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authorHelge Deller <deller@gmx.de>2015-05-11 22:01:27 +0200
committerHelge Deller <deller@gmx.de>2015-05-12 22:03:44 +0200
commitd045c77c1a69703143a36169c224429c48b9eecd (patch)
treef71e78b7585011274db82483cd95718e11171277 /drivers
parent5fec97d0e3d93717f1d6a958a03e579078088861 (diff)
downloadlwn-d045c77c1a69703143a36169c224429c48b9eecd.tar.gz
lwn-d045c77c1a69703143a36169c224429c48b9eecd.zip
parisc,metag: Fix crashes due to stack randomization on stack-grows-upwards architectures
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: Helge 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+
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