Patch "fs/pipe.c: return error code rather than 0 in pipe_write()" has been added to the 4.3-stable tree

This is a note to let you know that I've just added the patch titled

fs/pipe.c: return error code rather than 0 in pipe_write()

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fs-pipe.c-return-error-code-rather-than-0-in-pipe_write.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Biggers <[email protected]>
Date: Sat, 17 Oct 2015 16:26:09 -0500
Subject: fs/pipe.c: return error code rather than 0 in pipe_write()

From: Eric Biggers <[email protected]>

commit 6ae08069939f17422835448acae76bda8d96b16a upstream.

pipe_write() would return 0 if it failed to merge the beginning of the data to write with the last, partially filled pipe buffer. It should return an error code instead. Userspace programs could be confused by write() returning 0 when called with a nonzero 'count'.

The EFAULT error case was a regression from f0d1bec9d5 ("new helper:
copy_page_from_iter()"), while the ops->confirm() error case was a much older bug.

Test program:

	#include <assert.h>
	#include <errno.h>
	#include <unistd.h>

	int main(void)
	{
		int fd[2];
		char data[1] = {0};

		assert(0 == pipe(fd));
		assert(1 == write(fd[1], data, 1));

		/* prior to this patch, write() returned 0 here  */
		assert(-1 == write(fd[1], NULL, 1));
		assert(errno == EFAULT);
	}

---
 fs/pipe.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

@@ -366,18 +366,17 @@ pipe_write(struct kiocb *iocb, struct io
 		int offset = buf->offset + buf->len;
 
 		if (ops->can_merge && offset + chars <= PAGE_SIZE) {
-			int error = ops->confirm(pipe, buf);
-			if (error)
+			ret = ops->confirm(pipe, buf);
+			if (ret)
 				goto out;
 
 			ret = copy_page_from_iter(buf->page, offset, chars, from);
 			if (unlikely(ret < chars)) {
-				error = -EFAULT;
+				ret = -EFAULT;
 				goto out;
 			}
 			do_wakeup = 1;
-			buf->len += chars;
-			ret = chars;
+			buf->len += ret;
 			if (!iov_iter_count(from))
 				goto out;
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/fs-pipe.c-return-error-code-rather-than-0-in-pipe_write.patch