linux-kernel - Re: [kmemleak] unreferenced object 0xcd9c1a80 (size 192):

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Message-ID: <609d04c4-f947-ede5-3c4f-28eaf0b14745@iogearbox.net>
Date:   Mon, 12 Feb 2018 09:28:33 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Yonghong Song <yhs@...com>, Mathieu Malaterre <malat@...ian.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [kmemleak] unreferenced object 0xcd9c1a80 (size 192):

On 02/12/2018 06:47 AM, Yonghong Song wrote:
> On 2/11/18 11:18 AM, Mathieu Malaterre wrote:
>> On Sun, Feb 11, 2018 at 5:54 PM, Alexei Starovoitov
>> <alexei.starovoitov@...il.com> wrote:
>>> On Sun, Feb 11, 2018 at 7:24 AM, Mathieu Malaterre <malat@...ian.org> wrote:
>>>> Alexei,
>>>>
>>>> Could you please comment on why I am seeing those memleaks being
>>>> reported on my ppc32 system ? Should they be marked as false positive
>>>> ?
>>>>
>>>> System is Mac Mini G4, git/master (4.15.0+), ppc.
>>>>
>>>> Thanks for your time
>>>>
>>>> $ dmesg
>>>> ...
>>>> [ 1281.504173] kmemleak: 36 new suspected memory leaks (see
>>>> /sys/kernel/debug/kmemleak)
>>>>
>>>> Where:
>>>>
>>>> # cat /sys/kernel/debug/kmemleak
>>>> unreferenced object 0xdee25000 (size 192):
>>>>    comm "systemd", pid 1, jiffies 4294894348 (age 1438.580s)
>>>>    hex dump (first 32 bytes):
>>>>      c0 56 2f 88 00 00 00 00 00 00 00 0b 00 00 00 0c  .V/.............
>>>>      00 00 00 08 00 00 00 01 00 00 00 01 00 00 00 01  ................
>>>>    backtrace:
>>>>      [<6c69baf5>] trie_alloc+0xb0/0x150
>>>>      [<fa093284>] SyS_bpf+0x288/0x1458
>>>>      [<82182f53>] ret_from_syscall+0x0/0x38
>>>> unreferenced object 0xdee25900 (size 192):
>>>>    comm "systemd", pid 1, jiffies 4294894540 (age 1437.812s)
>>>>    hex dump (first 32 bytes):
>>>>      c0 56 2f 88 00 00 00 00 00 00 00 0b 00 00 00 08  .V/.............
>>>>      00 00 00 08 00 00 00 01 00 00 00 01 00 00 00 01  ................
>>>>    backtrace:
>>>>      [<6c69baf5>] trie_alloc+0xb0/0x150
>>>>      [<fa093284>] SyS_bpf+0x288/0x1458
>>>>      [<82182f53>] ret_from_syscall+0x0/0x38
>>>
>>> hmm. looks real. Is there a reproducer?
>>> Yonghong, lpm map not cleaning after itself?
>>
>> Not really. I simply boot up my machine and wait for the first kmemleak scan.
> 
> I am not able to reproduce the issue. Tried with latest net-next on FC26 with kmemleak on. I only got this one after bootup,
> 'cat /sys/kernel/debug/kmemleak' or
> 'echo scan > /sys/kernel/debug/kmemleak
>  cat /sys/kernel/debug/kmemleak':
> 
> unreferenced object 0xffff99701a7386e0 (size 32):
>   comm "mount", pid 1856, jiffies 4294669263 (age 98.440s)
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<000000004668ec00>] security_sb_parse_opts_str+0x36/0x50
>     [<00000000a9807d2b>] parse_security_options+0x3d/0x60
>     [<00000000cc1e1d58>] btrfs_mount_root+0x139/0x720
>     [<00000000bdc4f1a3>] mount_fs+0x30/0x150
>     [<00000000f189f1bd>] vfs_kern_mount.part.26+0x54/0x100
>     [<0000000093ae5db7>] btrfs_mount+0x184/0x914
>     [<00000000bdc4f1a3>] mount_fs+0x30/0x150
>     [<00000000f189f1bd>] vfs_kern_mount.part.26+0x54/0x100
>     [<000000003b67b9fc>] do_mount+0x5b9/0xc70
>     [<00000000de4073a0>] SyS_mount+0x80/0xd0
>     [<00000000fc5a968a>] do_syscall_64+0x5d/0x110
>     [<000000003d61f5fc>] entry_SYSCALL_64_after_hwframe+0x21/0x86
>     [<00000000458a6ffa>] 0xffffffffffffffff
> 
> Not sure whether the above is a true issue or not.
> 
> However, by inspecting the code, I do find the trie_free in lpm_trie.c
> may have missed freeing the trie memory.
> 
> The change likes below should work:
> -bash-4.2$ git diff
> diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
> index 7b469d1..cecb259 100644
> --- a/kernel/bpf/lpm_trie.c
> +++ b/kernel/bpf/lpm_trie.c
> @@ -589,6 +589,7 @@ static void trie_free(struct bpf_map *map)
> 
>  unlock:
>         raw_spin_unlock(&trie->lock);
> +       kfree(trie);
>  }
> 
>  static int trie_get_next_key(struct bpf_map *map, void *_key, void *_next_key)
> -bash-4.2$
> 
> Will propose a formal patch for this soon.

Agree, good catch, and I also think that this is the issue, since this
is what kmemleak reports in terms of size (192):

struct lpm_trie {
        struct bpf_map             map;                  /*     0   128 */
        /* --- cacheline 2 boundary (128 bytes) --- */
        struct lpm_trie_node *     root;                 /*   128     8 */
        size_t                     n_entries;            /*   136     8 */
        size_t                     max_prefixlen;        /*   144     8 */
        size_t                     data_size;            /*   152     8 */
        raw_spinlock_t             lock;                 /*   160     4 */

        /* size: 192, cachelines: 3, members: 6 */
        /* padding: 28 */
};