Re: [RFC][PATCH 1/1] support for user-space buffers in kfifo

[Nelson Castillo]

On 6/12/07, Stelian Pop <stelian@xxxxxxxxxx> wrote:
(cut)
> accessing userspace memory with a spinlock taken (moreover an
> irqsave()
> one) is bad bad bad.

Hi Stelian.

I'm sending the new patch without kfifo_put_user and kfifo_get_user.

Regards,
Nelson.-

Signed-off-by: Nelson Castillo <nelson@xxxxxxxxxx>
---
diff --git a/include/linux/kfifo.h b/include/linux/kfifo.h
index 404f446..5c4c416 100644
--- a/include/linux/kfifo.h
+++ b/include/linux/kfifo.h
@@ -41,8 +41,13 @@ extern struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask,
 extern void kfifo_free(struct kfifo *fifo);
 extern unsigned int __kfifo_put(struct kfifo *fifo,
 				unsigned char *buffer, unsigned int len);
+extern int __kfifo_put_user(struct kfifo *fifo,
+			    const unsigned char __user *buffer,
+			    unsigned int len);
 extern unsigned int __kfifo_get(struct kfifo *fifo,
 				unsigned char *buffer, unsigned int len);
+extern int __kfifo_get_user(struct kfifo *fifo,  unsigned char __user *buffer,
+			    unsigned int len);
 
 /**
  * __kfifo_reset - removes the entire FIFO contents, no locking version
diff --git a/kernel/kfifo.c b/kernel/kfifo.c
index cee4191..41438ec 100644
--- a/kernel/kfifo.c
+++ b/kernel/kfifo.c
@@ -23,6 +23,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/err.h>
+#include <asm/uaccess.h>
 #include <linux/kfifo.h>
 
 /**
@@ -150,6 +151,61 @@ unsigned int __kfifo_put(struct kfifo *fifo,
 EXPORT_SYMBOL(__kfifo_put);
 
 /**
+ * __kfifo_put_user - puts some data into the FIFO, from userspace
+ *		      We don't have a locking version because copy_from_user
+ *		      might sleep and you must not sleep holding a spinlock.
+ *
+ * @fifo: the fifo to be used.
+ * @buffer: the user space data to be added.
+ * @len: the length of the data to be added.
+ *
+ * This function copies at most @len bytes from the @buffer into
+ * the FIFO depending on the free space, and returns the number of
+ * bytes copied.
+ *
+ * Note that with only one concurrent reader and one concurrent
+ * writer, you don't need extra locking to use these functions.
+ */
+int __kfifo_put_user(struct kfifo *fifo, const unsigned char __user *buffer,
+	        unsigned int len)
+{
+	unsigned int l;
+
+	len = min(len, fifo->size - fifo->in + fifo->out);
+
+	/*
+	 * Ensure that we sample the fifo->out index -before- we
+	 * start putting bytes into the kfifo.
+	 */
+
+	smp_mb();
+
+	/* first put the data starting from fifo->in to buffer end */
+	l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
+
+	if(copy_from_user(fifo->buffer + (fifo->in & (fifo->size - 1)),
+			  buffer, l))
+		return  -EFAULT;
+
+
+	/* then put the rest (if any) at the beginning of the buffer */
+	if (copy_from_user(fifo->buffer, buffer + l, len - l))
+		return  -EFAULT;
+
+	/*
+	 * Ensure that we add the bytes to the kfifo -before-
+	 * we update the fifo->in index.
+	 */
+
+	smp_wmb();
+
+	fifo->in += len;
+
+	return (int)len;
+}
+EXPORT_SYMBOL(__kfifo_put_user);
+
+/**
  * __kfifo_get - gets some data from the FIFO, no locking version
  * @fifo: the fifo to be used.
  * @buffer: where the data must be copied.
@@ -194,3 +250,56 @@ unsigned int __kfifo_get(struct kfifo *fifo,
 	return len;
 }
 EXPORT_SYMBOL(__kfifo_get);
+
+/**
+ * __kfifo_get_user - gets some data from the FIFO to userspace
+ *		      We don't have a locking version because copy_to_user
+ *		      might sleep and you must not sleep holding a spinlock.
+ * @fifo: the fifo to be used.
+ * @buffer: user space buffer where the data must be copied.
+ * @len: the size of the destination buffer.
+ *
+ * This function copies at most @len bytes from the FIFO into the
+ * @buffer and returns the number of copied bytes.
+ *
+ * Note that with only one concurrent reader and one concurrent
+ * writer, you don't need extra locking to use these functions.
+ */
+
+int __kfifo_get_user(struct kfifo *fifo,
+			 unsigned char __user *buffer, unsigned int len)
+{
+	unsigned int l;
+
+	len = min(len, fifo->in - fifo->out);
+
+	/*
+	 * Ensure that we sample the fifo->in index -before- we
+	 * start removing bytes from the kfifo.
+	 */
+
+	smp_rmb();
+
+	/* first get the data from fifo->out until the end of the buffer */
+	l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));
+
+	if (copy_to_user(buffer, fifo->buffer + (fifo->out & (fifo->size - 1)), l))
+		return -EFAULT;
+
+	/* then get the rest (if any) from the beginning of the buffer */
+	if (copy_to_user(buffer + l, fifo->buffer, len - l))
+		return -EFAULT;
+
+	/*
+	 * Ensure that we remove the bytes from the kfifo -before-
+	 * we update the fifo->out index.
+	 */
+
+	smp_mb();
+
+	fifo->out += len;
+
+	return (int)len;
+}
+EXPORT_SYMBOL(__kfifo_get_user);
+

-- 

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