From nobody Thu Dec 18 14:28:52 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 25744C4167B for ; Sat, 2 Dec 2023 01:02:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1441997AbjLBBBy (ORCPT ); Fri, 1 Dec 2023 20:01:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41896 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229456AbjLBBBv (ORCPT ); Fri, 1 Dec 2023 20:01:51 -0500 Received: from abb.hmeau.com (abb.hmeau.com [144.6.53.87]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 28D35B6; Fri, 1 Dec 2023 17:01:56 -0800 (PST) Received: from loth.rohan.me.apana.org.au ([192.168.167.2]) by formenos.hmeau.com with smtp (Exim 4.94.2 #2 (Debian)) id 1r9EO9-005zG6-86; Sat, 02 Dec 2023 09:01:46 +0800 Received: by loth.rohan.me.apana.org.au (sSMTP sendmail emulation); Sat, 02 Dec 2023 09:01:54 +0800 Date: Sat, 2 Dec 2023 09:01:54 +0800 From: Herbert Xu To: Edward Adam Davis Cc: davem@davemloft.net, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, olivia@selenic.com, syzbot+c52ab18308964d248092@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com, Ian Molton , Rusty Russell Subject: [PATCH] hwrng: core - Fix page fault dead lock on mmap-ed hwrng Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" There is a dead-lock in the hwrng device read path. This triggers when the user reads from /dev/hwrng into memory also mmap-ed from /dev/hwrng. The resulting page fault triggers a recursive read which then dead-locks. Fix this by using a stack buffer when calling copy_to_user. Reported-by: Edward Adam Davis Reported-by: syzbot+c52ab18308964d248092@syzkaller.appspotmail.com Fixes: 9996508b3353 ("hwrng: core - Replace u32 in driver API with byte arr= ay") Cc: Signed-off-by: Herbert Xu diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 420f155d251f..a3bbdd6e60fc 100644 Reviewed-by: PrasannaKumar Muralidharan --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -23,10 +23,13 @@ #include #include #include +#include #include =20 #define RNG_MODULE_NAME "hw_random" =20 +#define RNG_BUFFER_SIZE (SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES) + static struct hwrng *current_rng; /* the current rng has been explicitly chosen by user via sysfs */ static int cur_rng_set_by_user; @@ -58,7 +61,7 @@ static inline int rng_get_data(struct hwrng *rng, u8 *buf= fer, size_t size, =20 static size_t rng_buffer_size(void) { - return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES; + return RNG_BUFFER_SIZE; } =20 static void add_early_randomness(struct hwrng *rng) @@ -209,6 +212,7 @@ static inline int rng_get_data(struct hwrng *rng, u8 *b= uffer, size_t size, static ssize_t rng_dev_read(struct file *filp, char __user *buf, size_t size, loff_t *offp) { + u8 buffer[RNG_BUFFER_SIZE]; ssize_t ret =3D 0; int err =3D 0; int bytes_read, len; @@ -236,34 +240,37 @@ static ssize_t rng_dev_read(struct file *filp, char _= _user *buf, if (bytes_read < 0) { err =3D bytes_read; goto out_unlock_reading; - } - data_avail =3D bytes_read; - } - - if (!data_avail) { - if (filp->f_flags & O_NONBLOCK) { + } else if (bytes_read =3D=3D 0 && + (filp->f_flags & O_NONBLOCK)) { err =3D -EAGAIN; goto out_unlock_reading; } - } else { - len =3D data_avail; + + data_avail =3D bytes_read; + } + + len =3D data_avail; + if (len) { if (len > size) len =3D size; =20 data_avail -=3D len; =20 - if (copy_to_user(buf + ret, rng_buffer + data_avail, - len)) { + memcpy(buffer, rng_buffer + data_avail, len); + } + mutex_unlock(&reading_mutex); + put_rng(rng); + + if (len) { + if (copy_to_user(buf + ret, buffer, len)) { err =3D -EFAULT; - goto out_unlock_reading; + goto out; } =20 size -=3D len; ret +=3D len; } =20 - mutex_unlock(&reading_mutex); - put_rng(rng); =20 if (need_resched()) schedule_timeout_interruptible(1); @@ -274,6 +281,7 @@ static ssize_t rng_dev_read(struct file *filp, char __u= ser *buf, } } out: + memzero_explicit(buffer, sizeof(buffer)); return ret ? : err; =20 out_unlock_reading: --=20 Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt