[PATCH 4.9 047/128] Smack: slab-out-of-bounds in vsscanf

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>

commit 84e99e58e8d1e26f04c097f4266e431a33987f36 upstream.

Add barrier to soob. Return -EOVERFLOW if the buffer
is exceeded.

Suggested-by: Hillf Danton <hdanton@xxxxxxxx>
Reported-by: syzbot+bfdd4a2f07be52351350@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 security/smack/smackfs.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -901,11 +901,21 @@ static ssize_t smk_set_cipso(struct file
 	else
 		rule += strlen(skp->smk_known) + 1;
 
+	if (rule > data + count) {
+		rc = -EOVERFLOW;
+		goto out;
+	}
+
 	ret = sscanf(rule, "%d", &maplevel);
 	if (ret != 1 || maplevel > SMACK_CIPSO_MAXLEVEL)
 		goto out;
 
 	rule += SMK_DIGITLEN;
+	if (rule > data + count) {
+		rc = -EOVERFLOW;
+		goto out;
+	}
+
 	ret = sscanf(rule, "%d", &catlen);
 	if (ret != 1 || catlen > SMACK_CIPSO_MAXCATNUM)
 		goto out;