• Helge Deller's avatar
    parisc,metag: Fix crashes due to stack randomization on stack-grows-upwards architectures · d045c77c
    Helge Deller authored
    On architectures where the stack grows upwards (CONFIG_STACK_GROWSUP=y,
    currently parisc and metag only) stack randomization sometimes leads to crashes
    when the stack ulimit is set to lower values than STACK_RND_MASK (which is 8 MB
    by default if not defined in arch-specific headers).
    
    The problem is, that when the stack vm_area_struct is set up in fs/exec.c, the
    additional space needed for the stack randomization (as defined by the value of
    STACK_RND_MASK) was not taken into account yet and as such, when the stack
    randomization code added a random offset to the stack start, the stack
    effectively got smaller than what the user defined via rlimit_max(RLIMIT_STACK)
    which then sometimes leads to out-of-stack situations and crashes.
    
    This patch fixes it by adding the maximum possible amount of memory (based on
    STACK_RND_MASK) which theoretically could be added by the stack randomization
    code to the initial stack size. That way, the user-defined stack size is always
    guaranteed to be at minimum what is defined via rlimit_max(RLIMIT_STACK).
    
    This bug is currently not visible on the metag architecture, because on metag
    STACK_RND_MASK is defined to 0 which effectively disables stack randomization.
    
    The changes to fs/exec.c are inside an "#ifdef CONFIG_STACK_GROWSUP"
    section, so it does not affect other platformws beside those where the
    stack grows upwards (parisc and metag).
    Signed-off-by: default avatarHelge Deller <deller@gmx.de>
    Cc: linux-parisc@vger.kernel.org
    Cc: James Hogan <james.hogan@imgtec.com>
    Cc: linux-metag@vger.kernel.org
    Cc: stable@vger.kernel.org # v3.16+
    d045c77c
exec.c 40.6 KB