[PATCH] EVM: fix the evm= __setup handler return value

[Randy Dunlap <rdunlap@xxxxxxxxxxxxx>]

__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:
     /sbin/init
    with environment:
     HOME=/
     TERM=linux
     BOOT_IMAGE=/boot/bzImage-517rc5
     evm=fix

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
Cc: Mimi Zohar <zohar@xxxxxxxxxx>
Cc: linux-integrity@xxxxxxxxxxxxxxx
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
---
 security/integrity/evm/evm_main.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- lnx-517-rc5.orig/security/integrity/evm/evm_main.c
+++ lnx-517-rc5/security/integrity/evm/evm_main.c
@@ -86,7 +86,7 @@ static int __init evm_set_fixmode(char *
 	else
 		pr_err("invalid \"%s\" mode", str);
 
-	return 0;
+	return 1;
 }
 __setup("evm=", evm_set_fixmode);