From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 383393D5C06; Tue, 13 Oct 2026 12:24:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791894271; cv=none; b=ZYfjr4kEn6XUZ+wWOFoKZ8FRWf+DREsEqaxXPWdgqZAVN5Ov/Egyol/Yg/IuNZBYLcDAq3FUiuDRGnjloOmHhWGvZri9egp6dTKwXXST6/nptajpqG4uNaU0oXf926glPiLDuz7si1QQ3GPTiSsnGJCF7lyuWMERpUOh4QjA4gQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791894271; c=relaxed/simple; bh=RMiYIvbmURnkw0HyRJNkLZeFnIwril2F1qpOcsxI1xU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=M76X8xo+mEhPhgLpUD2qVkwY4HgYTfVjoh3zFMAv0Erd00aNnGj6iTROzo+VuPEnS35xChdQPM1gMX7ddcEmZeAddhXvvLLrUPeABppHkJ86N7VDyrTbD8D/kImWI/1CF+yOAZrbKYXo65LulnpRcUq00KGaWVR4vpi5mTWJBXg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Ufr420hf; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Ufr420hf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8CFA31F000FF; Tue, 13 Oct 2026 12:24:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791894270; bh=X1kDgAOON/rtX2vbQwF/8unL1Z+AKN2mtc1p3MAyTa4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Ufr420hfiDlmrf+8I220JW1S43kdBN2XWeKcPrrsz5lr7op17bkjXhRfQzDWzu7Nu V36uqGea8BqJrYsX3a6lnh8K1rgl0ZOWha9b7u08bjIEreuQ9bUyscVOE2rJ7qmZ2h zW8egHk7Q0kTV3i7NH7UvNh4W+5waBcRX6v069rQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, sashiko-bot@kernel.org, Steven Rostedt , Sasha Levin Subject: [PATCH 6.18 504/621] tracing: Take trace_array reference when opening a tracer options file Date: Tue, 13 Oct 2026 13:38:19 +0200 Message-ID: <20261013112932.787265651@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112920.855194808@linuxfoundation.org> References: <20261013112920.855194808@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Steven Rostedt [ Upstream commit ed0aff60f83a9bdc2f6556376ac79c96b3ce7e80 ] When a tracer option file is opened, it is passed a descriptor that points to an element on the trace_array's topts array. This element has information to find the trace array and other information. It uses this element to take a reference of the trace_array so that the trace_array does not get removed while this file is opened. Unfortunately, there's a race condition where the element itself could be freed by the removal of the instance the trace_array represents causing a use-after-free as this element that is used to find the trace_array to increment its reference counter is also freed when the instance is removed. To solve this, add a trace_array_tracer_options_get() helper function that will take the address of the element that is passed to the open function by the inode->i_private pointer and search all the trace_arrays under a lock to find the one that the element's address is in the range of the trace_arrays topts array elements. When a match happens, that trace_array's reference would be increased. Note, there's a race where if an admin was deleting and creating trace instances at the same time and the memory of the old trace_array's array matched the memory of the new trace_array that it could in theory open the option from the wrong trace array. But we do not care because it would be stupid to perform that kind of action. As long as the only thing that can happen is that the option from the wrong trace array is used and doesn't crash the kernel it will only make the user confused. But if they are doing something stupid like this, they are already confused, so no harm done. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260910221209.62dad8d3@robin Fixes: 7e2cfbd2d3c86 ("tracing: Have option files inc the trace array ref count") Reported-by: sashiko-bot@kernel.org Closes: https://lore.kernel.org/linux-trace-kernel/20260902121918.5a9e9d1b@gandalf.local.home/ Signed-off-by: Steven Rostedt Signed-off-by: Sasha Levin --- kernel/trace/trace.c | 48 +++++++++++++++++++++++++++++++++++++++++++- kernel/trace/trace.h | 1 + 2 files changed, 48 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 7f25ae6330942..0c0f31e63d05d 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -9279,12 +9279,57 @@ trace_options_write(struct file *filp, const char __user *ubuf, size_t cnt, return cnt; } +static bool tr_option_match(struct trace_array *tr, void *topt) +{ + for (int i = 0; i < tr->nr_topts; i++) { + struct trace_options *tr_topts = &tr->topts[i]; + + if (topt >= (void *)&tr_topts->topts[0] && + topt < (void *)&tr_topts->topts[tr_topts->nr_topts]) + return true; + } + return false; +} + +/* + * The topt is the address of a trace_array->topts[] element that holds the + * the tracer options descriptor. But since the trace_array reference has not + * been taken yet, it cannot be dereferenced as it could have been freed by + * a rmdir of the instance the trace_array represents. + * + * Search the list of trace_arrays and compare the topt to the address of + * the entire trace_array topts array for each trace_array in the list. + * If one is matched, then take the reference and return it. If not, the + * trace_array no longer exits. + */ +static int trace_array_tracer_options_get(void *topt) +{ + struct trace_array *tr; + int ret; + + ret = security_locked_down(LOCKDOWN_TRACEFS); + if (ret) + return ret; + + if (tracing_disabled) + return -ENODEV; + + guard(mutex)(&trace_types_lock); + list_for_each_entry(tr, &ftrace_trace_arrays, list) { + if (tr_option_match(tr, topt)) { + tr->ref++; + return 0; + } + } + return -ENODEV; +} + static int tracing_open_options(struct inode *inode, struct file *filp) { struct trace_option_dentry *topt = inode->i_private; int ret; - ret = tracing_check_open_get_tr(topt->tr); + ret = trace_array_tracer_options_get(topt); if (ret) return ret; @@ -9568,6 +9613,7 @@ create_trace_option_files(struct trace_array *tr, struct tracer *tracer) tr->topts = tr_topts; tr->topts[tr->nr_topts].tracer = tracer; tr->topts[tr->nr_topts].topts = topts; + tr->topts[tr->nr_topts].nr_topts = cnt; tr->nr_topts++; for (cnt = 0; opts[cnt].name; cnt++) { diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index ab88b87ac2ee2..39c425a9538a5 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -224,6 +224,7 @@ struct array_buffer { struct trace_options { struct tracer *tracer; struct trace_option_dentry *topts; + int nr_topts; }; struct trace_pid_list *trace_pid_list_alloc(void); -- 2.53.0