On Thu, Sep 6, 2012 at 8:16 AM, Dave Jones <da...@redhat.com> wrote: > On Thu, Sep 06, 2012 at 09:46:28AM -0400, Dave Jones wrote: > > Hit this in overnight fuzz testing.. > > > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000020 > > IP: [<ffffffff81103365>] audit_log_d_path+0x35/0xf0 > > PGD 12fded067 PUD 142c06067 PMD 0 > > Oops: 0000 [#1] SMP > > Modules linked in: tun fuse ipt_ULOG binfmt_misc nfnetlink nfc caif_socket > caif phonet can llc2 pppoe pppox ppp_generic slhc irda crc_ccitt rds af_key > decnet rose x25 atm netrom appletalk ipx p8023 psnap p8022 llc ax25 lockd > sunrpc bluetooth rfkill ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 > ip6table_filter ip6_tables nf_conntrack_ipv4 nf_defrag_ipv4 xt_state > nf_conntrack kvm_intel kvm crc32c_intel ghash_clmulni_intel microcode pcspkr > i2c_i801 e1000e uinput i915 video i2c_algo_bit drm_kms_helper drm i2c_core > > CPU 5 > > Pid: 7007, comm: trinity-child5 Not tainted 3.6.0-rc4+ #36 > > RIP: 0010:[<ffffffff81103365>] [<ffffffff81103365>] > audit_log_d_path+0x35/0xf0 > > RSP: 0018:ffff880116b33ec8 EFLAGS: 00010246 > > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000035 > > RDX: ffffffff819dbf5d RSI: ffffffff819da5bb RDI: 0000000000000000 > > RBP: ffff880116b33ee8 R08: ffff88001942533e R09: 0000000000000000 > > R10: 0000000000000001 R11: 0000000000000000 R12: ffff880116b33f38 > > R13: ffff880116b33f38 R14: ffffffff819fa1eb R15: 0000000000000005 > > FS: 00007f5742581740(0000) GS:ffff880148600000(0000) > knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000000000000020 CR3: 00000001046d3000 CR4: 00000000001407e0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > > Process trinity-child5 (pid: 7007, threadinfo ffff880116b32000, task > ffff880019424d00) > > Stack: > > ffff880116b33ee8 0000000000000000 ffff880116b33f38 ffff880019424d00 > > ffff880116b33f18 ffffffff81103522 00000000000001d0 ffff880119ed6500 > > 00000000000001d0 0000000000000109 ffff880116b33f78 ffffffff811ebb95 > > Call Trace: > > [<ffffffff81103522>] audit_log_link_denied+0x92/0x100 > > [<ffffffff811ebb95>] sys_linkat+0x195/0x1e0 > > [<ffffffff813573de>] ? trace_hardirqs_on_thunk+0x3a/0x3f > > [<ffffffff816a50ed>] system_call_fastpath+0x1a/0x1f > > Code: 5d e8 4c 89 65 f0 4c 89 6d f8 0f 1f 44 00 00 48 85 f6 48 89 fb 49 89 > d5 74 11 48 89 f2 31 c0 48 c7 c6 bb a5 9d 81 e8 8b e1 ff ff <8b> 73 20 40 f6 > c6 01 75 62 48 8b 3d 33 33 93 01 48 85 ff 74 4e > > RIP [<ffffffff81103365>] audit_log_d_path+0x35/0xf0 > > RSP <ffff880116b33ec8> > > CR2: 0000000000000020 > > ---[ end trace 85b88c850143bb1c ]--- > > > > That's here in kernel/audit.c > > > > 1433 > > 1434 /* We will allow 11 spaces for ' (deleted)' to be appended */ > > 1435 pathname = kmalloc(PATH_MAX+11, ab->gfp_mask); > > > > 'ab' is NULL. > > > > Looks like audit_log_link_denied needs to handle potential failure from > > audit_log_start and abort early. (oddly, it looks like every other > > function called there checks for !ab.) > > > > Maybe additional code should be added here to printk the audit message > > to dmesg so that we don't lose it entirely, but for now, minimal fix. > > > > Signed-off-by: Dave Jones <da...@redhat.com> > > > > diff --git a/kernel/audit.c b/kernel/audit.c > > index ea3b7b6..c3e85bb 100644 > > --- a/kernel/audit.c > > +++ b/kernel/audit.c > > @@ -1466,6 +1466,9 @@ void audit_log_link_denied(const char *operation, > struct path *link) > > > > ab = audit_log_start(current->audit_context, GFP_KERNEL, > > AUDIT_ANOM_LINK); > > + if (!ab) > > + return; > > + > > audit_log_format(ab, "op=%s action=denied", operation); > > audit_log_format(ab, " pid=%d comm=", current->pid); > > audit_log_untrustedstring(ab, current->comm);
This fix looks fine to me. > Added Kees, as this was introduced in a51d9eaa41866ab6b4b6ecad7b621f8b66ece0dc > > I just realised, the funny thing about this is that the machine running that > test > had selinux/audit disabled. And yet here we are, screwing around with audit > buffers. The intent was to have this message show up in dmesg even if auditd wasn't running, and even if the specific process wasn't being explicitly audited. > Should there be a test on audit_enable=0 in audit_log_link_denied() ? > > I'm now curious how much more of the audit code is getting run through > similar lack of tests What is the condition in which audit_log_start fails? -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/