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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        "Michael Kerrisk" <mtk.manpages@gmail.com>,
        "Kees Cook" <keescook@chromium.org>,
        "Eric Biggers" <ebiggers@google.com>,
        "Mikulas Patocka" <mpatocka@redhat.com>,
        "Willy Tarreau" <w@1wt.eu>,
        "Alexander Viro" <viro@zeniv.linux.org.uk>,
        "Joe Lawrence" <joe.lawrence@redhat.com>,
        "Linus Torvalds" <torvalds@linux-foundation.org>,
        "Luis R . Rodriguez" <mcgrof@kernel.org>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.310937469@decadent.org.uk>
Subject: [PATCH 3.16 213/410] pipe: fix off-by-one error when checking
 buffer limits
In-Reply-To: <lsq.1528380320.647747352@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

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

From: Eric Biggers <ebiggers@google.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@google.com>
Acked-by: Willy Tarreau <w@1wt.eu>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Luis R . Rodriguez" <mcgrof@kernel.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.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)