This is a note to let you know that I've just added the patch titled
exec: Limit arg stack to at most 75% of _STK_LIM
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
exec-limit-arg-stack-to-at-most-75-of-_stk_lim.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From da029c11e6b12f321f36dac8771e833b65cec962 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@xxxxxxxxxxxx>
Date: Fri, 7 Jul 2017 11:57:29 -0700
Subject: exec: Limit arg stack to at most 75% of _STK_LIM
From: Kees Cook <keescook@xxxxxxxxxxxx>
commit da029c11e6b12f321f36dac8771e833b65cec962 upstream.
To avoid pathological stack usage or the need to special-case setuid
execs, just limit all arg stack usage to at most 75% of _STK_LIM (6MB).
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -206,8 +206,7 @@ static struct page *get_arg_page(struct
if (write) {
unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
- unsigned long ptr_size;
- struct rlimit *rlim;
+ unsigned long ptr_size, limit;
/*
* Since the stack will hold pointers to the strings, we
@@ -236,14 +235,16 @@ static struct page *get_arg_page(struct
return page;
/*
- * Limit to 1/4-th the stack size for the argv+env strings.
+ * Limit to 1/4 of the max stack size or 3/4 of _STK_LIM
+ * (whichever is smaller) for the argv+env strings.
* This ensures that:
* - the remaining binfmt code will not run out of stack space,
* - the program will have a reasonable amount of stack left
* to work from.
*/
- rlim = current->signal->rlim;
- if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4)
+ limit = _STK_LIM / 4 * 3;
+ limit = min(limit, rlimit(RLIMIT_STACK) / 4);
+ if (size > limit)
goto fail;
}
Patches currently in stable-queue which might be from keescook@xxxxxxxxxxxx are
queue-4.4/binfmt_elf-use-elf_et_dyn_base-only-for-pie.patch
queue-4.4/exec-limit-arg-stack-to-at-most-75-of-_stk_lim.patch
queue-4.4/s390-reduce-elf_et_dyn_base.patch
queue-4.4/arm-move-elf_et_dyn_base-to-4mb.patch
queue-4.4/arm64-move-elf_et_dyn_base-to-4gb-4mb.patch
queue-4.4/selftests-capabilities-fix-the-test_execve-test.patch
queue-4.4/powerpc-move-elf_et_dyn_base-to-4gb-4mb.patch