[PATCH -next] ima: Handle error code returned by ima_filter_rule_match()

[Roberto Sassu]

On Thu, 2025-11-20 at 15:18 +0800, Zhao Yipeng wrote:
> 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.

Thanks, it makes sense.

Reviewed-by: Roberto Sassu <roberto.sassu at huawei.com>

Roberto

> Fixes: 4af4662fa4a9d ("integrity: IMA policy")
> Signed-off-by: Zhao Yipeng <zhaoyipeng5 at huawei.com>
> ---
>  security/integrity/ima/ima_policy.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 128fab897930..db6d55af5a80 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -674,7 +674,7 @@ static bool ima_match_rules(struct ima_rule_entry *rule,
>  				goto retry;
>  			}
>  		}
> -		if (!rc) {
> +		if (rc <= 0) {
>  			result = false;
>  			goto out;
>  		}