4.12-stable review patch. If anyone has any objections, please let me know.
------------------
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
@@ -220,8 +220,7 @@ 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
@@ -250,14 +249,16 @@ 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;
}