linux-kernel - [PATCH 3.16 213/410] pipe: fix off-by-one error when checking buffer limits

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Message-ID: <lsq.1528380321.310937469@decadent.org.uk>
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,
        "Michael Kerrisk" <mtk.manpages@...il.com>,
        "Kees Cook" <keescook@...omium.org>,
        "Eric Biggers" <ebiggers@...gle.com>,
        "Mikulas Patocka" <mpatocka@...hat.com>,
        "Willy Tarreau" <w@....eu>,
        "Alexander Viro" <viro@...iv.linux.org.uk>,
        "Joe Lawrence" <joe.lawrence@...hat.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>
Subject: [PATCH 3.16 213/410] pipe: fix off-by-one error when checking
 buffer limits

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

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

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

commit 9903a91c763ecdae333a04a9d89d79d2b8966503 upstream.

With pipe-user-pages-hard set to 'N', users were actually only allowed up
to 'N - 1' buffers; and likewise for pipe-user-pages-soft.

Fix this to allow up to 'N' buffers, as would be expected.

Link: http://lkml.kernel.org/r/20180111052902.14409-5-ebiggers3@gmail.com
Fixes: b0b91d18e2e9 ("pipe: fix limit checking in pipe_set_size()")
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Acked-by: Willy Tarreau <w@....eu>
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>
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 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -593,12 +593,12 @@ static unsigned long account_pipe_buffer
 
 static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
 {
-	return pipe_user_pages_soft && user_bufs >= pipe_user_pages_soft;
+	return pipe_user_pages_soft && user_bufs > pipe_user_pages_soft;
 }
 
 static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
 {
-	return pipe_user_pages_hard && user_bufs >= pipe_user_pages_hard;
+	return pipe_user_pages_hard && user_bufs > pipe_user_pages_hard;
 }
 
 static bool is_unprivileged_user(void)