Re: [PATCH v4 3/20] lsm: Refactor return value of LSM hook inode_getsecurity

Xu Kuohai
2024-07-20T09:28:53Z

On 7/19/2024 10:08 AM, Paul Moore wrote:
> On Jul 11, 2024 Xu Kuohai <xukuohai@huaweicloud.com> wrote:
>>
>> To be consistent with most LSM hooks, convert the return value of
>> hook inode_getsecurity to 0 or a negative error code.
>>
>> Before:
>> - Hook inode_getsecurity returns size of buffer on success or a
>> negative error code on failure.
>>
>> After:
>> - Hook inode_getsecurity returns 0 on success or a negative error
>> code on failure. An output parameter @len is introduced to hold
>> the buffer size on success.
>>
>> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
>> ---
>> fs/xattr.c | 19 ++++++++++---------
>> include/linux/lsm_hook_defs.h | 3 ++-
>> include/linux/security.h | 12 ++++++------
>> security/commoncap.c | 9 ++++++---
>> security/security.c | 11 ++++++-----
>> security/selinux/hooks.c | 16 ++++++----------
>> security/smack/smack_lsm.c | 14 +++++++-------
>> 7 files changed, 43 insertions(+), 41 deletions(-)
>
> Aside from Simon's concern over variable types, I saw a few other issues
> when looking at this patch (below).
>
>> diff --git a/security/commoncap.c b/security/commoncap.c
>> index 17d6188d22cf..ff82e2ab6f8f 100644
>> --- a/security/commoncap.c
>> +++ b/security/commoncap.c
>> @@ -485,7 +485,10 @@ int cap_inode_getsecurity(struct mnt_idmap *idmap,
>> }
>> out_free:
>> kfree(tmpbuf);
>> - return size;
>> + if (size < 0)
>> + return size;
>> + *len = size;
>> + return 0;
>> }
>
> We should do a better job converting cap_inode_getsecurity(), create a
> new local variable, e.g. 'int error', and use it to store and return the
> error code instead of reusing @size. I understand that what you've done
> is easier, but I'd prefer to see it done properly.
>

Got it

>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 9cd5a8f1f6a3..70792bba24d9 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -3407,7 +3407,7 @@ static int selinux_path_notify(const struct path *path, u64 mask,
>> */
>> static int selinux_inode_getsecurity(struct mnt_idmap *idmap,
>> struct inode *inode, const char *name,
>> - void **buffer, bool alloc)
>> + bool alloc, void **buffer, u32 *len)
>> {
>> u32 size;
>> int error;
>> @@ -3440,14 +3440,14 @@ static int selinux_inode_getsecurity(struct mnt_idmap *idmap,
>> &context, &size);
>> if (error)
>> return error;
>> - error = size;
>> + *len = size;
>
> Depending on how you choose to resolve the variable type issue, you may
> be able to pass @len directly to security_sid_to_context().
>

Sounds great

>> if (alloc) {
>> *buffer = context;
>> goto out_nofree;
>> }
>> kfree(context);
>> out_nofree:
>> - return error;
>> + return 0;
>> }
>
>
> --
> paul-moore.com
>
>