printk: /dev/kmsg - properly support writev() to avoid interleaved printk() lines

printk: /dev/kmsg - properly support writev() to avoid interleaved printk lines

We should avoid calling printk() in a loop, when we pass a single
string to /dev/kmsg with writev().

Cc: Lennart Poettering <lennart@poettering.net>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 436a990179988a06fb10e18884cb9db56371fdb5..78923a9f534522c7737de57f0918b81fa53a7201 100644 (file)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -806,29 +806,40 @@ static const struct file_operations oldmem_fops = {
 };
 #endif
 
-static ssize_t kmsg_write(struct file *file, const char __user *buf,
-                         size_t count, loff_t *ppos)
+static ssize_t kmsg_writev(struct kiocb *iocb, const struct iovec *iv,
+                          unsigned long count, loff_t pos)
 {
-       char *tmp;
-       ssize_t ret;
+       char *line, *p;
+       int len, i;
+       ssize_t ret = -EFAULT;
 
-       tmp = kmalloc(count + 1, GFP_KERNEL);
-       if (tmp == NULL)
+       len = iov_length(iv, count);
+       line = p = kmalloc(len + 1, GFP_KERNEL);
+       if (line == NULL)
                return -ENOMEM;
-       ret = -EFAULT;
-       if (!copy_from_user(tmp, buf, count)) {
-               tmp[count] = 0;
-               ret = printk("%s", tmp);
-               if (ret > count)
-                       /* printk can add a prefix */
-                       ret = count;
+
+       /*
+        * copy all vectors into a single string, to ensure we do
+        * not interleave our log line with other printk calls
+        */
+       for (i = 0; i < count; i++) {
+               if (copy_from_user(p, iv[i].iov_base, iv[i].iov_len))
+                       goto out;
+               p += iv[i].iov_len;
        }
-       kfree(tmp);
+       p[0] = '\0';
+
+       ret = printk("%s", line);
+       /* printk can add a prefix */
+       if (ret > len)
+               ret = len;
+out:
+       kfree(line);
        return ret;
 }
 
 static const struct file_operations kmsg_fops = {
-       .write = kmsg_write,
+       .aio_write = kmsg_writev,
        .llseek = noop_llseek,
 };