From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Miklos Szeredi <mszeredi@redhat.com>,
        Stan Hu <stanhu@gmail.com>
Subject: [PATCH 5.10 003/130] ovl: simplify file splice
Date:   Mon,  6 Dec 2021 15:55:20 +0100
Message-Id: <20211206145559.731406260@linuxfoundation.org>
In-Reply-To: <20211206145559.607158688@linuxfoundation.org>
References: <20211206145559.607158688@linuxfoundation.org>
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From: Miklos Szeredi <mszeredi@redhat.com>

commit 82a763e61e2b601309d696d4fa514c77d64ee1be upstream.

generic_file_splice_read() and iter_file_splice_write() will call back into
f_op->iter_read() and f_op->iter_write() respectively.  These already do
the real file lookup and cred override.  So the code in ovl_splice_read()
and ovl_splice_write() is redundant.

In addition the ovl_file_accessed() call in ovl_splice_write() is
incorrect, though probably harmless.

Fix by calling generic_file_splice_read() and iter_file_splice_write()
directly.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: Stan Hu <stanhu@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/overlayfs/file.c |   46 ++--------------------------------------------
 1 file changed, 2 insertions(+), 44 deletions(-)

--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -422,48 +422,6 @@ out_unlock:
 	return ret;
 }
 
-static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
-			 struct pipe_inode_info *pipe, size_t len,
-			 unsigned int flags)
-{
-	ssize_t ret;
-	struct fd real;
-	const struct cred *old_cred;
-
-	ret = ovl_real_fdget(in, &real);
-	if (ret)
-		return ret;
-
-	old_cred = ovl_override_creds(file_inode(in)->i_sb);
-	ret = generic_file_splice_read(real.file, ppos, pipe, len, flags);
-	revert_creds(old_cred);
-
-	ovl_file_accessed(in);
-	fdput(real);
-	return ret;
-}
-
-static ssize_t
-ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
-			  loff_t *ppos, size_t len, unsigned int flags)
-{
-	struct fd real;
-	const struct cred *old_cred;
-	ssize_t ret;
-
-	ret = ovl_real_fdget(out, &real);
-	if (ret)
-		return ret;
-
-	old_cred = ovl_override_creds(file_inode(out)->i_sb);
-	ret = iter_file_splice_write(pipe, real.file, ppos, len, flags);
-	revert_creds(old_cred);
-
-	ovl_file_accessed(out);
-	fdput(real);
-	return ret;
-}
-
 static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 {
 	struct fd real;
@@ -772,8 +730,8 @@ const struct file_operations ovl_file_op
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= ovl_compat_ioctl,
 #endif
-	.splice_read    = ovl_splice_read,
-	.splice_write   = ovl_splice_write,
+	.splice_read    = generic_file_splice_read,
+	.splice_write   = iter_file_splice_write,
 
 	.copy_file_range	= ovl_copy_file_range,
 	.remap_file_range	= ovl_remap_file_range,