From nobody Mon Apr 13 13:30:26 2026 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 CFA11C433FE for ; Wed, 12 Oct 2022 10:45:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229773AbiJLKph (ORCPT ); Wed, 12 Oct 2022 06:45:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35718 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229704AbiJLKpY (ORCPT ); Wed, 12 Oct 2022 06:45:24 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 967DB4D82F; Wed, 12 Oct 2022 03:45:22 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 26890CE1B07; Wed, 12 Oct 2022 10:45:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BD21C4347C; Wed, 12 Oct 2022 10:45:19 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.96) (envelope-from ) id 1oiZF0-0047St-3C; Wed, 12 Oct 2022 06:45:34 -0400 Message-ID: <20221012104534.826549315@goodmis.org> User-Agent: quilt/0.66 Date: Wed, 12 Oct 2022 06:40:58 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Andrew Morton , Tom Zanussi , stable@vger.kernel.org Subject: [PATCH v2 3/3] tracing: Fix reading strings from synthetic events References: <20221012104055.421393330@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Steven Rostedt (Google)" The follow commands caused a crash: # cd /sys/kernel/tracing # echo 's:open char file[]' > dynamic_events # echo 'hist:keys=3Dcommon_pid:file=3Dfilename:onchange($file).trace(open= ,$file)' > events/syscalls/sys_enter_openat/trigger' # echo 1 > events/synthetic/open/enable BOOM! The problem is that the synthetic event field "char file[]" will read the value given to it as a string without any memory checks to make sure the address is valid. The above example will pass in the user space address and the sythetic event code will happily call strlen() on it and then strscpy() where either one will cause an oops when accessing user space addresses. Use the helper functions from trace_kprobe and trace_eprobe that can read strings safely (and actually succeed when the address is from user space and the memory is mapped in). Now the above can show: packagekitd-1721 [000] ...2. 104.597170: open: file=3D/usr/lib/rp= m/fileattrs/cmake.attr in:imjournal-978 [006] ...2. 104.599642: open: file=3D/var/lib/rs= yslog/imjournal.state.tmp packagekitd-1721 [000] ...2. 104.626308: open: file=3D/usr/lib/rp= m/fileattrs/debuginfo.attr Cc: stable@vger.kernel.org Fixes: bd82631d7ccdc ("tracing: Add support for dynamic strings to syntheti= c events") Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace_events_synth.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_= synth.c index 5e8c07aef071..e310052dc83c 100644 --- a/kernel/trace/trace_events_synth.c +++ b/kernel/trace/trace_events_synth.c @@ -17,6 +17,8 @@ /* for gfp flag names */ #include #include +#include "trace_probe.h" +#include "trace_probe_kernel.h" =20 #include "trace_synth.h" =20 @@ -409,6 +411,7 @@ static unsigned int trace_string(struct synth_trace_eve= nt *entry, { unsigned int len =3D 0; char *str_field; + int ret; =20 if (is_dynamic) { u32 data_offset; @@ -417,19 +420,27 @@ static unsigned int trace_string(struct synth_trace_e= vent *entry, data_offset +=3D event->n_u64 * sizeof(u64); data_offset +=3D data_size; =20 - str_field =3D (char *)entry + data_offset; - - len =3D strlen(str_val) + 1; - strscpy(str_field, str_val, len); + len =3D kern_fetch_store_strlen((unsigned long)str_val); =20 data_offset |=3D len << 16; *(u32 *)&entry->fields[*n_u64] =3D data_offset; =20 + ret =3D kern_fetch_store_string((unsigned long)str_val, &entry->fields[*= n_u64], entry); + (*n_u64)++; } else { str_field =3D (char *)&entry->fields[*n_u64]; =20 - strscpy(str_field, str_val, STR_VAR_LEN_MAX); +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE + if ((unsigned long)str_val < TASK_SIZE) + ret =3D strncpy_from_user_nofault(str_field, str_val, STR_VAR_LEN_MAX); + else +#endif + ret =3D strncpy_from_kernel_nofault(str_field, str_val, STR_VAR_LEN_MAX= ); + + if (ret < 0) + strcpy(str_field, FAULT_STRING); + (*n_u64) +=3D STR_VAR_LEN_MAX / sizeof(u64); } =20 @@ -462,7 +473,7 @@ static notrace void trace_event_raw_event_synth(void *_= _data, val_idx =3D var_ref_idx[field_pos]; str_val =3D (char *)(long)var_ref_vals[val_idx]; =20 - len =3D strlen(str_val) + 1; + len =3D kern_fetch_store_strlen((unsigned long)str_val); =20 fields_size +=3D len; } --=20 2.35.1