linux-kernel - [RFC PATCH 06/37] copy_page_to_iter(): fix ITER

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Date:   Sun,  6 Jun 2021 19:10:20 +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 06/37] copy_page_to_iter(): fix ITER_DISCARD case

we need to advance the iterator...

Cc: stable@...r.kernel.org
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 lib/iov_iter.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 12fb04b23143..c8877cffb7bc 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -965,9 +965,12 @@ static size_t __copy_page_to_iter(struct page *page, size_t offset, size_t bytes
 		size_t wanted = copy_to_iter(kaddr + offset, bytes, i);
 		kunmap_atomic(kaddr);
 		return wanted;
-	} else if (unlikely(iov_iter_is_discard(i)))
+	} else if (unlikely(iov_iter_is_discard(i))) {
+		if (unlikely(i->count < bytes))
+			bytes = i->count;
+		i->count -= bytes;
 		return bytes;
-	else if (likely(!iov_iter_is_pipe(i)))
+	} else if (likely(!iov_iter_is_pipe(i)))
 		return copy_page_to_iter_iovec(page, offset, bytes, i);
 	else
 		return copy_page_to_iter_pipe(page, offset, bytes, i);
-- 
2.11.0