-			if (fprog.filter != NULL)
-				err = bpf_prog_create(&ppp->pass_filter,
-						      &fprog);
-			else
-				err = 0;
 			kfree(code);
-			ppp_unlock(ppp);
 		}
 		break;
 	}
@@ -781,23 +781,23 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 		err = get_filter(argp, &code);
 		if (err >= 0) {
+			struct bpf_prog *active_filter = NULL;
 			struct sock_fprog_kern fprog = {
 				.len = err,
 				.filter = code,
 			};
 
-			ppp_lock(ppp);
-			if (ppp->active_filter) {
-				bpf_prog_destroy(ppp->active_filter);
-				ppp->active_filter = NULL;
+			err = 0;
+			if (fprog.filter)
+				err = bpf_prog_create(&active_filter, &fprog);
+			if (!err) {
+				ppp_lock(ppp);
+				if (ppp->active_filter)
+					bpf_prog_destroy(ppp->active_filter);
+				ppp->active_filter = active_filter;
+				ppp_unlock(ppp);
 			}
-			if (fprog.filter != NULL)
-				err = bpf_prog_create(&ppp->active_filter,
-						      &fprog);
-			else
-				err = 0;
 			kfree(code);
-			ppp_unlock(ppp);
 		}
 		break;
 	}
-- 
2.1.3

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