[PATCH 12/27] perf cpumap: Reject RANGE_CPUS with start_cpu > end_cpu

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

cpu_map__from_range() computes nr_cpus as end_cpu - start_cpu + 1.
When a crafted perf.data has start_cpu > end_cpu, this wraps to a
huge value, causing perf_cpu_map__empty_new() to attempt a massive
allocation.

Return NULL when the range is inverted.

Also clamp any_cpu to boolean (0 or 1) since it is added to the
allocation count — a crafted value > 1 would inflate the map size.

Harden cpu_map__from_mask() to reject unsupported long_size values
(anything other than 4 or 8), preventing misinterpretation of the
mask data layout.

Snapshot mmap'd fields via READ_ONCE() into locals to prevent
TOCTOU re-reads — the data pointer references MAP_SHARED mmap'd
memory that could theoretically change between reads on a
FUSE-backed file:

- cpu_map__from_range(): snapshot start_cpu, end_cpu, any_cpu
- cpu_map__from_entries(): snapshot nr and each cpu[i] element
- cpu_map__from_mask(): snapshot long_size (before validation,
  closing the check-then-read gap), mask_nr
- perf_record_cpu_map_data__read_one_mask(): add u16 long_size
  parameter so callers pass the validated copy instead of
  re-reading data->mask32_data.long_size from mmap'd memory

Reported-by: sashiko-bot@kernel.org # Running on a local machine
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Assisted-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/cpumap.c | 62 +++++++++++++++++++++++++++++-----------
 1 file changed, 45 insertions(+), 17 deletions(-)

diff --git a/tools/perf/util/cpumap.c b/tools/perf/util/cpumap.c
index 11922e1ded844a03..b1e5c29c6e3ec8df 100644
--- a/tools/perf/util/cpumap.c
+++ b/tools/perf/util/cpumap.c
@@ -10,6 +10,7 @@
 #include <linux/bitmap.h>
 #include "asm/bug.h"
 
+#include <linux/compiler.h>
 #include <linux/ctype.h>
 #include <linux/zalloc.h>
 #include <internal/cpumap.h>
@@ -40,15 +41,16 @@ bool perf_record_cpu_map_data__test_bit(int i,
 
 /* Read ith mask value from data into the given 64-bit sized bitmap */
 static void perf_record_cpu_map_data__read_one_mask(const struct perf_record_cpu_map_data *data,
-						    int i, unsigned long *bitmap)
+						    int i, unsigned long *bitmap,
+						    u16 long_size)
 {
 #if __SIZEOF_LONG__ == 8
-	if (data->mask32_data.long_size == 4)
+	if (long_size == 4)
 		bitmap[0] = data->mask32_data.mask[i];
 	else
 		bitmap[0] = data->mask64_data.mask[i];
 #else
-	if (data->mask32_data.long_size == 4) {
+	if (long_size == 4) {
 		bitmap[0] = data->mask32_data.mask[i];
 		bitmap[1] = 0;
 	} else {
@@ -64,24 +66,27 @@ static void perf_record_cpu_map_data__read_one_mask(const struct perf_record_cpu
 }
 static struct perf_cpu_map *cpu_map__from_entries(const struct perf_record_cpu_map_data *data)
 {
+	/* Snapshot nr — data is mmap'd and could change between reads */
+	u16 nr = READ_ONCE(data->cpus_data.nr);
 	struct perf_cpu_map *map;
 
-	map = perf_cpu_map__empty_new(data->cpus_data.nr);
+	map = perf_cpu_map__empty_new(nr);
 	if (!map)
 		return NULL;
 
-	for (unsigned int i = 0; i < data->cpus_data.nr; i++) {
+	for (unsigned int i = 0; i < nr; i++) {
+		u16 cpu = READ_ONCE(data->cpus_data.cpu[i]);
 		/*
 		 * Special treatment for -1, which is not real cpu number,
 		 * and we need to use (int) -1 to initialize map[i],
 		 * otherwise it would become 65535.
 		 */
-		if (data->cpus_data.cpu[i] == (u16) -1) {
+		if (cpu == (u16) -1) {
 			RC_CHK_ACCESS(map)->map[i].cpu = -1;
-		} else if (data->cpus_data.cpu[i] < INT16_MAX) {
-			RC_CHK_ACCESS(map)->map[i].cpu = (int16_t) data->cpus_data.cpu[i];
+		} else if (cpu < INT16_MAX) {
+			RC_CHK_ACCESS(map)->map[i].cpu = (int16_t) cpu;
 		} else {
-			pr_err("Invalid cpumap entry %u\n", data->cpus_data.cpu[i]);
+			pr_err("Invalid cpumap entry %u\n", cpu);
 			perf_cpu_map__put(map);
 			return NULL;
 		}
@@ -93,11 +98,21 @@ static struct perf_cpu_map *cpu_map__from_entries(const struct perf_record_cpu_m
 static struct perf_cpu_map *cpu_map__from_mask(const struct perf_record_cpu_map_data *data)
 {
 	DECLARE_BITMAP(local_copy, 64);
-	int weight = 0, mask_nr = data->mask32_data.nr;
+	int weight = 0, mask_nr;
+	/* Snapshot before validation — data is mmap'd and could change */
+	u16 long_size = READ_ONCE(data->mask32_data.long_size);
 	struct perf_cpu_map *map;
 
+	/* long_size must be 4 or 8; other values overflow cpus_per_i below */
+	if (long_size != 4 && long_size != 8) {
+		pr_warning("WARNING: cpu_map mask: unsupported long_size %u\n", long_size);
+		return NULL;
+	}
+
+	mask_nr = READ_ONCE(data->mask32_data.nr);
+
 	for (int i = 0; i < mask_nr; i++) {
-		perf_record_cpu_map_data__read_one_mask(data, i, local_copy);
+		perf_record_cpu_map_data__read_one_mask(data, i, local_copy, long_size);
 		weight += bitmap_weight(local_copy, 64);
 	}
 
@@ -106,11 +121,14 @@ static struct perf_cpu_map *cpu_map__from_mask(const struct perf_record_cpu_map_
 		return NULL;
 
 	for (int i = 0, j = 0; i < mask_nr; i++) {
-		int cpus_per_i = (i * data->mask32_data.long_size  * BITS_PER_BYTE);
+		int cpus_per_i = (i * long_size * BITS_PER_BYTE);
 		int cpu;
 
-		perf_record_cpu_map_data__read_one_mask(data, i, local_copy);
+		perf_record_cpu_map_data__read_one_mask(data, i, local_copy, long_size);
 		for_each_set_bit(cpu, local_copy, 64) {
+			/* Guard against more set bits than the first pass counted */
+			if (j >= weight)
+				break;
 			if (cpu + cpus_per_i < INT16_MAX) {
 				RC_CHK_ACCESS(map)->map[j++].cpu = cpu + cpus_per_i;
 			} else {
@@ -126,18 +144,28 @@ static struct perf_cpu_map *cpu_map__from_mask(const struct perf_record_cpu_map_
 
 static struct perf_cpu_map *cpu_map__from_range(const struct perf_record_cpu_map_data *data)
 {
+	/* Snapshot fields — data is mmap'd and could change between reads */
+	u16 start_cpu = READ_ONCE(data->range_cpu_data.start_cpu);
+	u16 end_cpu = READ_ONCE(data->range_cpu_data.end_cpu);
+	u16 any_cpu = READ_ONCE(data->range_cpu_data.any_cpu);
 	struct perf_cpu_map *map;
 	unsigned int i = 0;
 
-	map = perf_cpu_map__empty_new(data->range_cpu_data.end_cpu -
-				data->range_cpu_data.start_cpu + 1 + data->range_cpu_data.any_cpu);
+	if (end_cpu < start_cpu) {
+		pr_warning("WARNING: cpu_map range: end_cpu %u < start_cpu %u\n",
+			   end_cpu, start_cpu);
+		return NULL;
+	}
+
+	/* any_cpu is boolean (0 or 1), not a count — clamp to avoid inflated nr */
+	map = perf_cpu_map__empty_new(end_cpu - start_cpu + 1 + !!any_cpu);
 	if (!map)
 		return NULL;
 
-	if (data->range_cpu_data.any_cpu)
+	if (any_cpu)
 		RC_CHK_ACCESS(map)->map[i++].cpu = -1;
 
-	for (int cpu = data->range_cpu_data.start_cpu; cpu <= data->range_cpu_data.end_cpu;
+	for (int cpu = start_cpu; cpu <= end_cpu;
 	     i++, cpu++) {
 		if (cpu < INT16_MAX) {
 			RC_CHK_ACCESS(map)->map[i].cpu = cpu;
-- 
2.54.0