fs: prevent page refcount overflow in pipe_buf_get

Change pipe_buf_get() to return a bool indicating whether it succeeded
in raising the refcount of the page (if the thing in the pipe is a page).
This removes another mechanism for overflowing the page refcount.  All
callers converted to handle a failure.

Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 18 insertions, 10 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 809c0f2f9942..64f4de983468 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2034,10 +2034,8 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
 		rem += pipe->bufs[(pipe->curbuf + idx) & (pipe->buffers - 1)].len;
 
 	ret = -EINVAL;
-	if (rem < len) {
-		pipe_unlock(pipe);
-		goto out;
-	}
+	if (rem < len)
+		goto out_free;
 
 	rem = len;
 	while (rem) {
@@ -2055,7 +2053,9 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
 			pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
 			pipe->nrbufs--;
 		} else {
-			pipe_buf_get(pipe, ibuf);
+			if (!pipe_buf_get(pipe, ibuf))
+				goto out_free;
+
 			*obuf = *ibuf;
 			obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
 			obuf->len = rem;
@@ -2078,11 +2078,11 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
 	ret = fuse_dev_do_write(fud, &cs, len);
 
 	pipe_lock(pipe);
+out_free:
 	for (idx = 0; idx < nbuf; idx++)
 		pipe_buf_release(pipe, &bufs[idx]);
 	pipe_unlock(pipe);
 
-out:
 	kvfree(bufs);
 	return ret;
 }
diff --git a/fs/pipe.c b/fs/pipe.c
index bdc5d3c0977d..b1543b85c14a 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -189,9 +189,9 @@ EXPORT_SYMBOL(generic_pipe_buf_steal);
  *	in the tee() system call, when we duplicate the buffers in one
  *	pipe into another.
  */
-void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
+bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
 {
-	get_page(buf->page);
+	return try_get_page(buf->page);
 }
 EXPORT_SYMBOL(generic_pipe_buf_get);
 
diff --git a/fs/splice.c b/fs/splice.c
index de2ede048473..f30af82b850d 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1588,7 +1588,11 @@ retry:
 			 * Get a reference to this pipe buffer,
 			 * so we can copy the contents over.
 			 */
-			pipe_buf_get(ipipe, ibuf);
+			if (!pipe_buf_get(ipipe, ibuf)) {
+				if (ret == 0)
+					ret = -EFAULT;
+				break;
+			}
 			*obuf = *ibuf;
 
 			/*
@@ -1660,7 +1664,11 @@ static int link_pipe(struct pipe_inode_info *ipipe,
 		 * Get a reference to this pipe buffer,
 		 * so we can copy the contents over.
 		 */
-		pipe_buf_get(ipipe, ibuf);
+		if (!pipe_buf_get(ipipe, ibuf)) {
+			if (ret == 0)
+				ret = -EFAULT;
+			break;
+		}
 
 		obuf = opipe->bufs + nbuf;
 		*obuf = *ibuf;