[PATCH 12/44] printk: /dev/kmsg - properly support writev() to avoid interleaved printk() lines

Greg Kroah-Hartman
2011-05-20T00:19:32Z

From: Kay Sievers <kay.sievers@vrfy.org>

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>
---
drivers/char/mem.c | 41 ++++++++++++++++++++++++++---------------
1 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 436a990..78923a9 100644
--- 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,
};

--
1.7.4.2