tools lib api: Fix missing null termination in filename__read_int/ull()

[ Upstream commit 52b1f96 ]

filename__read_int() passes a stack buffer to read() using the full
sizeof(line) and then hands it to atoi() without null-terminating.
If a sysfs file fills the 64-byte buffer exactly, atoi() reads past
the array into uninitialized stack memory.

filename__read_ull_base() has the same issue with strtoull().

Fix both by reading sizeof(line) - 1 bytes and explicitly
null-terminating after a successful read.

Fixes: 3a35112 ("tools lib fs: Adopt filename__read_int from tools/perf/")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: acmel

tools/lib/api/fs/fs.c

@@ -293,11 +293,14 @@ int filename__read_int(const char *filename, int *value)
 {
 	char line[64];
 	int fd = open(filename, O_RDONLY), err = -1;
+	ssize_t n;
 
 	if (fd < 0)
 		return -1;
 
-	if (read(fd, line, sizeof(line)) > 0) {
+	n = read(fd, line, sizeof(line) - 1);
+	if (n > 0) {
+		line[n] = '\0';
 		*value = atoi(line);
 		err = 0;
 	}
@@ -311,11 +314,14 @@ static int filename__read_ull_base(const char *filename,
 {
 	char line[64];
 	int fd = open(filename, O_RDONLY), err = -1;
+	ssize_t n;
 
 	if (fd < 0)
 		return -1;
 
-	if (read(fd, line, sizeof(line)) > 0) {
+	n = read(fd, line, sizeof(line) - 1);
+	if (n > 0) {
+		line[n] = '\0';
 		*value = strtoull(line, NULL, base);
 		if (*value != ULLONG_MAX)
 			err = 0;