Messages in this thread | | | Date | Tue, 20 Jul 2021 14:51:48 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] prctl: allow to setup brk for et_dyn executables |
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On Fri, 22 Jan 2021 01:12:07 +0300 Cyrill Gorcunov <gorcunov@gmail.com> 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.
So... do you recall why you added that test originally?
This is under prctl(CAP_SET_MM), yes? What capabilities does this require?
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