linux-kernel - [PATCH 4.9 65/88] pipe: fix off-by-one error when checking buffer limits

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Date:   Thu, 15 Feb 2018 16:17:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>,
        Willy Tarreau <w@....eu>, Kees Cook <keescook@...omium.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 65/88] pipe: fix off-by-one error when checking buffer limits

4.9-stable 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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/pipe.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -609,12 +609,12 @@ 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)