linux-kernel - [PATCH 3.16 215/410] pipe: simplify round_pipe

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Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Joe Lawrence" <joe.lawrence@...hat.com>,
        "Alexander Viro" <viro@...iv.linux.org.uk>,
        "Willy Tarreau" <w@....eu>,
        "Mikulas Patocka" <mpatocka@...hat.com>,
        "Eric Biggers" <ebiggers@...gle.com>,
        "Kees Cook" <keescook@...omium.org>,
        "Michael Kerrisk" <mtk.manpages@...il.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 215/410] pipe: simplify round_pipe_size()

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@...gle.com>

commit c4fed5a91fadc8a277b1eda474317b501651dd3e upstream.

round_pipe_size() calculates the number of pages the requested size
corresponds to, then rounds the page count up to the next power of 2.

However, it also rounds everything < PAGE_SIZE up to PAGE_SIZE.
Therefore, there's no need to actually translate the size into a page
count; we just need to round the size up to the next power of 2.

We do need to verify the size isn't greater than (1 << 31), since on
32-bit systems roundup_pow_of_two() would be undefined in that case.  But
that can just be combined with the UINT_MAX check which we need anyway
now.

Finally, update pipe_set_size() to not redundantly check the return value
of round_pipe_size() for the "invalid size" case twice.

Link: http://lkml.kernel.org/r/20180111052902.14409-7-ebiggers3@gmail.com
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Acked-by: Kees Cook <keescook@...omium.org>
Acked-by: Joe Lawrence <joe.lawrence@...hat.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: "Luis R . Rodriguez" <mcgrof@...nel.org>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
Cc: Mikulas Patocka <mpatocka@...hat.com>
Cc: Willy Tarreau <w@....eu>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/pipe.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1010,20 +1010,14 @@ const struct file_operations pipefifo_fo
  */
 unsigned int round_pipe_size(unsigned long size)
 {
-	unsigned long nr_pages;
-
-	if (size > UINT_MAX)
+	if (size > (1U << 31))
 		return 0;
 
 	/* Minimum pipe size, as required by POSIX */
 	if (size < PAGE_SIZE)
-		size = PAGE_SIZE;
-
-	nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
-	if (nr_pages == 0)
-		return 0;
+		return PAGE_SIZE;
 
-	return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
+	return roundup_pow_of_two(size);
 }
 
 /*
@@ -1038,8 +1032,6 @@ static long pipe_set_size(struct pipe_in
 	long ret = 0;
 
 	size = round_pipe_size(arg);
-	if (size == 0)
-		return -EINVAL;
 	nr_pages = size >> PAGE_SHIFT;
 
 	if (!nr_pages)