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exec: Limit arg stack to at most 75% of _STK_LIM

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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>
This commit is contained in:
Kees Cook 2017-07-07 11:57:29 -07:00 committed by Linus Torvalds
parent 088737f44b
commit da029c11e6
1 changed files with 6 additions and 5 deletions
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11
fs/exec.c
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@ -220,8 +220,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
if (write) { if (write) {
unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
unsigned long ptr_size; unsigned long ptr_size, limit;
struct rlimit *rlim;
/* /*
* Since the stack will hold pointers to the strings, we * 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; 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: * This ensures that:
* - the remaining binfmt code will not run out of stack space, * - the remaining binfmt code will not run out of stack space,
* - the program will have a reasonable amount of stack left * - the program will have a reasonable amount of stack left
* to work from. * to work from.
*/ */
rlim = current->signal->rlim; limit = _STK_LIM / 4 * 3;
if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) limit = min(limit, rlimit(RLIMIT_STACK) / 4);
if (size > limit)
goto fail; goto fail;
} }