lsm: consolidate buffer size handling into lsm_fill_user_ctx()

While we have a lsm_fill_user_ctx() helper function designed to make
life easier for LSMs which return lsm_ctx structs to userspace, we
didn't include all of the buffer length safety checks and buffer
padding adjustments in the helper.  This led to code duplication
across the different LSMs and the possibility for mistakes across the
different LSM subsystems.  In order to reduce code duplication and
decrease the chances of silly mistakes, we're consolidating all of
this code into the lsm_fill_user_ctx() helper.

The buffer padding is also modified from a fixed 8-byte alignment to
an alignment that matches the word length of the machine
(BITS_PER_LONG / 8).

Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 6 insertions, 17 deletions

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 12160d060cc1..99664c8cf867 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3642,28 +3642,17 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
 static int smack_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
 			     size_t *size, u32 flags)
 {
-	struct smack_known *skp = smk_of_current();
-	int total;
-	int slen;
 	int rc;
+	struct smack_known *skp;
 
 	if (attr != LSM_ATTR_CURRENT)
 		return -EOPNOTSUPP;
 
-	slen = strlen(skp->smk_known) + 1;
-	total = ALIGN(slen + sizeof(*ctx), 8);
-	if (total > *size)
-		rc = -E2BIG;
-	else if (ctx)
-		rc = lsm_fill_user_ctx(ctx, skp->smk_known, slen, LSM_ID_SMACK,
-				       0);
-	else
-		rc = 1;
-
-	*size = total;
-	if (rc >= 0)
-		return 1;
-	return rc;
+	skp = smk_of_current();
+	rc = lsm_fill_user_ctx(ctx, size,
+			       skp->smk_known, strlen(skp->smk_known) + 1,
+			       LSM_ID_SMACK, 0);
+	return (!rc ? 1 : rc);
 }
 
 /**