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    Subject[PATCH v4 14/15] exec: Use sane stack rlimit under secureexec
    Date
    For a secureexec, before memory layout selection has happened, reset the
    stack rlimit to something sane to avoid the caller having control over
    the resulting layouts.

    $ ulimit -s
    8192
    $ ulimit -s unlimited
    $ /bin/sh -c 'ulimit -s'
    unlimited
    $ sudo /bin/sh -c 'ulimit -s'
    8192

    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    Reviewed-by: James Morris <james.l.morris@oracle.com>
    Acked-by: Serge Hallyn <serge@hallyn.com>
    ---
    fs/exec.c | 12 ++++++++++++
    1 file changed, 12 insertions(+)

    diff --git a/fs/exec.c b/fs/exec.c
    index 3ae8a40c587b..cddd2a2cbc1f 100644
    --- a/fs/exec.c
    +++ b/fs/exec.c
    @@ -1329,6 +1329,18 @@ void setup_new_exec(struct linux_binprm * bprm)
    */
    bprm->secureexec |= bprm->cap_elevated;

    + if (bprm->secureexec) {
    + /*
    + * For secureexec, reset the stack limit to sane default to
    + * avoid bad behavior from the prior rlimits. This has to
    + * happen before arch_pick_mmap_layout(), which examines
    + * RLIMIT_STACK, but after the point of no return to avoid
    + * needing to clean up the change on failure.
    + */
    + if (current->signal->rlim[RLIMIT_STACK].rlim_cur > _STK_LIM)
    + current->signal->rlim[RLIMIT_STACK].rlim_cur = _STK_LIM;
    + }
    +
    arch_pick_mmap_layout(current->mm);

    current->sas_ss_sp = current->sas_ss_size = 0;
    --
    2.7.4
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