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From: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
To: penguin-kernel@i-love.sakura.ne.jp
Cc: andreyknvl@google.com, casey@schaufler-ca.com, jmorris@namei.org,
	linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org, mhocko@suse.com,
	serge@hallyn.com, snovitoll@gmail.com,
	syzbot+a71a442385a0b2815497@syzkaller.appspotmail.com
Subject: [PATCH v2] smackfs: restrict bytes count in smackfs write functions
Date: Thu, 28 Jan 2021 17:58:01 +0600	[thread overview]
Message-ID: <20210128115801.1096425-1-snovitoll@gmail.com> (raw)
In-Reply-To: <3c35f7cc-1c8d-2fa0-6bc9-bde4e96017ce@i-love.sakura.ne.jp>

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 than PAGE_SIZE.

Per smackfs doc, smk_write_net4addr accepts any label or -CIPSO,
smk_write_net6addr accepts any label or -DELETE. I couldn't find
any general rule for other label lengths except SMK_LABELLEN,
SMK_LONGLABEL, SMK_CIPSOMAX which are documented.

Let's constrain, in general, smackfs label lengths for PAGE_SIZE.
Although fuzzer crashes write to smackfs/netlabel on 0x400000 length.

Here is a quick way to reproduce the WARNING:
python -c "print('A' * 0x400000)" > /sys/fs/smackfs/netlabel

Reported-by: syzbot+a71a442385a0b2815497@syzkaller.appspotmail.com
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
---
 security/smack/smackfs.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 5d44b7d258ef..22ded2c26089 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 > PAGE_SIZE - 1)
 		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 > PAGE_SIZE - 1)
 		return -EINVAL;
 
 	data = memdup_user_nul(buf, count);
@@ -1834,6 +1834,10 @@ static ssize_t smk_write_ambient(struct file *file, const char __user *buf,
 	if (!smack_privileged(CAP_MAC_ADMIN))
 		return -EPERM;
 
+	/* Enough data must be present */
+	if (count == 0 || count > PAGE_SIZE)
+		return -EINVAL;
+
 	data = memdup_user_nul(buf, count);
 	if (IS_ERR(data))
 		return PTR_ERR(data);
@@ -2005,6 +2009,9 @@ static ssize_t smk_write_onlycap(struct file *file, const char __user *buf,
 	if (!smack_privileged(CAP_MAC_ADMIN))
 		return -EPERM;
 
+	if (count > PAGE_SIZE)
+		return -EINVAL;
+
 	data = memdup_user_nul(buf, count);
 	if (IS_ERR(data))
 		return PTR_ERR(data);
@@ -2092,6 +2099,9 @@ static ssize_t smk_write_unconfined(struct file *file, const char __user *buf,
 	if (!smack_privileged(CAP_MAC_ADMIN))
 		return -EPERM;
 
+	if (count > PAGE_SIZE)
+		return -EINVAL;
+
 	data = memdup_user_nul(buf, count);
 	if (IS_ERR(data))
 		return PTR_ERR(data);
@@ -2648,6 +2658,10 @@ static ssize_t smk_write_syslog(struct file *file, const char __user *buf,
 	if (!smack_privileged(CAP_MAC_ADMIN))
 		return -EPERM;
 
+	/* Enough data must be present */
+	if (count == 0 || count > PAGE_SIZE)
+		return -EINVAL;
+
 	data = memdup_user_nul(buf, count);
 	if (IS_ERR(data))
 		return PTR_ERR(data);
@@ -2740,10 +2754,13 @@ static ssize_t smk_write_relabel_self(struct file *file, const char __user *buf,
 		return -EPERM;
 
 	/*
+	 * No partial write.
 	 * Enough data must be present.
 	 */
 	if (*ppos != 0)
 		return -EINVAL;
+	if (count == 0 || count > PAGE_SIZE)
+		return -EINVAL;
 
 	data = memdup_user_nul(buf, count);
 	if (IS_ERR(data))
-- 
2.25.1


  reply	other threads:[~2021-01-28 11:59 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-24 14:36 [PATCH] smackfs: restrict bytes count in smackfs write functions Sabyrzhan Tasbolatov
2021-01-25 18:08 ` Casey Schaufler
2021-01-25 22:42   ` Tetsuo Handa
2021-01-28 11:58     ` Sabyrzhan Tasbolatov [this message]
2021-01-28 12:59       ` [PATCH v2] " Tetsuo Handa
2021-01-28 13:27         ` Sabyrzhan Tasbolatov
2021-01-28 14:24           ` Tetsuo Handa
2021-01-29  2:10             ` Casey Schaufler
2021-02-02 19:13               ` Sabyrzhan Tasbolatov
2021-02-02 19:33                 ` Casey Schaufler

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