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Commit da029c11 authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds
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exec: Limit arg stack to at most 75% of _STK_LIM 



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: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 088737f4

fs/exec.c

+6 −5
Original line number Diff line number Diff line
@@ -220,8 +220,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, 


	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
@@ -250,14 +249,16 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, 
			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;

	}