From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-cys01nam02on0101.outbound.protection.outlook.com ([104.47.37.101]:1938 "EHLO NAM02-CY1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S966839AbeCSQM6 (ORCPT ); Mon, 19 Mar 2018 12:12:58 -0400 From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: Michael Schmitz , Theodore Ts'o , Sasha Levin Subject: [PATCH AUTOSEL for 3.18 044/102] fix race in drivers/char/random.c:get_reg() Date: Mon, 19 Mar 2018 16:12:26 +0000 Message-ID: <20180319161117.17833-44-alexander.levin@microsoft.com> References: <20180319161117.17833-1-alexander.levin@microsoft.com> In-Reply-To: <20180319161117.17833-1-alexander.levin@microsoft.com> Content-Language: en-US Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org List-ID: 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 --- drivers/char/random.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index d55156fc064d..73049abf4898 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -863,12 +863,16 @@ static void add_interrupt_bench(cycles_t start) static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs) { __u32 *ptr =3D (__u32 *) regs; + unsigned long flags; =20 if (regs =3D=3D NULL) return 0; + local_irq_save(flags); if (f->reg_idx >=3D sizeof(struct pt_regs) / sizeof(__u32)) f->reg_idx =3D 0; - return *(ptr + f->reg_idx++); + ptr +=3D f->reg_idx++; + local_irq_restore(flags); + return *ptr; } =20 void add_interrupt_randomness(int irq, int irq_flags) --=20 2.14.1