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* FAILED: patch "[PATCH] tracing: Take trace_array reference when opening a tracer" failed to apply to 5.15-stable tree
@ 2026-09-16 11:26 gregkh
  2026-09-16 20:00 ` [PATCH 5.15.y 1/2] tracing: Clean up use of trace_create_maxlat_file() Sasha Levin
  0 siblings, 1 reply; 4+ messages in thread
From: gregkh @ 2026-09-16 11:26 UTC (permalink / raw)
  To: rostedt; +Cc: stable


The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x ed0aff60f83a9bdc2f6556376ac79c96b3ce7e80
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026091636-refined-everyone-e63c@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ed0aff60f83a9bdc2f6556376ac79c96b3ce7e80 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <rostedt@goodmis.org>
Date: Thu, 10 Sep 2026 22:12:09 -0400
Subject: [PATCH] tracing: Take trace_array reference when opening a tracer
 options file

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 <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8658cad53cb5..e4a490d3d08c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7717,12 +7717,55 @@ 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))
+			return __trace_array_get(tr);
+	}
+	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;
 
@@ -7984,6 +8027,7 @@ 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 5e76f94e7a80..bd3c8f80300f 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -227,6 +227,7 @@ 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);


^ permalink raw reply related	[flat|nested] 4+ messages in thread
* FAILED: patch "[PATCH] tracing: Take trace_array reference when opening options file" failed to apply to 5.15-stable tree
@ 2026-09-08 12:56 gregkh
  2026-09-10 15:11 ` [PATCH 5.15.y 1/2] tracing: Clean up use of trace_create_maxlat_file() Sasha Levin
  0 siblings, 1 reply; 4+ messages in thread
From: gregkh @ 2026-09-08 12:56 UTC (permalink / raw)
  To: rostedt; +Cc: stable


The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x f2951ebd15c36a1ea4820a7f0cbb0b5f1c028b73
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090833-imaging-carving-723a@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f2951ebd15c36a1ea4820a7f0cbb0b5f1c028b73 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <rostedt@goodmis.org>
Date: Wed, 2 Sep 2026 12:19:18 -0400
Subject: [PATCH] tracing: Take trace_array reference when opening options file

The options files do not take the trace_array reference for the options
they represent. This could cause a use-after-free kernel crash if one of
these files is opened by one task and another task removes the instance
that the option is for. Because it doesn't take a reference upon opening,
it will not stop the removal which will free the options descriptor that
is being used.

As the options are somewhat dynamic in their creation at boot up, each
file represents a flag in the trace_array. The trace_array has an array of
indexes to represent each of these flags that is stored in the
trace_flags_index array. The address of the index array element is used to
pass to the inode->i_private pointer. Then that element is read which
holds the index (which represents the flag) and then the index is used to
calculate the trace_array descriptor from its trace_flags_index array.

One issue is that the index element can not be referenced until the
trace_array's reference is taken. To handle this, create a new helper
function called: trace_array_options_get() that will iterate all the
existing trace_arrays in the ftrace_trace_arrays list (under the
trace_types_lock), and compare the passed in address of the index element
with the entire array of the trace_array's trace_flags_index array.
If it matches, then up the corresponding trace_array's reference and
return.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902121918.5a9e9d1b@gandalf.local.home
Fixes: 577b785f55168 ("tracing: add tracer dependent options to options directory")
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/linux-trace-kernel/20260828135858.2AC501F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a946e0183fd1..722d0ba2d233 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7842,11 +7842,70 @@ trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	return cnt;
 }
 
+/*
+ * The tr_index is the address of a trace_array->trace_flags_index[]
+ * element that holds the index of the trace flag. But since the
+ * trace_array reference has not been taken yet, it cannot be referenced
+ * 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 tr_index to the
+ * address of the entire trace_array trace_flags_index 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_options_get(void *tr_index)
+{
+	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_index >= (void *)&tr->trace_flags_index[0] &&
+		    tr_index < (void *)&tr->trace_flags_index[TRACE_FLAGS_MAX_SIZE])
+			return __trace_array_get(tr);
+	}
+	return -ENODEV;
+}
+
+static int trace_options_open(struct inode *inode, struct file *filp)
+{
+	void *tr_index = inode->i_private;
+
+	if (trace_array_options_get(tr_index) < 0)
+		return -ENODEV;
+
+	filp->private_data = tr_index;
+
+	return 0;
+}
+
+static int trace_options_release(struct inode *inode, struct file *filp)
+{
+	void *tr_index = filp->private_data;
+	struct trace_array *tr;
+	unsigned int index;
+
+	get_tr_index(tr_index, &tr, &index);
+
+	trace_array_put(tr);
+
+	return 0;
+}
+
 static const struct file_operations trace_options_core_fops = {
-	.open = tracing_open_generic,
-	.read = trace_options_core_read,
-	.write = trace_options_core_write,
-	.llseek = generic_file_llseek,
+	.open		= trace_options_open,
+	.read		= trace_options_core_read,
+	.write		= trace_options_core_write,
+	.llseek		= generic_file_llseek,
+	.release	= trace_options_release,
 };
 
 struct dentry *trace_create_file(const char *name,


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2026-09-16 11:26 FAILED: patch "[PATCH] tracing: Take trace_array reference when opening a tracer" failed to apply to 5.15-stable tree gregkh
2026-09-16 20:00 ` [PATCH 5.15.y 1/2] tracing: Clean up use of trace_create_maxlat_file() Sasha Levin
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2026-09-10 15:11 ` [PATCH 5.15.y 1/2] tracing: Clean up use of trace_create_maxlat_file() Sasha Levin

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