[bpf-next,v4,05/20] lsm: Refactor return value of LSM hook inode_copy_up_xattr

Commit Message

Xu Kuohai July 11, 2024, 11:18 a.m. UTC

From: Xu Kuohai <[e-mail]>

To be consistent with most LSM hooks, convert the return value of
hook inode_copy_up_xattr to 0 or a negative error code.

Before:
- Hook inode_copy_up_xattr returns 0 when accepting xattr, 1 when
  discarding xattr, -EOPNOTSUPP if it does not know xattr, or any
  other negative error code otherwise.

After:
- Hook inode_copy_up_xattr returns 0 when accepting xattr, *-ECANCELED*
  when discarding xattr, -EOPNOTSUPP if it does not know xattr, or
  any other negative error code otherwise.

Signed-off-by: Xu Kuohai <[e-mail]>
---
 fs/overlayfs/copy_up.c            |  6 +++---
 security/integrity/evm/evm_main.c |  2 +-
 security/security.c               | 12 ++++++------
 security/selinux/hooks.c          |  4 ++--
 security/smack/smack_lsm.c        |  6 +++---
 5 files changed, 15 insertions(+), 15 deletions(-)

Comments

Paul Moore July 19, 2024, 2:08 a.m. UTC | #1

On Jul 11, 2024 Xu Kuohai <[e-mail]> wrote:
> 
> To be consistent with most LSM hooks, convert the return value of
> hook inode_copy_up_xattr to 0 or a negative error code.
> 
> Before:
> - Hook inode_copy_up_xattr returns 0 when accepting xattr, 1 when
>   discarding xattr, -EOPNOTSUPP if it does not know xattr, or any
>   other negative error code otherwise.
> 
> After:
> - Hook inode_copy_up_xattr returns 0 when accepting xattr, *-ECANCELED*
>   when discarding xattr, -EOPNOTSUPP if it does not know xattr, or
>   any other negative error code otherwise.
> 
> Signed-off-by: Xu Kuohai <[e-mail]>
> ---
>  fs/overlayfs/copy_up.c            |  6 +++---
>  security/integrity/evm/evm_main.c |  2 +-
>  security/security.c               | 12 ++++++------
>  security/selinux/hooks.c          |  4 ++--
>  security/smack/smack_lsm.c        |  6 +++---
>  5 files changed, 15 insertions(+), 15 deletions(-)

...

> diff --git a/security/security.c b/security/security.c
> index 26eea8f4cd74..12215ca286af 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2675,18 +2675,18 @@ EXPORT_SYMBOL(security_inode_copy_up);
>   * lower layer to the union/overlay layer.   The caller is responsible for
>   * reading and writing the xattrs, this hook is merely a filter.
>   *
> - * Return: Returns 0 to accept the xattr, 1 to discard the xattr, -EOPNOTSUPP
> - *         if the security module does not know about attribute, or a negative
> - *         error code to abort the copy up.
> + * Return: Returns 0 to accept the xattr, -ECANCELED to discard the xattr,
> + *         -EOPNOTSUPP if the security module does not know about attribute,
> + *         or a negative error code to abort the copy up.
>   */
>  int security_inode_copy_up_xattr(struct dentry *src, const char *name)
>  {
>  	int rc;
>  
>  	/*
> -	 * The implementation can return 0 (accept the xattr), 1 (discard the
> -	 * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
> -	 * any other error code in case of an error.
> +	 * The implementation can return 0 (accept the xattr), -ECANCELED
> +	 * (discard the xattr), -EOPNOTSUPP if it does not know anything
> +	 *  about the xattr or any other error code in case of an error.
>  	 */

Updating the comment here is good, but considering that we also discuss
the return value in the function header comment, I think it might be
better to just remove this comment entirely and leave the function header
comment as the single source.  Duplicated comments/docs tend to fall out
of sync and create confusion.

>  	rc = call_int_hook(inode_copy_up_xattr, src, name);
>  	if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))


--
paul-moore.com

Xu Kuohai July 20, 2024, 9:29 a.m. UTC | #2

On 7/19/2024 10:08 AM, Paul Moore wrote:
> On Jul 11, 2024 Xu Kuohai <[e-mail]> wrote:
>>
>> To be consistent with most LSM hooks, convert the return value of
>> hook inode_copy_up_xattr to 0 or a negative error code.
>>
>> Before:
>> - Hook inode_copy_up_xattr returns 0 when accepting xattr, 1 when
>>    discarding xattr, -EOPNOTSUPP if it does not know xattr, or any
>>    other negative error code otherwise.
>>
>> After:
>> - Hook inode_copy_up_xattr returns 0 when accepting xattr, *-ECANCELED*
>>    when discarding xattr, -EOPNOTSUPP if it does not know xattr, or
>>    any other negative error code otherwise.
>>
>> Signed-off-by: Xu Kuohai <[e-mail]>
>> ---
>>   fs/overlayfs/copy_up.c            |  6 +++---
>>   security/integrity/evm/evm_main.c |  2 +-
>>   security/security.c               | 12 ++++++------
>>   security/selinux/hooks.c          |  4 ++--
>>   security/smack/smack_lsm.c        |  6 +++---
>>   5 files changed, 15 insertions(+), 15 deletions(-)
> 
> ...
> 
>> diff --git a/security/security.c b/security/security.c
>> index 26eea8f4cd74..12215ca286af 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -2675,18 +2675,18 @@ EXPORT_SYMBOL(security_inode_copy_up);
>>    * lower layer to the union/overlay layer.   The caller is responsible for
>>    * reading and writing the xattrs, this hook is merely a filter.
>>    *
>> - * Return: Returns 0 to accept the xattr, 1 to discard the xattr, -EOPNOTSUPP
>> - *         if the security module does not know about attribute, or a negative
>> - *         error code to abort the copy up.
>> + * Return: Returns 0 to accept the xattr, -ECANCELED to discard the xattr,
>> + *         -EOPNOTSUPP if the security module does not know about attribute,
>> + *         or a negative error code to abort the copy up.
>>    */
>>   int security_inode_copy_up_xattr(struct dentry *src, const char *name)
>>   {
>>   	int rc;
>>   
>>   	/*
>> -	 * The implementation can return 0 (accept the xattr), 1 (discard the
>> -	 * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
>> -	 * any other error code in case of an error.
>> +	 * The implementation can return 0 (accept the xattr), -ECANCELED
>> +	 * (discard the xattr), -EOPNOTSUPP if it does not know anything
>> +	 *  about the xattr or any other error code in case of an error.
>>   	 */
> 
> Updating the comment here is good, but considering that we also discuss
> the return value in the function header comment, I think it might be
> better to just remove this comment entirely and leave the function header
> comment as the single source.  Duplicated comments/docs tend to fall out
> of sync and create confusion.
>

OK, will do

>>   	rc = call_int_hook(inode_copy_up_xattr, src, name);
>>   	if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
> 
> 
> --
> paul-moore.com
>

Patch

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index a5ef2005a2cc..337a5be99ac9 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -115,12 +115,12 @@  int ovl_copy_xattr(struct super_block *sb, const struct path *oldpath, struct de
 			continue;
 
 		error = security_inode_copy_up_xattr(old, name);
-		if (error < 0 && error != -EOPNOTSUPP)
-			break;
-		if (error == 1) {
+		if (error == -ECANCELED) {
 			error = 0;
 			continue; /* Discard */
 		}
+		if (error < 0 && error != -EOPNOTSUPP)
+			break;
 
 		if (is_posix_acl_xattr(name)) {
 			error = ovl_copy_acl(OVL_FS(sb), oldpath, new, name);
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 62fe66dd53ce..6924ed508ebd 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -1000,7 +1000,7 @@  static int evm_inode_copy_up_xattr(struct dentry *src, const char *name)
 	case EVM_XATTR_HMAC:
 	case EVM_IMA_XATTR_DIGSIG:
 	default:
-		rc = 1; /* discard */
+		rc = -ECANCELED; /* discard */
 	}
 
 	kfree(xattr_data);
diff --git a/security/security.c b/security/security.c
index 26eea8f4cd74..12215ca286af 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2675,18 +2675,18 @@  EXPORT_SYMBOL(security_inode_copy_up);
  * lower layer to the union/overlay layer.   The caller is responsible for
  * reading and writing the xattrs, this hook is merely a filter.
  *
- * Return: Returns 0 to accept the xattr, 1 to discard the xattr, -EOPNOTSUPP
- *         if the security module does not know about attribute, or a negative
- *         error code to abort the copy up.
+ * Return: Returns 0 to accept the xattr, -ECANCELED to discard the xattr,
+ *         -EOPNOTSUPP if the security module does not know about attribute,
+ *         or a negative error code to abort the copy up.
  */
 int security_inode_copy_up_xattr(struct dentry *src, const char *name)
 {
 	int rc;
 
 	/*
-	 * The implementation can return 0 (accept the xattr), 1 (discard the
-	 * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
-	 * any other error code in case of an error.
+	 * The implementation can return 0 (accept the xattr), -ECANCELED
+	 * (discard the xattr), -EOPNOTSUPP if it does not know anything
+	 *  about the xattr or any other error code in case of an error.
 	 */
 	rc = call_int_hook(inode_copy_up_xattr, src, name);
 	if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 5dedd3917d57..f9a6637dfd78 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3528,8 +3528,8 @@  static int selinux_inode_copy_up_xattr(struct dentry *dentry, const char *name)
 	 * xattrs up.  Instead, filter out SELinux-related xattrs following
 	 * policy load.
 	 */
-	if (selinux_initialized() && strcmp(name, XATTR_NAME_SELINUX) == 0)
-		return 1; /* Discard */
+	if (selinux_initialized() && !strcmp(name, XATTR_NAME_SELINUX))
+		return -ECANCELED; /* Discard */
 	/*
 	 * Any other attribute apart from SELINUX is not claimed, supported
 	 * by selinux.
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 6f73906bf7ea..ae8f1c2d0ca6 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4893,10 +4893,10 @@  static int smack_inode_copy_up(struct dentry *dentry, struct cred **new)
 static int smack_inode_copy_up_xattr(struct dentry *src, const char *name)
 {
 	/*
-	 * Return 1 if this is the smack access Smack attribute.
+	 * Return -ECANCELED if this is the smack access Smack attribute.
 	 */
-	if (strcmp(name, XATTR_NAME_SMACK) == 0)
-		return 1;
+	if (!strcmp(name, XATTR_NAME_SMACK))
+		return -ECANCELED;
 
 	return -EOPNOTSUPP;
 }