FAILED: patch "[PATCH] tracing: Take trace_array reference when opening options file" failed to apply to 6.18-stable tree

PATCH New [email protected] 2 participants 4 messages Sep 8 – Sep 10

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Stable branch Tracing

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lore

[email protected]

author maintainer

2026-09-08 13:14 UTC #0 lore raw

The patch below does not apply to the 6.18-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 <[email protected]>.

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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x f2951ebd15c36a1ea4820a7f0cbb0b5f1c028b73
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090831-flashback-racing-7323@gregkh' --subject-prefix 'PATCH 6.18.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 <[email protected]>
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 [email protected]

Link https://patch.msgid.link/[email protected] open here

Fixes 577b785f55168 ("tracing: add tracer dependent options to options directory")

Reported-by [email protected]

Closes https://lore.kernel.org/linux-trace-kernel/[email protected]/ open here

Signed-off-by Steven Rostedt <[email protected]>

kernel/trace/trace.c +63 -4

index a946e0183fd1..722d0ba2d233 100644
@@ -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,

Sasha Levin

maintainer

2026-09-10 12:53 UTC #1 lore raw

PATCH 1/3 tracing: Clean up use of trace_create_maxlat_file()

From: Steven Rostedt <[email protected]>

[ Upstream commit ba73713da50e5c24499ca8941171593466ea34f7 ]

In trace.c, the function trace_create_maxlat_file() is defined behind the
#ifdef CONFIG_TRACER_MAX_TRACE block. The #else part defines it as:

 #define trace_create_maxlat_file(tr, d_tracer)				\
	trace_create_file("tracing_max_latency", TRACE_MODE_WRITE,	\
			  d_tracer, tr, &tracing_max_lat_fops)

But the one place that it it used has:

 #ifdef CONFIG_TRACER_MAX_TRACE
	trace_create_maxlat_file(tr, d_tracer);

#endif

Which is pointless and also wrong!

It only gets created when both CONFIG_TRACE_MAX_TRACE and CONFIG_FS_NOTIFY is defined, but the file itself should not be dependent on CONFIG_FS_NOTIFY. Always create that file when TRACE_MAX_TRACE is defined regardless if FS_NOTIFY is or is not.

Cc Mathieu Desnoyers <[email protected]>

Acked-by Masami Hiramatsu (Google) <[email protected]>

Link https://patch.msgid.link/20260207191101.0e014abd@robin open here

Signed-off-by Steven Rostedt (Google) <[email protected]>

Stable-dep-of: f2951ebd15c3 ("tracing: Take trace_array reference when opening options file")

Signed-off-by Sasha Levin <[email protected]>

---
 kernel/trace/trace.c | 38 ++++++++++++++++----------------------
 1 file changed, 16 insertions(+), 22 deletions(-)

kernel/trace/trace.c +16 ~~-22~~

index e62772a76671e..675602fd9a41a 100644
@@ -1904,10 +1904,7 @@ static ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt)
 unsigned long __read_mostly	tracing_thresh;
 
 #ifdef CONFIG_TRACER_MAX_TRACE
-static const struct file_operations tracing_max_lat_fops;
-
 #ifdef LATENCY_FS_NOTIFY
-
 static struct workqueue_struct *fsnotify_wq;
 
 static void latency_fsnotify_workfn(struct work_struct *work)

@@ -1924,17 +1921,6 @@ static void latency_fsnotify_workfn_irq(struct irq_work *iwork)
 	queue_work(fsnotify_wq, &tr->fsnotify_work);
 }
 
-static void trace_create_maxlat_file(struct trace_array *tr,
-				     struct dentry *d_tracer)
-{
-	INIT_WORK(&tr->fsnotify_work, latency_fsnotify_workfn);
-	init_irq_work(&tr->fsnotify_irqwork, latency_fsnotify_workfn_irq);
-	tr->d_max_latency = trace_create_file("tracing_max_latency",
-					      TRACE_MODE_WRITE,
-					      d_tracer, tr,
-					      &tracing_max_lat_fops);
-}
-
 __init static int latency_fsnotify_init(void)
 {
 	fsnotify_wq = alloc_workqueue("tr_max_lat_wq",

@@ -1959,14 +1945,22 @@ void latency_fsnotify(struct trace_array *tr)
 	 */
 	irq_work_queue(&tr->fsnotify_irqwork);
 }
+#endif /* !LATENCY_FS_NOTIFY */
 
-#else /* !LATENCY_FS_NOTIFY */
-
-#define trace_create_maxlat_file(tr, d_tracer)				\
-	trace_create_file("tracing_max_latency", TRACE_MODE_WRITE,	\
-			  d_tracer, tr, &tracing_max_lat_fops)
+static const struct file_operations tracing_max_lat_fops;
 
+static void trace_create_maxlat_file(struct trace_array *tr,
+				     struct dentry *d_tracer)
+{
+#ifdef LATENCY_FS_NOTIFY
+	INIT_WORK(&tr->fsnotify_work, latency_fsnotify_workfn);
+	init_irq_work(&tr->fsnotify_irqwork, latency_fsnotify_workfn_irq);
 #endif
+	tr->d_max_latency = trace_create_file("tracing_max_latency",
+					      TRACE_MODE_WRITE,
+					      d_tracer, tr,
+					      &tracing_max_lat_fops);
+}
 
 /*
  * Copy the new maximum trace into the separate maximum-trace

@@ -2101,7 +2095,9 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
 	__update_max_tr(tr, tsk, cpu);
 	arch_spin_unlock(&tr->max_lock);
 }
-
+#else /* !CONFIG_TRACER_MAX_TRACE */
+static inline void trace_create_maxlat_file(struct trace_array *tr,
+					    struct dentry *d_tracer) { }
 #endif /* CONFIG_TRACER_MAX_TRACE */
 
 struct pipe_wait {

@@ -10392,9 +10388,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
 
 	create_trace_options_dir(tr);
 
-#ifdef CONFIG_TRACER_MAX_TRACE
 	trace_create_maxlat_file(tr, d_tracer);
-#endif
 
 	if (ftrace_create_function_files(tr, d_tracer))
 		MEM_FAIL(1, "Could not allocate function filter files");

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-10 12:53 UTC #2 lore raw

PATCH 2/3 tracing: Make printk_trace global for tracing system

From: Steven Rostedt <[email protected]>

[ Upstream commit 1c53d781d42541adc5ba76b4f843a3ff382e01fb ]

The printk_trace is used to determine which trace_array trace_printk() writes to. By making it a global variable among the tracing subsystem it will allow the trace_printk functions to be moved out of trace.c and still have direct access to that variable.

Cc Masami Hiramatsu <[email protected]>

Cc Mark Rutland <[email protected]>

Cc Mathieu Desnoyers <[email protected]>

Cc Andrew Morton <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Steven Rostedt (Google) <[email protected]>

Stable-dep-of: f2951ebd15c3 ("tracing: Take trace_array reference when opening options file")

Signed-off-by Sasha Levin <[email protected]>

---
 kernel/trace/trace.c | 2 +-
 kernel/trace/trace.h | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

kernel/trace/trace.c +1 -1

index 675602fd9a41a..063e88fbe3856 100644
@@ -537,7 +537,7 @@ static struct trace_array global_trace = {
 	.trace_flags = TRACE_DEFAULT_FLAGS,
 };
 
-static struct trace_array *printk_trace = &global_trace;
+struct trace_array *printk_trace = &global_trace;
 
 /* List of trace_arrays interested in the top level trace_marker */
 static LIST_HEAD(marker_copies);

kernel/trace/trace.h +2 -0

index 62d5a5f224c4a..cea39bbcf52f0 100644
@@ -479,6 +479,8 @@ extern bool trace_clock_in_ns(struct trace_array *tr);
 
 extern unsigned long trace_adjust_address(struct trace_array *tr, unsigned long addr);
 
+extern struct trace_array *printk_trace;
+
 /*
  * The global tracer (top) should be the first trace array added,
  * but we check the flag anyway.

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-10 12:53 UTC #3 lore raw

PATCH 3/3 tracing: Take trace_array reference when opening options file

In reply to Sasha Levin

From: Steven Rostedt <[email protected]>

[ Upstream commit f2951ebd15c36a1ea4820a7f0cbb0b5f1c028b73 ]

Cc [email protected]

Link https://patch.msgid.link/[email protected] open here

Fixes 577b785f55168 ("tracing: add tracer dependent options to options directory")

Reported-by [email protected]

Closes https://lore.kernel.org/linux-trace-kernel/[email protected]/ open here

Signed-off-by Steven Rostedt <[email protected]>

[ replaced the unavailable __trace_array_get(tr) call with tr->ref++ and return 0. ]

Signed-off-by Sasha Levin <[email protected]>

---
 kernel/trace/trace.c | 69 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 65 insertions(+), 4 deletions(-)

kernel/trace/trace.c +65 -4

index 063e88fbe3856..8c8a2aad3e49b 100644
@@ -9393,11 +9393,72 @@ 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]) {
+			tr->ref++;
+			return 0;
+		}
+	}
+	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,

Signature · 1 line

2.53.0