proc mountinfo: make splice available again

stable inclusion
from stable-5.10.4
commit 54677c80ba1cfb47984c76d9d67d282dc5ce9fb9
bugzilla: 46903

--------------------------------

[ Upstream commit 14e3e989 ]

Since commit 36e2c742 ("fs: don't allow splice read/write without
explicit ops") we've required that file operation structures explicitly
enable splice support, rather than falling back to the default handlers.

Most /proc files use the indirect 'struct proc_ops' to describe their
file operations, and were fixed up to support splice earlier in commits
40be821d..b24c30c6, but the mountinfo files interact with the
VFS directly using their own 'struct file_operations' and got missed as
a result.

This adds the necessary support for splice to work for /proc/*/mountinfo
and friends.
Reported-by: NJoan Bruguera Micó <joanbrugueram@gmail.com>
Reported-by: NJussi Kivilinna <jussi.kivilinna@iki.fi>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=209971
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

fs/proc_namespace.c

@@ -320,7 +320,8 @@ static int mountstats_open(struct inode *inode, struct file *file)
 
 const struct file_operations proc_mounts_operations = {
 	.open		= mounts_open,
-	.read		= seq_read,
+	.read_iter	= seq_read_iter,
+	.splice_read	= generic_file_splice_read,
 	.llseek		= seq_lseek,
 	.release	= mounts_release,
 	.poll		= mounts_poll,
@@ -328,7 +329,8 @@ const struct file_operations proc_mounts_operations = {
 
 const struct file_operations proc_mountinfo_operations = {
 	.open		= mountinfo_open,
-	.read		= seq_read,
+	.read_iter	= seq_read_iter,
+	.splice_read	= generic_file_splice_read,
 	.llseek		= seq_lseek,
 	.release	= mounts_release,
 	.poll		= mounts_poll,
@@ -336,7 +338,8 @@ const struct file_operations proc_mountinfo_operations = {
 
 const struct file_operations proc_mountstats_operations = {
 	.open		= mountstats_open,
-	.read		= seq_read,
+	.read_iter	= seq_read_iter,
+	.splice_read	= generic_file_splice_read,
 	.llseek		= seq_lseek,
 	.release	= mounts_release,
 };