From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2845125B08D for ; Fri, 28 Aug 2026 16:33:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787934829; cv=none; b=iVDRpNiLrGiOWS+ZvtTGNEvnkuTSL0PAJJ4mNV8IQBlHWySWsdRX3zxq2ICF8sEX1o8uwIY+rRTQQMa/uLuUe7IB4HfsGj7HQsxzS3psoJ411s1y7WAasfBI+8F/2PKxvUlyoPJKFRTlFeIod8zWs2jOCqfiGCm84hgTg5A2sT4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787934829; c=relaxed/simple; bh=9HSRueymnHQnumlP71WqP6C9CeR414LuTtFYONZ46K0=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=MEqy3YWUdy2tCjymxYC8wS1IX3cEbx8ImgIVgGk7zFW6ZVjjL51/mtYo9Uokk0roK/O5/h/1Lcl2eUBtiS/DNazQ8Udb9nAGjIyRE3EQGHrwMeBwoQtvZksJD8+JVWDz8Sz/3AmNWkMaurfdu8WPYupXIICThxR7I3ODGRmwqEE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.b=5KmBiQoY; arc=none smtp.client-ip=216.40.44.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.b="5KmBiQoY" Received: from omf02.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id BFBFFC046C; Fri, 28 Aug 2026 16:33:42 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf02.hostedemail.com (Postfix) with ESMTPA id 1215F80012; Fri, 28 Aug 2026 16:33:40 +0000 (UTC) Date: Fri, 28 Aug 2026 12:34:30 -0400 From: Steven Rostedt To: Breno Leitao Cc: mark.rutland@arm.com, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: ftrace: UAF in ftrace_regex_open() on a removed tracing instance Message-ID: <20260828123430.22d43b44@gandalf.local.home> In-Reply-To: References: <20260828104201.21aa9d08@gandalf.local.home> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 1215F80012 X-Stat-Signature: dd9yjheigdjgcxoa7cs94h7ksem8fjfc X-Rspamd-Server: rspamout07 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX19ilEJ0sPgTXV3zdQZWVvo4cNFXGrg1yaA= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=3a4s3Zj8VMrkmsYP6OiMSzG3EOe0UYRfujTzuOKdAqQ=; b=5KmBiQoY3pJc0pcJFD45K/fmT+ApIneFQLVrtoyT1w9+bGsOt4C9ZiQzchsKyHLzIZyKGMbPaFb3PmBMCHMcal+ll3NeWQuJi81oZEaliimpz6ZFjHASmRt4dfr675h7Li7vMB/pxzHQTI5bMB+uXRN0a/GQmkjLZuh1M/Aubf0= X-HE-Tag: 1787934820-738212 X-HE-Meta: U2FsdGVkX1/C1JSNPQeNeDT8DPFkgEjw6mP66+v/BcrHZVwL+eM+nvKAm6cckN88Icn/tjq1FeABat3gzQXvQWL0vSXayNmnzibAV4N0arBt3x8vzGifZErrg/Zzv9lUcSvickEx5gaN7JQZ7KNXKjildNRLuY9AEFzJmv7CPHM5h/D1VNHf49QE3qJYh255mTvBvwYuvntoxjZRpwJF2rlNXzFIqo2fP5r+qDNtKef55lOMg5iMCkJLIEdXi/ZEs0LkuW86uHGF9PT2ZCsycB1yxNUv4p7BZPj9y2qUfGNMDCkLYUDymI9SwIpPy9+/ltLxWlmoH1+jbytIRoJtEHIndn+mif// On Fri, 28 Aug 2026 08:59:39 -0700 Breno Leitao wrote: > > My LLM came up with something like the following, and it doesn't > reproduce the problem anymore. Very similar to your code above: I know the solution but there's subtle things I want to make sure that works. > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index f9d80c7bd9f16..37845399fe5cf 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -4788,22 +4788,37 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag, > static int > ftrace_filter_open(struct inode *inode, struct file *file) > { > - struct ftrace_ops *ops = inode->i_private; > + struct trace_array *tr = inode->i_private; > + int ret; > > - /* Checks for tracefs lockdown */ > - return ftrace_regex_open(ops, > - FTRACE_ITER_FILTER | FTRACE_ITER_DO_PROBES, > - inode, file); > + /* Checks for tracefs lockdown, and that the instance is still alive */ > + ret = tracing_check_open_get_tr(tr); > + if (ret) > + return ret; > + > + ret = ftrace_regex_open(tr->ops, > + FTRACE_ITER_FILTER | FTRACE_ITER_DO_PROBES, > + inode, file); > + /* ftrace_regex_open() holds its own reference on success */ > + trace_array_put(tr); > + return ret; > } > > static int > ftrace_notrace_open(struct inode *inode, struct file *file) > { > - struct ftrace_ops *ops = inode->i_private; > + struct trace_array *tr = inode->i_private; > + int ret; > + > + /* Checks for tracefs lockdown, and that the instance is still alive */ > + ret = tracing_check_open_get_tr(tr); > + if (ret) > + return ret; > > - /* Checks for tracefs lockdown */ > - return ftrace_regex_open(ops, FTRACE_ITER_NOTRACE, > - inode, file); > + ret = ftrace_regex_open(tr->ops, FTRACE_ITER_NOTRACE, inode, file); > + /* ftrace_regex_open() holds its own reference on success */ > + trace_array_put(tr); > + return ret; > } > > /* Type for quick search ftrace basic regexes (globs) from filter_parse_regex */ > @@ -7496,11 +7511,15 @@ void ftrace_create_filter_files(struct ftrace_ops *ops, > struct dentry *parent) > { > > + /* > + * Pass the trace array and not @ops, as @ops is freed when the > + * instance is removed, but the trace array can still be validated. > + */ I hate these comments. It's really pointless to state this. It's a "no shit" comment ;-) > trace_create_file("set_ftrace_filter", TRACE_MODE_WRITE, parent, > - ops, &ftrace_filter_fops); > + ops->private, &ftrace_filter_fops); But this also assumes that ops->private is always a trace_array. Which may someday change and we will get a hidden bug if it does. -- Steve > > trace_create_file("set_ftrace_notrace", TRACE_MODE_WRITE, parent, > - ops, &ftrace_notrace_fops); > + ops->private, &ftrace_notrace_fops); > } > > /* From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 526AD346A14 for ; Fri, 28 Aug 2026 16:34:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.12 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787934848; cv=none; b=jJu0biyfNTSXi6v6Fjipex4mnWFQOM/ykaM8HvmkHcQFF3vFsWCnohvMOuWAAv1w0zWpl0mW5HHs9IYzLjNSCcgVe3Yv6IBxVQ+tg/Imb+eX0Qsu44Syo0fvGJa/NiKnb5CfeKirVjPv/BC0+1Qgi0f0cP+H5JC7MwNJ9OBmBoc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787934848; c=relaxed/simple; bh=SMBK2Yy7EbjA2SEaIooljoEXmFpi0vgTfw4WNzbXxM8=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=YRlyeEfdd8y3IMAej9wQc73MjPVxHUIMAmXfkgiZnPZIaNyj1HiiRCaigw2RdabcdKRJ7cI/incc4jJ5lrZg2N2U1ZaN18RgbAJyjhc33OCwTGaqx7v7xOeDK6Pse36DH1iB2g2wp7e0MAvyP9J1Uzyksgr5xRoaPGEw7+cLLkc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.b=onZ96OnV; arc=none smtp.client-ip=216.40.44.12 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.b="onZ96OnV" Received: from omf08.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 5EF30A0477; Fri, 28 Aug 2026 16:34:04 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf08.hostedemail.com (Postfix) with ESMTPA id B4D1720027; Fri, 28 Aug 2026 16:34:02 +0000 (UTC) Date: Fri, 28 Aug 2026 12:34:52 -0400 From: Steven Rostedt To: Breno Leitao Cc: mark.rutland@arm.com, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: ftrace: UAF in ftrace_regex_open() on a removed tracing instance Message-ID: <20260828123430.22d43b44@gandalf.local.home> In-Reply-To: References: <20260828104201.21aa9d08@gandalf.local.home> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 5yi85nyoky7kbqynbo4y16nzwkw185oi X-Rspamd-Server: rspamout08 X-Rspamd-Queue-Id: B4D1720027 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1+D+plsFRN12ivv4iCA5vfIigbWuXeHlsQ= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=VUWdWiE20cmNutD4YDHUMmXMGw9dsti+jXOrsvFJPwk=; b=onZ96OnVa+Wcrm50/yBkJtbu955pWQ2k0ou2ciTtd679XPdLUlm0cQnOwJxqyydePcAT0kU7+tMyGHAOLbbKbfqpI94IxBrqtPjGwKXKSmfqdEB/RJe/7zogImgn85g3PQ5//UdsuC9JsC+Eyu5PSphcZN3FasNWfkI7+qUzYkQ= X-HE-Tag: 1787934842-838244 X-HE-Meta: U2FsdGVkX18xNdSOMMjpAy+Gc4O7vwkHvNidlHSx7URjm5N2GatyaFBEcMqwmJo1ICiMCpNMpC2tjpGYcKrbv7NJhjeSQhvUVQEA1cCcrtgdX/0gkSRMhmxdlzOBZ4Cm7ruP2OvhJs08eXLwJ3DXsiNh6LW7sW88mB5V9d6OkCwElUxRQ/4O7dBoFghatrVhh7gPAzQYxyWBwHYI3biBQXNeFKjrzZ/cvLE5mksy38bCz/jqBuqYgWzo2xx0c2c2zprmRAlm6JkWMdRh8nqPE4/zs7zdScTeMPe8HJ4X3drtcVJzSosKf0iusO9wUBMYkRwWqC6uozrAXaj7HVCswmPYAusVjRM7 Message-ID: <20260828163452.FSU7ejbJe9onK4amKMjmoCOJqemfXwQZjCrHsdy33eY@z> On Fri, 28 Aug 2026 08:59:39 -0700 Breno Leitao wrote: > > My LLM came up with something like the following, and it doesn't > reproduce the problem anymore. Very similar to your code above: I know the solution but there's subtle things I want to make sure that works. > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index f9d80c7bd9f16..37845399fe5cf 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -4788,22 +4788,37 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag, > static int > ftrace_filter_open(struct inode *inode, struct file *file) > { > - struct ftrace_ops *ops = inode->i_private; > + struct trace_array *tr = inode->i_private; > + int ret; > > - /* Checks for tracefs lockdown */ > - return ftrace_regex_open(ops, > - FTRACE_ITER_FILTER | FTRACE_ITER_DO_PROBES, > - inode, file); > + /* Checks for tracefs lockdown, and that the instance is still alive */ > + ret = tracing_check_open_get_tr(tr); > + if (ret) > + return ret; > + > + ret = ftrace_regex_open(tr->ops, > + FTRACE_ITER_FILTER | FTRACE_ITER_DO_PROBES, > + inode, file); > + /* ftrace_regex_open() holds its own reference on success */ > + trace_array_put(tr); > + return ret; > } > > static int > ftrace_notrace_open(struct inode *inode, struct file *file) > { > - struct ftrace_ops *ops = inode->i_private; > + struct trace_array *tr = inode->i_private; > + int ret; > + > + /* Checks for tracefs lockdown, and that the instance is still alive */ > + ret = tracing_check_open_get_tr(tr); > + if (ret) > + return ret; > > - /* Checks for tracefs lockdown */ > - return ftrace_regex_open(ops, FTRACE_ITER_NOTRACE, > - inode, file); > + ret = ftrace_regex_open(tr->ops, FTRACE_ITER_NOTRACE, inode, file); > + /* ftrace_regex_open() holds its own reference on success */ > + trace_array_put(tr); > + return ret; > } > > /* Type for quick search ftrace basic regexes (globs) from filter_parse_regex */ > @@ -7496,11 +7511,15 @@ void ftrace_create_filter_files(struct ftrace_ops *ops, > struct dentry *parent) > { > > + /* > + * Pass the trace array and not @ops, as @ops is freed when the > + * instance is removed, but the trace array can still be validated. > + */ I hate these comments. It's really pointless to state this. It's a "no shit" comment ;-) > trace_create_file("set_ftrace_filter", TRACE_MODE_WRITE, parent, > - ops, &ftrace_filter_fops); > + ops->private, &ftrace_filter_fops); But this also assumes that ops->private is always a trace_array. Which may someday change and we will get a hidden bug if it does. This is the exact reason I want to look deeper at it. -- Steve > > trace_create_file("set_ftrace_notrace", TRACE_MODE_WRITE, parent, > - ops, &ftrace_notrace_fops); > + ops->private, &ftrace_notrace_fops); > } > > /*