linux-kernel - [RFC PATCH 08/37] iov_iter_advance(): use consistent semantics for move past the end

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Date:   Sun,  6 Jun 2021 19:10:22 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Sterba <dsterba@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Anton Altaparmakov <anton@...era.com>,
        David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [RFC PATCH 08/37] iov_iter_advance(): use consistent semantics for move past the end

asking to advance by more than we have left in the iov_iter should
move to the very end; it should *not* leave negative i->count and
it should not spew into syslog, etc. - it's a legitimate operation.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 lib/iov_iter.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index a3aabeda945b..bdbe6691457d 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1117,8 +1117,6 @@ static inline void pipe_truncate(struct iov_iter *i)
 static void pipe_advance(struct iov_iter *i, size_t size)
 {
 	struct pipe_inode_info *pipe = i->pipe;
-	if (unlikely(i->count < size))
-		size = i->count;
 	if (size) {
 		struct pipe_buffer *buf;
 		unsigned int p_mask = pipe->ring_size - 1;
@@ -1159,6 +1157,8 @@ static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
 
 void iov_iter_advance(struct iov_iter *i, size_t size)
 {
+	if (unlikely(i->count < size))
+		size = i->count;
 	if (unlikely(iov_iter_is_pipe(i))) {
 		pipe_advance(i, size);
 		return;
@@ -1168,7 +1168,6 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
 		return;
 	}
 	if (unlikely(iov_iter_is_xarray(i))) {
-		size = min(size, i->count);
 		i->iov_offset += size;
 		i->count -= size;
 		return;
-- 
2.11.0