linux-kernel - [PATCH 4.14 284/343] Partially revert "kfifo: fix kfifo_alloc() and kfifo

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 24 Jan 2020 10:31:42 +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, laokz <laokz@...mail.com>,
        Stefani Seibold <stefani@...bold.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Greg KH <greg@...ah.com>, Kees Cook <keescook@...omium.org>,
        Will Deacon <will@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 284/343] Partially revert "kfifo: fix kfifo_alloc() and kfifo_init()"

From: Linus Torvalds <torvalds@...ux-foundation.org>

[ Upstream commit ab9bb6318b0967671e0c9b6537c1537d51ca4f45 ]

Commit dfe2a77fd243 ("kfifo: fix kfifo_alloc() and kfifo_init()") made
the kfifo code round the number of elements up.  That was good for
__kfifo_alloc(), but it's actually wrong for __kfifo_init().

The difference? __kfifo_alloc() will allocate the rounded-up number of
elements, but __kfifo_init() uses an allocation done by the caller.  We
can't just say "use more elements than the caller allocated", and have
to round down.

The good news? All the normal cases will be using power-of-two arrays
anyway, and most users of kfifo's don't use kfifo_init() at all, but one
of the helper macros to declare a KFIFO that enforce the proper
power-of-two behavior.  But it looks like at least ibmvscsis might be
affected.

The bad news? Will Deacon refers to an old thread and points points out
that the memory ordering in kfifo's is questionable.  See

  https://lore.kernel.org/lkml/20181211034032.32338-1-yuleixzhang@tencent.com/

for more.

Fixes: dfe2a77fd243 ("kfifo: fix kfifo_alloc() and kfifo_init()")
Reported-by: laokz <laokz@...mail.com>
Cc: Stefani Seibold <stefani@...bold.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dan Carpenter <dan.carpenter@...cle.com>
Cc: Greg KH <greg@...ah.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Will Deacon <will@...nel.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 lib/kfifo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/kfifo.c b/lib/kfifo.c
index 90ba1eb1df06e..a94227c555510 100644
--- a/lib/kfifo.c
+++ b/lib/kfifo.c
@@ -82,7 +82,8 @@ int __kfifo_init(struct __kfifo *fifo, void *buffer,
 {
 	size /= esize;

-	size = roundup_pow_of_two(size);
+	if (!is_power_of_2(size))
+		size = rounddown_pow_of_two(size);

 	fifo->in = 0;
 	fifo->out = 0;
-- 
2.20.1