[PATCH v4 4/20] lsm: Refactor return value of LSM hook inode_listsecurity

Xu Kuohai xukuohai at huaweicloud.com
Sat Jul 20 09:29:10 UTC 2024


On 7/19/2024 10:08 AM, Paul Moore wrote:
> On Jul 11, 2024 Xu Kuohai <xukuohai at huaweicloud.com> wrote:
>>
>> To be consistent with most LSM hooks, convert the return value of
>> hook inode_listsecurity to 0 or a negative error code.
>>
>> Before:
>> - Hook inode_listsecurity returns number of bytes used/required on
>>    success or a negative error code on failure.
>>
>> After:
>> - Hook inode_listsecurity returns 0 on success or a negative error
>>    code on failure. An output parameter @bytes is introduced to hold
>>    the number of bytes used/required on success.
>>
>> Signed-off-by: Xu Kuohai <xukuohai at huawei.com>
>> ---
>>   fs/nfs/nfs4proc.c             |  5 ++++-
>>   fs/xattr.c                    |  5 ++++-
>>   include/linux/lsm_hook_defs.h |  2 +-
>>   include/linux/security.h      |  7 ++++---
>>   net/socket.c                  |  9 +++++----
>>   security/security.c           | 29 +++++++++++++++++++++++++----
>>   security/selinux/hooks.c      |  8 +++++---
>>   security/smack/smack_lsm.c    |  6 ++++--
>>   8 files changed, 52 insertions(+), 19 deletions(-)
>>
>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>> index a691fa10b3e9..6d75758ba3d5 100644
>> --- a/fs/nfs/nfs4proc.c
>> +++ b/fs/nfs/nfs4proc.c
>> @@ -7848,10 +7848,13 @@ static int nfs4_xattr_get_nfs4_label(const struct xattr_handler *handler,
>>   static ssize_t
>>   nfs4_listxattr_nfs4_label(struct inode *inode, char *list, size_t list_len)
>>   {
>> +	size_t bytes;
>>   	int len = 0;
>>   
>>   	if (nfs_server_capable(inode, NFS_CAP_SECURITY_LABEL)) {
>> -		len = security_inode_listsecurity(inode, list, list_len);
>> +		len = security_inode_listsecurity(inode, list, list_len, &bytes);
>> +		if (!len)
>> +			len = bytes;
>>   		if (len >= 0 && list_len && len > list_len)
>>   			return -ERANGE;
>>   	}
> 
> See my comments below.
> 
>> diff --git a/fs/xattr.c b/fs/xattr.c
>> index f4e3bedf7272..ab7d7123a016 100644
>> --- a/fs/xattr.c
>> +++ b/fs/xattr.c
>> @@ -485,6 +485,7 @@ vfs_listxattr(struct dentry *dentry, char *list, size_t size)
>>   {
>>   	struct inode *inode = d_inode(dentry);
>>   	ssize_t error;
>> +	size_t bytes;
>>   
>>   	error = security_inode_listxattr(dentry);
>>   	if (error)
>> @@ -493,7 +494,9 @@ vfs_listxattr(struct dentry *dentry, char *list, size_t size)
>>   	if (inode->i_op->listxattr) {
>>   		error = inode->i_op->listxattr(dentry, list, size);
>>   	} else {
>> -		error = security_inode_listsecurity(inode, list, size);
>> +		error = security_inode_listsecurity(inode, list, size, &bytes);
>> +		if (!error)
>> +			error = bytes;
>>   		if (size && error > size)
>>   			error = -ERANGE;
> 
> More on this below, but since the buffer length is fixed we are
> already going to have to do a length comparison in the LSMs, why not
> do the check and return -ERANGE there?
>

Sounds great, thanks

>> diff --git a/net/socket.c b/net/socket.c
>> index e416920e9399..43f0e3c9a6e0 100644
>> --- a/net/socket.c
>> +++ b/net/socket.c
>> @@ -571,12 +571,13 @@ static struct socket *sockfd_lookup_light(int fd, int *err, int *fput_needed)
>>   static ssize_t sockfs_listxattr(struct dentry *dentry, char *buffer,
>>   				size_t size)
>>   {
>> -	ssize_t len;
>> +	int err;
>> +	size_t len;
>>   	ssize_t used = 0;
>>   
>> -	len = security_inode_listsecurity(d_inode(dentry), buffer, size);
>> -	if (len < 0)
>> -		return len;
>> +	err = security_inode_listsecurity(d_inode(dentry), buffer, size, &len);
>> +	if (err < 0)
>> +		return err;
>>   	used += len;
>>   	if (buffer) {
>>   		if (size < used)
> 
> It doesn't show in the patch/diff, but if the LSM hook handles the length
> comparison we can simplify the -ERANGE code in sockfs_listxattr().
>

Will do

>> diff --git a/security/security.c b/security/security.c
>> index 614f14cbfff7..26eea8f4cd74 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -2597,20 +2597,41 @@ int security_inode_setsecurity(struct inode *inode, const char *name,
>>    * @inode: inode
>>    * @buffer: buffer
>>    * @buffer_size: size of buffer
>> + * @bytes: number of bytes used/required
>>    *
>>    * Copy the extended attribute names for the security labels associated with
>>    * @inode into @buffer.  The maximum size of @buffer is specified by
>>    * @buffer_size.  @buffer may be NULL to request the size of the buffer
>>    * required.
>>    *
>> - * Return: Returns number of bytes used/required on success.
>> + * Return: Returns 0 on success or a negative error code on failure.
>>    */
>>   int security_inode_listsecurity(struct inode *inode,
>> -				char *buffer, size_t buffer_size)
>> +				char *buffer, size_t buffer_size,
>> +				size_t *bytes)
>>   {
>> +	int rc;
>> +	size_t used;
>> +	struct security_hook_list *hp;
>> +
>>   	if (unlikely(IS_PRIVATE(inode)))
>> -		return 0;
>> -	return call_int_hook(inode_listsecurity, inode, buffer, buffer_size);
>> +		return *bytes = 0;
>> +
>> +	used = 0;
>> +	hlist_for_each_entry(hp, &security_hook_heads.inode_listsecurity,
>> +			     list) {
>> +		rc = hp->hook.inode_listsecurity(inode, buffer, buffer_size,
>> +						 &used);
>> +		if (rc < 0)
>> +			return rc;
>> +		if (used != 0)
>> +			break;
>> +	}
>> +
>> +	*bytes = used;
>> +
>> +	return 0;
>> +
>>   }
>>   EXPORT_SYMBOL(security_inode_listsecurity);
> 
> For reasons associated with the static_call work, we really need to
> limit ourselves to the call_{int,void}_hook() macros on any new code.
> The good news is that I think we can do that here as the existing
> code isn't multi-LSM friendly.
>

Thanks for pointing that out. Good to know the current code is acceptable.

>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 70792bba24d9..5dedd3917d57 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -3481,16 +3481,18 @@ static int selinux_inode_setsecurity(struct inode *inode, const char *name,
>>   	return 0;
>>   }
>>   
>> -static int selinux_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size)
>> +static int selinux_inode_listsecurity(struct inode *inode, char *buffer,
>> +				      size_t buffer_size, size_t *bytes)
>>   {
>>   	const int len = sizeof(XATTR_NAME_SELINUX);
>>   
>>   	if (!selinux_initialized())
>> -		return 0;
>> +		return *bytes = 0;
>>   
>>   	if (buffer && len <= buffer_size)
>>   		memcpy(buffer, XATTR_NAME_SELINUX, len);
>> -	return len;
>> +	*bytes = len;
>> +	return 0;
>>   }
> 
> Let's do something like below so we can catch -ERANGE in the LSMs
> themselves.
> 
>    if (!selinux_initialized())
>      return *bytes = 0;
> 
>    *bytes = sizeof(XATTR_NAME_SELINUX);
>    if (len > buffer_size);
>      return -ERANGE;
>    if (buffer)
>      memcpy(buffer, XATTR_NAME_SELINUX, *bytes);
>    
>    return 0;
>

Will do

>>   static void selinux_inode_getsecid(struct inode *inode, u32 *secid)
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index e7a5f6fd9a2d..6f73906bf7ea 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -1611,16 +1611,18 @@ static int smack_inode_getsecurity(struct mnt_idmap *idmap,
>>    * @inode: the object
>>    * @buffer: where they go
>>    * @buffer_size: size of buffer
>> + * @bytes: number of data bytes in buffer
>>    */
>>   static int smack_inode_listsecurity(struct inode *inode, char *buffer,
>> -				    size_t buffer_size)
>> +				    size_t buffer_size, size_t *bytes)
>>   {
>>   	int len = sizeof(XATTR_NAME_SMACK);
>>   
>>   	if (buffer != NULL && len <= buffer_size)
>>   		memcpy(buffer, XATTR_NAME_SMACK, len);
>>   
>> -	return len;
>> +	*bytes = len;
>> +	return 0;
>>   }
> 
> A similar approach could be used here.
>

Will do

> --
> paul-moore.com
> 




More information about the Linux-security-module-archive mailing list