[PATCH 5.10 579/599] mm/usercopy: return 1 from hardened_usercopy __setup() handler

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 21:00:15 EST

From: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>

commit 05fe3c103f7e6b8b4fca8a7001dfc9ed4628085b 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 hardened_usercopy=off", will be \
passed to user space.

Run /sbin/init as init process
with arguments:
with environment:
but when "hardened_usercopy=foo" is used, there is no Unknown kernel
command line parameter.

Return 1 to indicate that the boot option has been handled.
Print a warning if strtobool() returns an error on the option string,
but do not mark this as in unknown command line option and do not cause
init's environment to be polluted with this string.

Link: https://lkml.kernel.org/r/20220222034249.14795-1-rdunlap@xxxxxxxxxxxxx
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@xxxxxxxxxxxx
Fixes: b5cb15d9372ab ("usercopy: Allow boot cmdline disabling of hardening")
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Reported-by: Igor Zhbanov <i.zhbanov@xxxxxxxxxxxx>
Acked-by: Chris von Recklinghausen <crecklin@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
mm/usercopy.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -294,7 +294,10 @@ static bool enable_checks __initdata = t

static int __init parse_hardened_usercopy(char *str)
- return strtobool(str, &enable_checks);
+ if (strtobool(str, &enable_checks))
+ pr_warn("Invalid option string for hardened_usercopy: '%s'\n",
+ str);
+ return 1;

__setup("hardened_usercopy=", parse_hardened_usercopy);