Re: [PATCH] seccomp: Release fp pointer when leaving from seccomp_attach_filter().

[Alexei Starovoitov]

On Mon, Apr 14, 2014 at 9:02 AM, Masami Ichikawa <masami256@xxxxxxxxx> wrote:
> kmemleak reported some memory leak as below.

grrr. yes. sorry.

> 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
>
> This memory leak happend in seccomp_attach_filter().
> The fp pointer was allocated via kzalloc so that it needs to realase memory
> when leaving from function.
>
> This patch changed two things.
> One is set -ENOMEM to ret, if fp is unable to get memory.
> The other is removes "return 0" statement, and frees fp pointer before
> leaving.
>
> Signed-off-by: Masami Ichikawa <masami256@xxxxxxxxx>
> ---
>  kernel/seccomp.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index d8d046c..a9ce7a9 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -259,8 +259,10 @@ static long seccomp_attach_filter(struct sock_fprog *fprog)
>         filter = kzalloc(sizeof(struct seccomp_filter) +
>                          sizeof(struct sock_filter_int) * new_len,
>                          GFP_KERNEL|__GFP_NOWARN);
> -       if (!filter)
> +       if (!filter) {
> +               ret = -ENOMEM;
>                 goto free_prog;
> +       }

agree. that's a good addition.

>         ret = sk_convert_filter(fp, fprog->len, filter->insnsi, &new_len);
>         if (ret)
> @@ -275,10 +277,10 @@ static long seccomp_attach_filter(struct sock_fprog *fprog)
>          */
>         filter->prev = current->seccomp.filter;
>         current->seccomp.filter = filter;
> -       return 0;

I think mixing error and ok return paths is ugly.
Can you add kfree(fp) here instead of removing return 0?

Thanks!

>  free_filter:
> -       kfree(filter);
> +       if (ret)
> +               kfree(filter);
>  free_prog:
>         kfree(fp);
>         return ret;
> --
> 1.9.1
>
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