From 6ae08069939f17422835448acae76bda8d96b16a Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers3@gmail.com>
Date: Sat, 17 Oct 2015 16:26:09 -0500
Subject: [PATCH] fs/pipe.c: return error code rather than 0 in pipe_write()
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);
}
Cc: stable@vger.kernel.org # at least v3.15+
Signed-off-by: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/pipe.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c
index 997de3464479..42cf8ddf0e55 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -366,18 +366,17 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
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;
}