Re: [PATCH] seccomp: fix memory leak on filter attach

[Kees Cook]

On Mon, Apr 14, 2014 at 10:17 AM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
> On Mon, Apr 14, 2014 at 10:11 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> This sets the correct error code when final filter memory is unavailable,
>> and frees the raw filter no matter what.
>>
>> unreferenced object 0xffff8800d6ea4000 (size 512):
>>   comm "sshd", pid 278, jiffies 4294898315 (age 46.653s)
>>   hex dump (first 32 bytes):
>>     21 00 00 00 04 00 00 00 15 00 01 00 3e 00 00 c0  !...........>...
>>     06 00 00 00 00 00 00 00 21 00 00 00 00 00 00 00  ........!.......
>>   backtrace:
>>     [<ffffffff8151414e>] kmemleak_alloc+0x4e/0xb0
>>     [<ffffffff811a3a40>] __kmalloc+0x280/0x320
>>     [<ffffffff8110842e>] prctl_set_seccomp+0x11e/0x3b0
>>     [<ffffffff8107bb6b>] SyS_prctl+0x3bb/0x4a0
>>     [<ffffffff8152ef2d>] system_call_fastpath+0x1a/0x1f
>>     [<ffffffffffffffff>] 0xffffffffffffffff
>>
>> Reported-by: Masami Ichikawa <masami256@xxxxxxxxx>
>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx
>
> Acked-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
>
>> ---
>>  kernel/seccomp.c |    2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
>> index fd609bd9d6dd..2d7dcdfb7422 100644
>> --- a/kernel/seccomp.c
>> +++ b/kernel/seccomp.c
>> @@ -256,6 +256,7 @@ static long seccomp_attach_filter(struct sock_fprog *fprog)
>>                 goto free_prog;
>>
>>         /* Allocate a new seccomp_filter */
>> +       ret = -ENOMEM;
>>         filter = kzalloc(sizeof(struct seccomp_filter) +
>>                          sizeof(struct sock_filter_int) * new_len,
>>                          GFP_KERNEL|__GFP_NOWARN);
>> @@ -265,6 +266,7 @@ static long seccomp_attach_filter(struct sock_fprog *fprog)
>>         ret = sk_convert_filter(fp, fprog->len, filter->insnsi, &new_len);
>>         if (ret)
>>                 goto free_filter;
>> +       kfree(fp);
>>
>>         atomic_set(&filter->usage, 1);
>>         filter->len = new_len;
>> --
>> 1.7.9.5
>>
>>
>> --
>> Kees Cook
>> Chrome OS Security

James (or anyone), can you be sure to pull this soon? I'd like to get
it into 3.14 stable ASAP. Under kernel memory pressure, it would be
possible for the prctl to return 0 without having attached the seccomp
filter.

Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security
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