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Re: Occasional memory fault in inode_has_perm() while running xfstest 23

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: Occasional memory fault in inode_has_perm() while running xfstest 234
From: Eric Paris <eparis@xxxxxxxxxxxxxx>
Date: Mon, 14 Nov 2011 10:13:11 -0500
Cc: Chandra Seetharaman <sekharan@xxxxxxxxxx>, XFS Mailing List <xfs@xxxxxxxxxxx>, linux-security-module@xxxxxxxxxxxxxxx
In-reply-to: <20111114102755.GA31043@xxxxxxxxxxxxx>
References: <1320961003.2201.27.camel@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20111114102755.GA31043@xxxxxxxxxxxxx>
The only way this can happen is if the filesystem is creating inodes
and not calling security_inode_alloc() (which should be done in
inode_init_always)

I can only guess (and believe me it is a complete wild guess after
looking at grep for 5 seconds) it has something to do with the XFS
__releases() function which does some weirdness in the case of a
failed call to inode_init_always().

The only other option is an FS somehow still uses an inode after
__destroy_inode(), but I'd assume that would land you in other
troubles.  In either case, I'm hard pressed to blame SELinux/LSM,
since the VFS does appear to be hooked in the right places
(inode_init_alwasys and __destroy_inode) to set and unset
inode->i_security....

-Eric

On Mon, Nov 14, 2011 at 5:27 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> This looks like a selinux issues.  Ccing the LSM list.
>
> On Thu, Nov 10, 2011 at 03:36:43PM -0600, Chandra Seetharaman wrote:
>> Hi All,
>>
>> While debugging the xfstest case 234, I was occasionally hitting the
>> following memory fault. Has anybody seen it ?
>>
>> -----------------
>> IP: [<ffffffff811e57ff>] inode_has_perm+0x1f/0x40
>> PGD 0
>> Oops: 0000 [#1] SMP
>> CPU 0
>> Modules linked in: xfs exportfs ebtable_nat ebtables ipt_MASQUERADE 
>> iptable_nat nf_nat iptable_mangle bridge stp llc autofs4 sunrpc 
>> cpufreq_ondemand acpi_cpufreq freq_table mperf ipt_REJECT nf_conntrack_ipv4 
>> nf_defrag_ipv4 iptable_filter ip_tables ip6t_REJECT nf_conntrack_ipv6 
>> nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables ipv6 ext3 
>> jbd dm_mirror dm_region_hash dm_log dm_mod vhost_net macvtap macvlan tun 
>> kvm_intel kvm cdc_ether usbnet mii microcode serio_raw i2c_i801 i2c_core 
>> iTCO_wdt iTCO_vendor_support shpchp ioatdma i7core_edac edac_core ses 
>> enclosure sg igb dca ext4 mbcache jbd2 sd_mod crc_t10dif ahci libahci 
>> megaraid_sas [last unloaded: scsi_wait_scan]
>>
>> Pid: 32611, comm: setquota Not tainted 3.1.0-rc9.virgin+ #6 IBM  System 
>> x3630 M3 -[7377AC1]-/69Y1101
>> RIP: 0010:[<ffffffff811e57ff>]  [<ffffffff811e57ff>] inode_has_perm+0x1f/0x40
>> RSP: 0018:ffff880642bcdb78  EFLAGS: 00010246
>> RAX: 0000000000800002 RBX: ffff88064f2205f8 RCX: 0000000000800000
>> RDX: 0000000000800000 RSI: 0000000000000000 RDI: ffff880649e58480
>> RBP: ffff880642bcdb78 R08: ffff880642bcdb88 R09: 0000000000000080
>> R10: ffff880658ffff00 R11: ffff880642bcdb88 R12: 0000000000000081
>> R13: ffff88064f2205f8 R14: ffff8806592b8100 R15: 0000000000000000
>> FS:  00007f56dfa3a700(0000) GS:ffff88067f200000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> CR2: 0000000000000020 CR3: 0000000642b30000 CR4: 00000000000006f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>> Process setquota (pid: 32611, threadinfo ffff880642bcc000, task 
>> ffff8806592b8100)
>> Stack:
>> ffff880642bcdc18 ffffffff811e5d79 0000000000000009 0000000000000000
>> ffff88064f2205f8 0000000000000000 0000000000000000 0000000000000000
>> 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>> Call Trace:
>> [<ffffffff811e5d79>] selinux_inode_permission+0xa9/0x100
>> [<ffffffff811e323c>] security_inode_permission+0x1c/0x30
>> [<ffffffff81162509>] inode_permission+0x49/0x100
>> [<ffffffff81164b57>] link_path_walk+0x87/0x810
>> [<ffffffff810fedfa>] ? unlock_page+0x2a/0x40
>> [<ffffffff81165955>] path_lookupat+0x55/0x690
>> [<ffffffff81125867>] ? handle_pte_fault+0xf7/0xb50
>> [<ffffffff81165fc1>] do_path_lookup+0x31/0xc0
>> [<ffffffff81162168>] ? getname_flags+0x1f8/0x280
>> [<ffffffff81166df9>] user_path_at+0x59/0xa0
>> [<ffffffff8112641b>] ? handle_mm_fault+0x15b/0x270
>> [<ffffffff814af8c0>] ? do_page_fault+0x1e0/0x460
>> [<ffffffff81146a62>] ? kmem_cache_alloc+0x152/0x190
>> [<ffffffff8115b9c7>] vfs_fstatat+0x47/0x80
>> [<ffffffff81077571>] ? do_sigaction+0x91/0x1d0
>> [<ffffffff8115badb>] vfs_stat+0x1b/0x20
>> [<ffffffff8115bb04>] sys_newstat+0x24/0x50
>> [<ffffffff810c3c4f>] ? audit_syscall_entry+0x1bf/0x1f0
>> [<ffffffff814b29c2>] system_call_fastpath+0x16/0x1b
>> Code: 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 66 66 66 66 90 f6 46 
>> 0d 02 75 23 48 8b 76 38 48 8b 7f 68 45 89 c1 49 89 c8 89 d1 <0f> b7 46 20 8b 
>> 7f 04 8b 76 1c 89 c2 e8 a0 f9 ff ff c9 c3 31 c0
>> RIP  [<ffffffff811e57ff>] inode_has_perm+0x1f/0x40
>> RSP <ffff880642bcdb78>
>> CR2: 0000000000000020
>> ---[ end trace 5d054c892d311b3f ]---
>> ----------------------------
>>
>> I made some code changes and found that inode->i_security is the data
>> structure that is NULL.
>>
>> I added the following code
>> ------------------
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 266a229..43870ec 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -1466,6 +1466,7 @@ static int task_has_system(struct task_struct *tsk,
>>                           SECCLASS_SYSTEM, perms, NULL);
>>  }
>>
>> +u64 isec_yes;
>>  /* Check whether a task has a particular permission to an inode.
>>     The 'adp' parameter is optional and allows other audit
>>     data to be passed (e.g. the dentry). */
>> @@ -1486,6 +1487,13 @@ static int inode_has_perm(const struct cred *cred,
>>       sid = cred_sid(cred);
>>       isec = inode->i_security;
>>
>> +     if (isec)
>> +             isec_yes++;
>> +     else {
>> +             printk("isec NULL; isec_yes %llu\n", isec_yes);
>> +             return -EACCES;
>> +     }
>> +
>>       return avc_has_perm_flags(sid, isec->sid, isec->sclass, perms, adp, 
>> flags);
>>  }
>>
>> --------------------------------
>>
>> and this is what I see in /var/log/messages
>> -----------------------------
>> isec NULL; isec_yes 14345860
>> isec NULL; isec_yes 102846678
>> isec NULL; isec_yes 107203361
>> isec NULL; isec_yes 136859591
>> isec NULL; isec_yes 140941549
>> isec NULL; isec_yes 168163633
>> isec NULL; isec_yes 222030886
>> isec NULL; isec_yes 238835570
>> isec NULL; isec_yes 263587444
>> isec NULL; isec_yes 280912141
>> ------------------------------
>>
>> Can somebody throw some light on it ?
>>
>> I am using xfs.sgi.com with commit 9e4c109ac822395e0aae650e4e3c9e4903f6602f
>> at the top.
>>
>> Regards,
>>
>> Chandra
>>
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