smackfs: Prevent underflow in smk_set_cipso()

There is a upper bound to "catlen" but no lower bound to prevent
negatives.  I don't see that this necessarily causes a problem but we
may as well be safe.

Fixes: e114e473771c ("Smack: Simplified Mandatory Access Control Kernel")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 2b79c30d4bb6b31678732526010d0ed1ddd39ed0..e22aad7604e8aca2cc6a291a2d824f2e0ed5e536 100644 (file)
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -896,7 +896,7 @@ static ssize_t smk_set_cipso(struct file *file, const char __user *buf,
        }
 
        ret = sscanf(rule, "%d", &catlen);
-       if (ret != 1 || catlen > SMACK_CIPSO_MAXCATNUM)
+       if (ret != 1 || catlen < 0 || catlen > SMACK_CIPSO_MAXCATNUM)
                goto out;
 
        if (format == SMK_FIXED24_FMT &&