[PATCH v4 1/2] tracing: Return ERR_PTR() from expr_str()

[PATCH v4 1/2] tracing: Return ERR_PTR() from expr_str()

[Pengpeng Hou]

expr_str() already has failure cases for invalid recursion depth and
allocation failure, but it currently reports them as a bare NULL. Teach
it to return ERR_PTR()-encoded errors and update parse_unary() and
parse_expr() to propagate those errors.

This keeps the error conversion separate from the string-building change
so the follow-up seq_buf patch can stay focused on the overflow fix
itself.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
Changes since v3: https://lore.kernel.org/all/20260417223002.2-tracing-expr-v3-pengpeng@iscas.ac.cn/
- split the ERR_PTR() conversion into a separate patch as requested by
  Steven
- use __free(kfree) and return_ptr() in expr_str()
- propagate ERR_PTR() errors from parse_unary() and parse_expr()

 kernel/trace/trace_events_hist.c | 37 +++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 0dbbf6cca9bc..0b33bb8ef6f7 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1769,18 +1769,18 @@ static void expr_field_str(struct hist_field *field, char *expr)
 
 static char *expr_str(struct hist_field *field, unsigned int level)
 {
-	char *expr;
+	char *expr __free(kfree) = NULL;
 
 	if (level > 1)
-		return NULL;
+		return ERR_PTR(-EINVAL);
 
 	expr = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
 	if (!expr)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	if (!field->operands[0]) {
 		expr_field_str(field, expr);
-		return expr;
+		return_ptr(expr);
 	}
 
 	if (field->operator == FIELD_OP_UNARY_MINUS) {
@@ -1788,16 +1788,15 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 
 		strcat(expr, "-(");
 		subexpr = expr_str(field->operands[0], ++level);
-		if (!subexpr) {
-			kfree(expr);
-			return NULL;
-		}
+		if (IS_ERR(subexpr))
+			return subexpr;
+
 		strcat(expr, subexpr);
 		strcat(expr, ")");
 
 		kfree(subexpr);
 
-		return expr;
+		return_ptr(expr);
 	}
 
 	expr_field_str(field->operands[0], expr);
@@ -1816,13 +1815,12 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 		strcat(expr, "*");
 		break;
 	default:
-		kfree(expr);
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	expr_field_str(field->operands[1], expr);
 
-	return expr;
+	return_ptr(expr);
 }
 
 /*
@@ -2636,6 +2634,11 @@ static struct hist_field *parse_unary(struct hist_trigger_data *hist_data,
 	expr->is_signed = operand1->is_signed;
 	expr->operator = FIELD_OP_UNARY_MINUS;
 	expr->name = expr_str(expr, 0);
+	if (IS_ERR(expr->name)) {
+		ret = PTR_ERR(expr->name);
+		expr->name = NULL;
+		goto free;
+	}
 	expr->type = kstrdup_const(operand1->type, GFP_KERNEL);
 	if (!expr->type) {
 		ret = -ENOMEM;
@@ -2848,6 +2851,11 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		destroy_hist_field(operand1, 0);
 
 		expr->name = expr_str(expr, 0);
+		if (IS_ERR(expr->name)) {
+			ret = PTR_ERR(expr->name);
+			expr->name = NULL;
+			goto free_expr;
+		}
 	} else {
 		/* The operand sizes should be the same, so just pick one */
 		expr->size = operand1->size;
@@ -2861,6 +2869,11 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		}
 
 		expr->name = expr_str(expr, 0);
+		if (IS_ERR(expr->name)) {
+			ret = PTR_ERR(expr->name);
+			expr->name = NULL;
+			goto free_expr;
+		}
 	}
 
 	return expr;
-- 
2.50.1 (Apple Git-155)

[PATCH v4 2/2] tracing: Bound histogram expression strings with seq_buf

[Pengpeng Hou]

expr_str() allocates a fixed MAX_FILTER_STR_VAL buffer and then builds
expression names with a series of raw strcat() appends. Nested operands,
constants and field flags can push the rendered string past that fixed
limit before the name is attached to the hist field.

Build the expression strings with seq_buf and return -E2BIG when the
rendered name would exceed MAX_FILTER_STR_VAL.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
Changes since v3: https://lore.kernel.org/all/20260417223002.2-tracing-expr-v3-pengpeng@iscas.ac.cn/
- rebase on top of v7.1-rc3
- keep the ERR_PTR() conversion in patch 1
- use seq_buf for expression construction and return -E2BIG on overflow

 kernel/trace/trace_events_hist.c | 62 +++++++++++++++++++-------------
 1 file changed, 38 insertions(+), 24 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 0b33bb8ef6f7..c878dc8f0cb9 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -8,6 +8,7 @@
 #include <linux/module.h>
 #include <linux/kallsyms.h>
 #include <linux/security.h>
+#include <linux/seq_buf.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/stacktrace.h>
@@ -1743,33 +1744,37 @@ static const char *get_hist_field_flags(struct hist_field *hist_field)
 	return flags_str;
 }
 
-static void expr_field_str(struct hist_field *field, char *expr)
+static bool expr_field_str(struct hist_field *field, struct seq_buf *s)
 {
+	const char *field_name;
+
 	if (field->flags & HIST_FIELD_FL_VAR_REF) {
 		if (!field->system)
-			strcat(expr, "$");
-	} else if (field->flags & HIST_FIELD_FL_CONST) {
-		char str[HIST_CONST_DIGITS_MAX];
+			seq_buf_putc(s, '$');
+	} else if (field->flags & HIST_FIELD_FL_CONST)
+		seq_buf_printf(s, "%llu", field->constant);
 
-		snprintf(str, HIST_CONST_DIGITS_MAX, "%llu", field->constant);
-		strcat(expr, str);
-	}
+	field_name = hist_field_name(field, 0);
+	if (!field_name)
+		return false;
 
-	strcat(expr, hist_field_name(field, 0));
+	seq_buf_puts(s, field_name);
 
 	if (field->flags && !(field->flags & HIST_FIELD_FL_VAR_REF)) {
 		const char *flags_str = get_hist_field_flags(field);
 
-		if (flags_str) {
-			strcat(expr, ".");
-			strcat(expr, flags_str);
-		}
+		if (flags_str)
+			seq_buf_printf(s, ".%s", flags_str);
 	}
+
+	seq_buf_str(s);
+	return !seq_buf_has_overflowed(s);
 }
 
 static char *expr_str(struct hist_field *field, unsigned int level)
 {
 	char *expr __free(kfree) = NULL;
+	struct seq_buf s;
 
 	if (level > 1)
 		return ERR_PTR(-EINVAL);
@@ -1778,47 +1783,56 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 	if (!expr)
 		return ERR_PTR(-ENOMEM);
 
+	seq_buf_init(&s, expr, MAX_FILTER_STR_VAL);
+
 	if (!field->operands[0]) {
-		expr_field_str(field, expr);
+		if (!expr_field_str(field, &s))
+			return ERR_PTR(-E2BIG);
+
 		return_ptr(expr);
 	}
 
 	if (field->operator == FIELD_OP_UNARY_MINUS) {
-		char *subexpr;
+		char *subexpr __free(kfree) = NULL;
 
-		strcat(expr, "-(");
+		seq_buf_puts(&s, "-(");
 		subexpr = expr_str(field->operands[0], ++level);
 		if (IS_ERR(subexpr))
 			return subexpr;
 
-		strcat(expr, subexpr);
-		strcat(expr, ")");
+		seq_buf_puts(&s, subexpr);
+		seq_buf_putc(&s, ')');
+		seq_buf_str(&s);
 
-		kfree(subexpr);
+		if (seq_buf_has_overflowed(&s))
+			return ERR_PTR(-E2BIG);
 
 		return_ptr(expr);
 	}
 
-	expr_field_str(field->operands[0], expr);
+	if (!expr_field_str(field->operands[0], &s))
+		return ERR_PTR(-E2BIG);
 
 	switch (field->operator) {
 	case FIELD_OP_MINUS:
-		strcat(expr, "-");
+		seq_buf_putc(&s, '-');
 		break;
 	case FIELD_OP_PLUS:
-		strcat(expr, "+");
+		seq_buf_putc(&s, '+');
 		break;
 	case FIELD_OP_DIV:
-		strcat(expr, "/");
+		seq_buf_putc(&s, '/');
 		break;
 	case FIELD_OP_MULT:
-		strcat(expr, "*");
+		seq_buf_putc(&s, '*');
 		break;
 	default:
 		return ERR_PTR(-EINVAL);
 	}
 
-	expr_field_str(field->operands[1], expr);
+	if (seq_buf_has_overflowed(&s) ||
+	    !expr_field_str(field->operands[1], &s))
+		return ERR_PTR(-E2BIG);
 
 	return_ptr(expr);
 }
-- 
2.50.1 (Apple Git-155)

Re: [PATCH v4 2/2] tracing: Bound histogram expression strings with seq_buf

[Steven Rostedt]

On Thu, 21 May 2026 10:28:17 +0800
Pengpeng Hou <pengpeng@iscas.ac.cn> wrote:

> @@ -1778,47 +1783,56 @@ static char *expr_str(struct hist_field *field, unsigned int level)
>  	if (!expr)
>  		return ERR_PTR(-ENOMEM);
>  
> +	seq_buf_init(&s, expr, MAX_FILTER_STR_VAL);
> +
>  	if (!field->operands[0]) {
> -		expr_field_str(field, expr);
> +		if (!expr_field_str(field, &s))
> +			return ERR_PTR(-E2BIG);
> +
>  		return_ptr(expr);
>  	}
>  
>  	if (field->operator == FIELD_OP_UNARY_MINUS) {
> -		char *subexpr;
> +		char *subexpr __free(kfree) = NULL;
>  
> -		strcat(expr, "-(");
> +		seq_buf_puts(&s, "-(");
>  		subexpr = expr_str(field->operands[0], ++level);
>  		if (IS_ERR(subexpr))
>  			return subexpr;
>  
> -		strcat(expr, subexpr);
> -		strcat(expr, ")");
> +		seq_buf_puts(&s, subexpr);
> +		seq_buf_putc(&s, ')');
> +		seq_buf_str(&s);
>  
> -		kfree(subexpr);
> +		if (seq_buf_has_overflowed(&s))
> +			return ERR_PTR(-E2BIG);
>  
>  		return_ptr(expr);
>  	}

Wouldn't the above if statement be a lot nicer as:

 	if (field->operator == FIELD_OP_UNARY_MINUS) {
		char *subexpr;

		subexpr = expr_str(field->operands[0], ++level);
		if (IS_ERR(subexpr))
			return subexpr;

		seq_buf_printf(&s, "-(%s)", subexpr); 
		seq_buf_str(&s);
  		kfree(subexpr);

		if (seq_buf_has_overflowed(&s))
			return ERR_PTR(-E2BIG);
 
		return_ptr(expr);
 	}

In fact, the above is so simple, you don't even need to use the __free()
guard on subexpr.

BTW, because currently seq_buf_printf() does add a '\0' to the string, I
may update the API for seq_buf to state that you don't need to terminate
after calling that function. So you can leave out the sub_buf_str() after
calling seq_buf_printf().

-- Steve

Re: [PATCH v4 1/2] tracing: Return ERR_PTR() from expr_str()

[Steven Rostedt]

On Thu, 21 May 2026 10:28:16 +0800
Pengpeng Hou <pengpeng@iscas.ac.cn> wrote:

> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 0dbbf6cca9bc..0b33bb8ef6f7 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1769,18 +1769,18 @@ static void expr_field_str(struct hist_field *field, char *expr)
>  
>  static char *expr_str(struct hist_field *field, unsigned int level)
>  {
> -	char *expr;
> +	char *expr __free(kfree) = NULL;

Can you split this into two patches.

1. Change expr to use __free(kfree)

2. Update to use ERR_PTR()

as they are two distinct changes.

Thanks,

-- Steve

>  
>  	if (level > 1)
> -		return NULL;
> +		return ERR_PTR(-EINVAL);
>  
>  	expr = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
>  	if (!expr)
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  
>  	if (!field->operands[0]) {
>  		expr_field_str(field, expr);
> -		return expr;
> +		return_ptr(expr);
>  	}