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From:   Souptick Joarder <jrdr.linux@gmail.com>
To:     akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Souptick Joarder <jrdr.linux@gmail.com>,
        John Hubbard <jhubbard@nvidia.com>
Subject: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
Date:   Sun, 13 Sep 2020 20:02:35 +0530
Message-Id: <1600007555-11650-1-git-send-email-jrdr.linux@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

It is possible that a buggy caller of unpin_user_pages()
(specially in error handling path) may end up calling it with
npages < 0 which is unnecessary.

This can be fixed by adding extra check inside unpin_user_pages().

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Cc: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 0b5c308b..2e19bd6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
 {
 	unsigned long index;
 
+	if (WARN_ON_ONCE(npages < 0))
+		return;
+
 	/*
 	 * TODO: this can be optimized for huge pages: if a series of pages is
 	 * physically contiguous and part of the same compound page, then a
-- 
1.9.1