linux-kernel - [PATCH 1/2] Smack: fix another vsscanf out of bounds

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Date:   Thu, 23 Jul 2020 18:22:19 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: [PATCH 1/2] Smack: fix another vsscanf out of bounds

This is similar to commit 84e99e58e8d1 ("Smack: slab-out-of-bounds in
vsscanf") where we added a bounds check on "rule".

Reported-by: syzbot+a22c6092d003d6fe1122@...kaller.appspotmail.com
Fixes: f7112e6c9abf ("Smack: allow for significantly longer Smack labels v4")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
This check is very straight forward and should fix the bug.  But if you
look at the fixes tag we used to rely on the check:

	if (count != (SMK_CIPSOMIN + catlen * SMK_DIGITLEN))

and now that has been changed to:

	if (format == SMK_FIXED24_FMT &&
	    count != (SMK_CIPSOMIN + catlen * SMK_DIGITLEN))
                goto out;

so it doesn't apply for every format.

 security/smack/smackfs.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index c21b656b3263..81c6ceeaa4f9 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -905,6 +905,10 @@ static ssize_t smk_set_cipso(struct file *file, const char __user *buf,
 
 	for (i = 0; i < catlen; i++) {
 		rule += SMK_DIGITLEN;
+		if (rule > data + count) {
+			rc = -EOVERFLOW;
+			goto out;
+		}
 		ret = sscanf(rule, "%u", &cat);
 		if (ret != 1 || cat > SMACK_CIPSO_MAXCATNUM)
 			goto out;
-- 
2.27.0