From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:36834 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933995AbeDKS6w (ORCPT ); Wed, 11 Apr 2018 14:58:52 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Michael Schmitz , Theodore Tso , Sasha Levin Subject: [PATCH 4.9 106/310] fix race in drivers/char/random.c:get_reg() Date: Wed, 11 Apr 2018 20:34:05 +0200 Message-Id: <20180411183626.773044501@linuxfoundation.org> In-Reply-To: <20180411183622.305902791@linuxfoundation.org> References: <20180411183622.305902791@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michael Schmitz [ Upstream commit 9dfa7bba35ac08a63565d58c454dccb7e1bb0a08 ] get_reg() can be reentered on architectures with prioritized interrupts (m68k in this case), causing f->reg_index to be incremented after the range check. Out of bounds memory access past the pt_regs struct results. This will go mostly undetected unless access is beyond end of memory. Prevent the race by disabling interrupts in get_reg(). Tested on m68k (Atari Falcon, and ARAnyM emulator). Kudos to Geert Uytterhoeven for helping to trace this race. Signed-off-by: Michael Schmitz Signed-off-by: Theodore Ts'o Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1115,12 +1115,16 @@ static void add_interrupt_bench(cycles_t static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs) { __u32 *ptr = (__u32 *) regs; + unsigned long flags; if (regs == NULL) return 0; + local_irq_save(flags); if (f->reg_idx >= sizeof(struct pt_regs) / sizeof(__u32)) f->reg_idx = 0; - return *(ptr + f->reg_idx++); + ptr += f->reg_idx++; + local_irq_restore(flags); + return *ptr; } void add_interrupt_randomness(int irq, int irq_flags)