[PATCH v2 1/2] ima_setup.sh: Fix check_policy_writable() for kernel < 4.5

[Petr Vorel <pvorel@suse.cz>]

Writing into policy via echo on kernel < 4.5 effectively makes policy
not writable (no point to check if the policy is writable). Therefore
skip this extra check in check_policy_writable() on these old kernels.

This change improves IMA testing on kernel < 4.5:

1) Allows to run ima_policy.sh which was previously skipped:

    ima_policy 1 TINFO: verify that invalid policy isn't loaded
    ima_policy 1 TCONF: IMA policy already loaded and kernel not configured to enable multiple writes to it (need CONFIG_IMA_WRITE_POLICY=y)

2) Fixes failing ima_violations.sh, which was failing due policy was not
   writable:

    ima_violations 1 TINFO: Tested kernel: Linux susetest 4.4.140
    ima_violations 1 TINFO: booted with IMA policy: tcb
    ima_violations 1 TINFO: using log /var/log/audit/audit.log
    ima_violations 1 TINFO: verify open writers violation
    ima_violations 1 TFAIL: open_writers violation not added
    ima_violations 2 TINFO: verify ToMToU violation
    ima_violations 2 TFAIL: ToMToU violation not added
    ima_violations 3 TINFO: verify open_writers using mmapped files
    tst_kconfig.c:90: TINFO: Parsing kernel config '/proc/config.gz'
    tst_kconfig.c:90: TINFO: Parsing kernel config '/proc/config.gz'
    tst_kconfig.c:755: TINFO: CONFIG_FAULT_INJECTION kernel option detected which might slow the execution
    tst_kconfig.c:755: TINFO: CONFIG_FAULT_INJECTION kernel option detected which might slow the execution
    tst_kconfig.c:90: TINFO: Parsing kernel config '/proc/config.gz'
    tst_kconfig.c:755: TINFO: CONFIG_FAULT_INJECTION kernel option detected which might slow the execution
    ima_mmap.c:33: TPASS: test completed
    ima_violations 3 TFAIL: open_writers violation not added

3) Fixes failing ima_conditionals.sh -r uid and ima_conditionals.sh -r fowner

    ima_conditionals 1 TINFO: request 'uid'
    tst_security.c:115: TINFO: SecureBoot sysfs file not available
    ima_conditionals 1 TINFO: verify measuring user files when requested via uid
    tst_rod: Failed to open '/sys/kernel/security/ima/policy' for writing: Permission denied
    ima_conditionals 1 TBROK: echo measure uid=65534 > /sys/kernel/security/ima/policy failed

    ima_conditionals 1 TINFO: request 'fowner'
    tst_security.c:115: TINFO: SecureBoot sysfs file not available
    ima_conditionals 1 TINFO: verify measuring user files when requested via fowner
    tst_rod: Failed to open '/sys/kernel/security/ima/policy' for writing: Permission denied
    ima_conditionals 1 TBROK: echo measure fowner=65534 > /sys/kernel/security/ima/policy failed

Fixes: cd96265e65 ("ima/ima_policy.sh: Improve check of policy writability")
Signed-off-by: Petr Vorel <pvorel@suse.cz>
---
The same in v1.

@Mimi I appreciate your RBT or ABT.

Link to v1:
https://lore.kernel.org/ltp/20260728114224.1055009-1-pvorel@suse.cz/T/#t

 .../kernel/security/integrity/ima/tests/ima_setup.sh  | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/testcases/kernel/security/integrity/ima/tests/ima_setup.sh b/testcases/kernel/security/integrity/ima/tests/ima_setup.sh
index b69d7c31d9..19f00532b1 100644
--- a/testcases/kernel/security/integrity/ima/tests/ima_setup.sh
+++ b/testcases/kernel/security/integrity/ima/tests/ima_setup.sh
@@ -95,10 +95,15 @@ require_policy_readable()
 check_policy_writable()
 {
 	[ -f $IMA_POLICY ] || return 1
-	# workaround for kernels < v4.18 without fix
+
+	# Workaround for kernels < v4.18 without fix
 	# ffb122de9a60b ("ima: Reflect correct permissions for policy")
-	echo "" 2> log > $IMA_POLICY
-	grep -q "Device or resource busy" log && return 1
+	# Require >= 4.5 to write multiple times via CONFIG_IMA_WRITE_POLICY
+	# 38d859f991f3 ("IMA: policy can now be updated multiple times")
+	if tst_kvcmp -ge 4.5; then
+		echo "" 2> log > $IMA_POLICY
+		grep -q "Device or resource busy" log && return 1
+	fi
 	return 0
 }
 
-- 
2.55.0