linux-kernel - Re: [PATCH] selinux: avc: mark avc node as not a leak

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Date:   Fri, 25 Jan 2019 03:26:54 +0530
From:   Prateek Patel <prpatel@...dia.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     <paul@...l-moore.com>, <sds@...ho.nsa.gov>,
        <eparis@...isplace.org>, <linux-kernel@...r.kernel.org>,
        <selinux@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <talho@...dia.com>, <swarren@...dia.com>, <linux-mm@...ck.org>,
        <snikam@...dia.com>, <vdumpa@...dia.com>
Subject: Re: [PATCH] selinux: avc: mark avc node as not a leak


On 1/9/2019 5:01 PM, Catalin Marinas wrote:
> Hi Prateek,
>
> On Wed, Jan 09, 2019 at 02:09:22PM +0530, Prateek Patel wrote:
>> From: Sri Krishna chowdary <schowdary@...dia.com>
>>
>> kmemleak detects allocated objects as leaks if not accessed for
>> default scan time. The memory allocated using avc_alloc_node
>> is freed using rcu mechanism when nodes are reclaimed or on
>> avc_flush. So, there is no real leak here and kmemleak_scan
>> detects it as a leak which is false positive. Hence, mark it as
>> kmemleak_not_leak.
> In theory, kmemleak should detect the node->rhead in the lists used by
> call_rcu() and not report it as a leak. Which RCU options do you have
> enabled (just to check whether kmemleak tracks the RCU internal lists)?
>
> Also, does this leak eventually disappear without your patch? Does
>
>    echo dump=0xffffffc0dd1a0e60 > /sys/kernel/debug/kmemleak
>
> still display this object?
>
> Thanks.
Hi Catalin,
It was intermittently showing leak and didn't repro on multiple runs. To 
repo, I decreased the
minimum object age for reporting, I found triggering the second scan 
just after first is not showing
any leak. Also, without my patch, on echo dump, obj is not displaying.
Is increasing minimum object age for reporting a good idea to handle 
such type of issues to
avoid false-positives?

Following is the log:

t186_int:/ # echo scan > /sys/kernel/debug/kmemleak
t186_int:/ # cat /sys/kernel/debug/kmemleak

unreferenced object 0xffffffc1e06424c8 (size 72):
   comm "netd", pid 4891, jiffies 4294906431 (age 23.120s)
   hex dump (first 32 bytes):
     97 01 00 00 1b 00 00 00 0b 00 00 00 57 06 04 00 ............W...
     00 00 00 00 ff ff ff ff 01 00 00 00 00 00 00 00 ................
   backtrace:
     [<ffffff8008275214>] kmem_cache_alloc+0x1ac/0x2c0
     [<ffffff80084dcf90>] avc_alloc_node+0x28/0x240
     [<ffffff80084dd404>] avc_compute_av+0xa4/0x1d0
     [<ffffff80084de1b8>] avc_has_perm+0xf8/0x1b8
     [<ffffff80084e37f8>] file_has_perm+0xb8/0xe8
     [<ffffff80084e3d64>] match_file+0x44/0x98
     [<ffffff80082cc9d4>] iterate_fd+0x84/0xd0
     [<ffffff80084e2b3c>] selinux_bprm_committing_creds+0xec/0x230
     [<ffffff80084d842c>] security_bprm_committing_creds+0x44/0x60
     [<ffffff80082ad020>] install_exec_creds+0x20/0x70
     [<ffffff800831b9a4>] load_elf_binary+0x31c/0xd10
     [<ffffff80082ae530>] search_binary_handler+0x98/0x288
     [<ffffff80082af078>] do_execveat_common.isra.14+0x550/0x6d0
     [<ffffff80082af4ac>] SyS_execve+0x4c/0x60
     [<ffffff80080839c0>] el0_svc_naked+0x34/0x38
     [<ffffffffffffffff>] 0xffffffffffffffff
unreferenced object 0xffffffc1ab3c61b0 (size 72):
   comm "crash_dump64", pid 5058, jiffies 4294907834 (age 17.508s)
   hex dump (first 32 bytes):
     2f 02 00 00 6b 00 00 00 07 00 00 00 53 04 04 00 /...k.......S...
     00 00 00 00 ff ff fd ff 01 00 00 00 00 00 00 00 ................
   backtrace:
     [<ffffff8008275214>] kmem_cache_alloc+0x1ac/0x2c0
     [<ffffff80084dcf90>] avc_alloc_node+0x28/0x240
     [<ffffff80084dd404>] avc_compute_av+0xa4/0x1d0
     [<ffffff80084de084>] avc_has_perm_noaudit+0xe4/0x120
     [<ffffff80084e1264>] selinux_inode_permission+0xc4/0x1c8
     [<ffffff80084d8fe8>] security_inode_permission+0x60/0x88
     [<ffffff80082b2cf4>] __inode_permission2+0x54/0x120
     [<ffffff80082b2e30>] inode_permission2+0x38/0x80
     [<ffffff80082b4b58>] may_open+0x70/0x128
     [<ffffff80082b6fd4>] do_last+0x234/0xee8
     [<ffffff80082b7d30>] path_openat+0xa8/0x310
     [<ffffff80082b9390>] do_filp_open+0x88/0x108
     [<ffffff80082a1fec>] do_sys_open+0x1a4/0x290
     [<ffffff80082a215c>] SyS_openat+0x3c/0x50
     [<ffffff80080839c0>] el0_svc_naked+0x34/0x38
     [<ffffffffffffffff>] 0xffffffffffffffff
unreferenced object 0xffffffc1d3bcf678 (size 72):
   comm "mediaserver", pid 5156, jiffies 4294909577 (age 10.536s)
   hex dump (first 32 bytes):
     0b 02 00 00 e2 01 00 00 07 00 00 00 53 04 04 00 ............S...
     00 00 00 00 f7 ff ff ff 01 00 00 00 00 00 00 00 ................
   backtrace:
     [<ffffff8008275214>] kmem_cache_alloc+0x1ac/0x2c0
     [<ffffff80084dcf90>] avc_alloc_node+0x28/0x240
     [<ffffff80084dd404>] avc_compute_av+0xa4/0x1d0
     [<ffffff80084de084>] avc_has_perm_noaudit+0xe4/0x120
     [<ffffff80084e1264>] selinux_inode_permission+0xc4/0x1c8
     [<ffffff80084d8fe8>] security_inode_permission+0x60/0x88
     [<ffffff80082b2cf4>] __inode_permission2+0x54/0x120
     [<ffffff80082b2e30>] inode_permission2+0x38/0x80
     [<ffffff80082b4b58>] may_open+0x70/0x128
     [<ffffff80082b6fd4>] do_last+0x234/0xee8
     [<ffffff80082b7d30>] path_openat+0xa8/0x310
     [<ffffff80082b9390>] do_filp_open+0x88/0x108
     [<ffffff80082a1fec>] do_sys_open+0x1a4/0x290
     [<ffffff80082a21f4>] compat_SyS_openat+0x3c/0x50
     [<ffffff80080839c0>] el0_svc_naked+0x34/0x38
     [<ffffffffffffffff>] 0xffffffffffffffff
t186_int:/ # echo dump=0xffffffc1d3bcf678 > /sys/kernel/debug/kmemleak
kmemleak: Unknown object at 0xffffffc1d3bcf678

Thanks,