ima: Handle error code returned by ima_filter_rule_match()

In ima_match_rules(), if ima_filter_rule_match() returns -ENOENT due to
the rule being NULL, the function incorrectly skips the 'if (!rc)' check
and sets 'result = true'. The LSM rule is considered a match, causing
extra files to be measured by IMA.

This issue can be reproduced in the following scenario:
After unloading the SELinux policy module via 'semodule -d', if an IMA
measurement is triggered before ima_lsm_rules is updated,
in ima_match_rules(), the first call to ima_filter_rule_match() returns
-ESTALE. This causes the code to enter the 'if (rc == -ESTALE &&
!rule_reinitialized)' block, perform ima_lsm_copy_rule() and retry. In
ima_lsm_copy_rule(), since the SELinux module has been removed, the rule
becomes NULL, and the second call to ima_filter_rule_match() returns
-ENOENT. This bypasses the 'if (!rc)' check and results in a false match.

Call trace:
  selinux_audit_rule_match+0x310/0x3b8
  security_audit_rule_match+0x60/0xa0
  ima_match_rules+0x2e4/0x4a0
  ima_match_policy+0x9c/0x1e8
  ima_get_action+0x48/0x60
  process_measurement+0xf8/0xa98
  ima_bprm_check+0x98/0xd8
  security_bprm_check+0x5c/0x78
  search_binary_handler+0x6c/0x318
  exec_binprm+0x58/0x1b8
  bprm_execve+0xb8/0x130
  do_execveat_common.isra.0+0x1a8/0x258
  __arm64_sys_execve+0x48/0x68
  invoke_syscall+0x50/0x128
  el0_svc_common.constprop.0+0xc8/0xf0
  do_el0_svc+0x24/0x38
  el0_svc+0x44/0x200
  el0t_64_sync_handler+0x100/0x130
  el0t_64_sync+0x3c8/0x3d0

Fix this by changing 'if (!rc)' to 'if (rc <= 0)' to ensure that error
codes like -ENOENT do not bypass the check and accidentally result in a
successful match.

Fixes: 4af4662fa4 ("integrity: IMA policy")
Signed-off-by: Zhao Yipeng <zhaoyipeng5@huawei.com>
Reviewed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/ima/ima_policy.c

@@ -685,7 +685,7 @@ static bool ima_match_rules(struct ima_rule_entry *rule,
 				goto retry;
 			}
 		}
-		if (!rc) {
+		if (rc <= 0) {
 			result = false;
 			goto out;
 		}