[PATCH 4.4 33/57] exec: Limit arg stack to at most 75% of _STK_LIM

Greg Kroah-Hartman
2017-07-19T11:14:14Z

From: Kees Cook <keescook@chromium.org>

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@chromium.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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;
}