[PATCH 5.15 210/913] EVM: fix the evm= __setup handler return value

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 11:20:55 EST

From: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>

[ Upstream commit f2544f5e6c691679d56bb38637d2f347075b36fa ]

__setup() handlers should return 1 if the parameter is handled.
Returning 0 causes the entire string to be added to init's
environment strings (limited to 32 strings), unnecessarily polluting it.

Using the documented string "evm=fix" causes an Unknown parameter message:
Unknown kernel command line parameters
"BOOT_IMAGE=/boot/bzImage-517rc5 evm=fix", will be passed to user space.

and that string is added to init's environment string space:
Run /sbin/init as init process
with arguments:
with environment:

With this change, using "evm=fix" acts as expected and an invalid
option ("evm=evm") causes a warning to be printed:
evm: invalid "evm" mode
but init's environment is not polluted with this string, as expected.

Fixes: 7102ebcd65c1 ("evm: permit only valid security.evm xattrs to be updated")
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Reported-by: Igor Zhbanov <i.zhbanov@xxxxxxxxxxxx>
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@xxxxxxxxxxxx
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
security/integrity/evm/evm_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 08f907382c61..7d87772f0ce6 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -86,7 +86,7 @@ static int __init evm_set_fixmode(char *str)
pr_err("invalid \"%s\" mode", str);

- return 0;
+ return 1;
__setup("evm=", evm_set_fixmode);