linux-kernel - [PATCH 5.16 0971/1017] mm/mmap: return 1 from stack_guard_gap _

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Date:   Tue,  5 Apr 2022 09:31:24 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Igor Zhbanov <i.zhbanov@...russia.ru>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.16 0971/1017] mm/mmap: return 1 from stack_guard_gap __setup() handler

From: Randy Dunlap <rdunlap@...radead.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@...russia.ru
Fixes: 1be7107fbe18e ("mm: larger stack guard gap, between vmas")
Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
Reported-by: Igor Zhbanov <i.zhbanov@...russia.ru>
Cc: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/mmap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2550,7 +2550,7 @@ 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);