Messages in this thread Patch in this message | | | Date | Wed, 09 Feb 2011 21:48:57 -0800 (PST) | Subject | Re: Linux 2.6.38-rc4 (other bugs: x25) | From | David Miller <> |
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From: Randy Dunlap <randy.dunlap@oracle.com> Date: Wed, 9 Feb 2011 20:58:42 -0800
> Here's what I captured before the system hung and the beeper stayed > on constantly. ;)
:-)
> [ 303.931229] general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC > [ 303.934923] last sysfs file: /sys/devices/pci0000:00/0000:00:1d.1/usb6/6-1/6-1.3/devnum > [ 303.934923] CPU 1 > [ 303.934923] Modules linked in: x25(-) af_packet nfsd lockd nfs_acl auth_rpcgss exportfs sunrpc ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 iptable_filter ip_tables ip6t_REJECT xt_tcpudp nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables x_tables ipv6 cpufreq_ondemand acpi_cpufreq freq_table mperf binfmt_misc dm_mirror dm_region_hash dm_log dm_multipath scsi_dh dm_mod joydev mousedev evdev mac_hid snd_hda_codec_analog snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device usbmouse usbkbd usbhid snd_pcm hid snd_timer sr_mod tg3 pcspkr rtc_cmos dcdbas sg snd iTCO_wdt cdrom i2c_i801 rtc_core processor iTCO_vendor_support rtc_lib 8250_pnp soundcore thermal_sys intel_agp button intel_gtt snd_page_alloc hwmon unix ide_pci_generic ide_core ata_generic pata_acpi ata_piix sd_mod crc_t10dif ext3 jbd mbcache uhci_hcd ohci_hcd ssb mmc_core pcmcia pcmcia_core firmware_class ehci_hcd usbcore nls_base [last unloaded: microcode] > [ 303.934923] > [ 303.934923] Pid: 2573, comm: rmmod Not tainted 2.6.38-rc4 #3 0TY565/OptiPlex 745 > [ 303.934923] RIP: 0010:[<ffffffffa069c131>] [<ffffffffa069c131>] x25_link_free+0x41/0x81 [x25]
Ok, a GPF in x25_link_free().
This code simply traverses the x25_neigh_list, unlinking and releasing each entry it finds.
Every node entry which is added to this list is dynamically allocated entry. See x25_link_device_up(), which is the only place where a list_add() is performed on the x25_neigh_list.
The device should be accessible and the dev_put() should not cause trouble because we grabbed a reference to this device when x25_link_device_up() added the new x25_neigh to the list.
I can't see anything here that should barf like this.
I also can't see anything "const" in the x25 protocol code that might be trampled upon.
I'm assuming in all of this that it's a write to a read-only location which is causing this GPF, via CONFIG_DEBUG_RODATA.
Playing around with config options and looking at the various x86_64 asm in these different cases seems to suggest that it's indeed the dev_put() that is causing the GPF.
Network devices use per-cpu refcounts.
We know that at some point in the past, the ref bump worked, because we did a dev_hold() when we added the referencing x25_neigh entry to the list.
For some reason now it fails.
RAX is where the per-cpu base pointer should be, and in your dump that's:
[ 303.934923] RAX: 6b6b6b6b6b6b6b6b RBX: ffffffffa06a03d0 RCX: 0010000000004040
Which is the SLAB free poison value.
So it seems like the network device at nb->dev has been freed for some reason.
Weird....
Oh, the bug is obvious... 'nb' is freed right before we 'nb->dev', duh.
Please try this fix:
-------------------- x25: Do not reference freed memory.
In x25_link_free(), we destroy 'nb' before dereferencing 'nb->dev'. Don't do this, because 'nb' might be freed by then.
Reported-by: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net> --- net/x25/x25_link.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/net/x25/x25_link.c b/net/x25/x25_link.c index 4cbc942..2130692 100644 --- a/net/x25/x25_link.c +++ b/net/x25/x25_link.c @@ -396,9 +396,12 @@ void __exit x25_link_free(void) write_lock_bh(&x25_neigh_list_lock); list_for_each_safe(entry, tmp, &x25_neigh_list) { + struct net_device *dev; + nb = list_entry(entry, struct x25_neigh, node); + dev = nb->dev; __x25_remove_neigh(nb); - dev_put(nb->dev); + dev_put(dev); } write_unlock_bh(&x25_neigh_list_lock); } -- 1.7.4
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