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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>
Subject: [PATCH 5.12 034/700] copy_page_to_iter(): fix ITER_DISCARD case
Date:   Mon, 12 Jul 2021 08:01:57 +0200
Message-Id: <20210712060929.437420872@linuxfoundation.org>
In-Reply-To: <20210712060924.797321836@linuxfoundation.org>
References: <20210712060924.797321836@linuxfoundation.org>
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From: Al Viro <viro@zeniv.linux.org.uk>

commit a506abc7b644d71966a75337d5a534f531b3cdc4 upstream.

we need to advance the iterator...

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 lib/iov_iter.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -906,9 +906,12 @@ size_t copy_page_to_iter(struct page *pa
 		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);