linux-kernel - [PATCH] mm/gup.c: Handle error at earliest for incorrect nr

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Date:   Fri,  1 May 2020 01:41:58 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Souptick Joarder <jrdr.linux@...il.com>
Subject: [PATCH] mm/gup.c: Handle error at earliest for incorrect nr_pages value

As per documentation, pin_user_pages_fast() & get_user_pages_fast()
will return 0, if nr_pages <= 0. But this can be figure out only after
going inside the internal_get_user_pages_fast().

This can be handled early. Adding a check for the same.

Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
---
 mm/gup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 50681f0..a13aaa6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2817,6 +2817,8 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 	 */
 	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
 		return -EINVAL;
+	if (nr_pages <= 0)
+		return 0;
 
 	/*
 	 * The caller may or may not have explicitly set FOLL_GET; either way is
@@ -2854,6 +2856,8 @@ int pin_user_pages_fast(unsigned long start, int nr_pages,
 	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
 	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
 		return -EINVAL;
+	if (nr_pages <= 0)
+		return 0;
 
 	gup_flags |= FOLL_PIN;
 	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
-- 
1.9.1