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 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>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 5d44b7d258ef00fe4388242aac5949fc7ac67734..22ded2c26089c10610f99c6f91c0d7dc500e0a88 100644 (file)
--- 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))