From: Cyrill Gorcunov <gorcunov@xxxxxxxxx> Subject: prctl: allow to setup brk for et_dyn executables 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. Link: https://lkml.kernel.org/r/20210121221207.GB2174@grain Fixes: bbdc6076d2e5 ("binfmt_elf: move brk out of mmap when doing direct loader exec") Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxx> Reported-by: Keno Fischer <keno@xxxxxxxxxxxxxxxxxx> Acked-by: Andrey Vagin <avagin@xxxxxxxxx> Tested-by: Andrey Vagin <avagin@xxxxxxxxx> Cc: Dmitry Safonov <0x7f454c46@xxxxxxxxx> Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> Cc: Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx> Cc: Alexander Mikhalitsyn <alexander.mikhalitsyn@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/sys.c | 7 ------- 1 file changed, 7 deletions(-) --- a/kernel/sys.c~prctl-allow-to-setup-brk-for-et_dyn-executables +++ a/kernel/sys.c @@ -1960,13 +1960,6 @@ 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, _
