linux-kernel - [PATCH] smackfs: restrict bytes count in smackfs write functions

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Date:   Sun, 24 Jan 2021 20:36:27 +0600
From:   Sabyrzhan Tasbolatov <snovitoll@...il.com>
To:     casey@...aufler-ca.com
Cc:     jmorris@...ei.org, serge@...lyn.com, andreyknvl@...gle.com,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+a71a442385a0b2815497@...kaller.appspotmail.com
Subject: [PATCH] smackfs: restrict bytes count in smackfs write functions

syzbot found WARNINGs in several smackfs write operations where
bytes count is passed to memdup_user_nul which exceeds
GFP MAX_ORDER. Check count size if bigger SMK_LONGLABEL,
for smk_write_syslog if bigger than PAGE_SIZE - 1.

Reported-by: syzbot+a71a442385a0b2815497@...kaller.appspotmail.com
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@...il.com>
---
 security/smack/smackfs.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 5d44b7d258ef..88678c6f1b8c 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -1167,7 +1167,7 @@ static ssize_t smk_write_net4addr(struct file *file, const char __user *buf,
 		return -EPERM;
 	if (*ppos != 0)
 		return -EINVAL;
-	if (count < SMK_NETLBLADDRMIN)
+	if (count < SMK_NETLBLADDRMIN || count > SMK_LONGLABEL)
 		return -EINVAL;
 
 	data = memdup_user_nul(buf, count);
@@ -1427,7 +1427,7 @@ static ssize_t smk_write_net6addr(struct file *file, const char __user *buf,
 		return -EPERM;
 	if (*ppos != 0)
 		return -EINVAL;
-	if (count < SMK_NETLBLADDRMIN)
+	if (count < SMK_NETLBLADDRMIN || count > SMK_LONGLABEL)
 		return -EINVAL;
 
 	data = memdup_user_nul(buf, count);
@@ -2647,6 +2647,8 @@ static ssize_t smk_write_syslog(struct file *file, const char __user *buf,
 
 	if (!smack_privileged(CAP_MAC_ADMIN))
 		return -EPERM;
+	if (count > PAGE_SIZE - 1)
+		return -EINVAL;
 
 	data = memdup_user_nul(buf, count);
 	if (IS_ERR(data))
@@ -2744,6 +2746,8 @@ static ssize_t smk_write_relabel_self(struct file *file, const char __user *buf,
 	 */
 	if (*ppos != 0)
 		return -EINVAL;
+	if (count > SMK_LONGLABEL)
+		return -EINVAL;
 
 	data = memdup_user_nul(buf, count);
 	if (IS_ERR(data))
-- 
2.25.1