CC: Pavel and Alexander
On 22.01.2021 01:12, Cyrill Gorcunov wrote:
> Keno Fischer reported that when a binray loaded via
> ld-linux-x the prctl(PR_SET_MM_MAP) doesn't allow to
> setup brk value because it lays before mm:end_data.
>
> For example a test program shows
>
> | # ~/t
> |
> | start_code 401000
> | end_code 401a15
> | start_stack 7ffce4577dd0
> | start_data 403e10
> | end_data 40408c
> | start_brk b5b000
> | sbrk(0) b5b000
>
> and when executed via ld-linux
>
> | # /lib64/ld-linux-x86-64.so.2 ~/t
> |
> | start_code 7fc25b0a4000
> | end_code 7fc25b0c4524
> | start_stack 7fffcc6b2400
> | start_data 7fc25b0ce4c0
> | end_data 7fc25b0cff98
> | start_brk 55555710c000
> | sbrk(0) 55555710c000
>
> This of course prevent criu from restoring such programs.
> Looking into how kernel operates with brk/start_brk inside
> brk() syscall I don't see any problem if we allow to setup
> brk/start_brk without checking for end_data. Even if someone
> pass some weird address here on a purpose then the worst
> possible result will be an unexpected unmapping of existing
> vma (own vma, since prctl works with the callers memory) but
> test for RLIMIT_DATA is still valid and a user won't be able
> to gain more memory in case of expanding VMAs via new values
> shipped with prctl call.
>
> Reported-by: Keno Fischer <k...@juliacomputing.com>
> Signed-off-by: Cyrill Gorcunov <gorcu...@gmail.com>
> CC: Andrew Morton <a...@linux-foundation.org>
> CC: Dmitry Safonov <0x7f454...@gmail.com>
> CC: Andrey Vagin <ava...@gmail.com>
> CC: Kirill Tkhai <ktk...@virtuozzo.com>
> CC: Eric W. Biederman <ebied...@xmission.com>
> ---
> Guys, take a look please once time permit. Hopefully I didn't
> miss something 'cause made this patch via code reading only.
>
> Andrey, do we still have a criu container which tests new kernels,
> right? Would be great to run criu tests with this patch applied
> to make sure everything is intact.
>
> kernel/sys.c | 7 -------
> 1 file changed, 7 deletions(-)
>
> Index: linux-tip.git/kernel/sys.c
> ===================================================================
> --- linux-tip.git.orig/kernel/sys.c
> +++ linux-tip.git/kernel/sys.c
> @@ -1943,13 +1943,6 @@ static int validate_prctl_map_addr(struc
> error = -EINVAL;
>
> /*
> - * @brk should be after @end_data in traditional maps.
> - */
> - if (prctl_map->start_brk <= prctl_map->end_data ||
> - prctl_map->brk <= prctl_map->end_data)
> - goto out;
> -
> - /*
> * Neither we should allow to override limits if they set.
> */
> if (check_data_rlimit(rlimit(RLIMIT_DATA), prctl_map->brk,
>
