[PATCH 4.19 245/338] mm/mmap: return 1 from stack_guard_gap __setup() handler

Greg Kroah-Hartman
2022-04-14T14:11:11Z

From: Randy Dunlap <rdunlap@infradead.org>

commit e6d094936988910ce6e8197570f2753898830081 upstream.

__setup() handlers should return 1 if the command line option is handled
and 0 if not (or maybe never return 0; it just pollutes init's
environment). This prevents:

Unknown kernel command line parameters \
"BOOT_IMAGE=/boot/bzImage-517rc5 stack_guard_gap=100", will be \
passed to user space.

Run /sbin/init as init process
with arguments:
/sbin/init
with environment:
HOME=/
TERM=linux
BOOT_IMAGE=/boot/bzImage-517rc5
stack_guard_gap=100

Return 1 to indicate that the boot option has been handled.

Note that there is no warning message if someone enters:
stack_guard_gap=anything_invalid
and 'val' and stack_guard_gap are both set to 0 due to the use of
simple_strtoul(). This could be improved by using kstrtoxxx() and
checking for an error.

It appears that having stack_guard_gap == 0 is valid (if unexpected) since
using "stack_guard_gap=0" on the kernel command line does that.

Link: https://lkml.kernel.org/r/20220222005817.11087-1-rdunlap@infradead.org
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
Fixes: 1be7107fbe18e ("mm: larger stack guard gap, between vmas")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Igor Zhbanov <i.zhbanov@omprussia.ru>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/mmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2469,7 +2469,7 @@ static int __init cmdline_parse_stack_gu
if (!*endptr)
stack_guard_gap = val << PAGE_SHIFT;

- return 0;
+ return 1;
}
__setup("stack_guard_gap=", cmdline_parse_stack_guard_gap);