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

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On 7/19/2024 10:08 AM, Paul Moore wrote:
On Jul 11, 2024 Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> 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@xxxxxxxxxx>
---
  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







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