[PATCH v3 5/7] selftests/powerpc: Parse long/unsigned long value safely

[Benjamin Gray]

Often a file is expected to hold an integral value. Existing functions
will use a C stdlib function like atoi or strtol to parse the file.
These operations are error prone, with complicated error conditions
(atoi returns 0 if not a number, and is undefined behaviour if not in
range. strtol returns 0 if not a number, and LONG_MIN/MAX if not in
range + sets errno to ERANGE).

Add a dedicated parse function that accounts for these error conditions
so tests can safely parse numbers without undetected bad data. It's a
bit ugly to generate the functions through a macro, but it beats copying
the error check logic multiple times over.

Signed-off-by: Benjamin Gray <bgray at linux.ibm.com>
---
 .../testing/selftests/powerpc/include/utils.h |  5 ++
 tools/testing/selftests/powerpc/pmu/lib.c     |  9 ++--
 tools/testing/selftests/powerpc/utils.c       | 53 +++++++++++++++++--
 3 files changed, 59 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/powerpc/include/utils.h b/tools/testing/selftests/powerpc/include/utils.h
index de5e3790f397..b82e143a07c6 100644
--- a/tools/testing/selftests/powerpc/include/utils.h
+++ b/tools/testing/selftests/powerpc/include/utils.h
@@ -33,6 +33,11 @@ void *get_auxv_entry(int type);
 
 int pick_online_cpu(void);
 
+int parse_int(const char *buffer, size_t count, int *result, int base);
+int parse_long(const char *buffer, size_t count, long *result, int base);
+int parse_uint(const char *buffer, size_t count, unsigned int *result, int base);
+int parse_ulong(const char *buffer, size_t count, unsigned long *result, int base);
+
 int read_file(const char *path, char *buf, size_t count, size_t *len);
 int write_file(const char *path, const char *buf, size_t count);
 int read_debugfs_file(const char *debugfs_file, char *buf, size_t count);
diff --git a/tools/testing/selftests/powerpc/pmu/lib.c b/tools/testing/selftests/powerpc/pmu/lib.c
index e8960e7a1271..771658278f55 100644
--- a/tools/testing/selftests/powerpc/pmu/lib.c
+++ b/tools/testing/selftests/powerpc/pmu/lib.c
@@ -192,16 +192,15 @@ bool require_paranoia_below(int level)
 {
 	int err;
 	long current;
-	char *end, buf[16];
+	char buf[16] = {0};
+	char *end;
 
-	if ((err = read_file(PARANOID_PATH, buf, sizeof(buf), NULL))) {
+	if ((err = read_file(PARANOID_PATH, buf, sizeof(buf) - 1, NULL))) {
 		printf("Couldn't read " PARANOID_PATH "?\n");
 		return false;
 	}
 
-	current = strtol(buf, &end, 10);
-
-	if (end == buf) {
+	if ((err = parse_long(buf, sizeof(buf), &current, 10))) {
 		printf("Couldn't parse " PARANOID_PATH "?\n");
 		return false;
 	}
diff --git a/tools/testing/selftests/powerpc/utils.c b/tools/testing/selftests/powerpc/utils.c
index 8593e67ce779..c82539fd44f1 100644
--- a/tools/testing/selftests/powerpc/utils.c
+++ b/tools/testing/selftests/powerpc/utils.c
@@ -8,6 +8,8 @@
 #include <elf.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <inttypes.h>
+#include <limits.h>
 #include <link.h>
 #include <sched.h>
 #include <stdio.h>
@@ -113,6 +115,53 @@ int write_debugfs_file(const char *subpath, const char *buf, size_t count)
 	return write_file(path, buf, count);
 }
 
+#define TYPE_MIN(x)				\
+	_Generic((x),				\
+		int:		INT_MIN,	\
+		long:		LONG_MIN,	\
+		unsigned int:	0,		\
+		unsigned long:	0)
+
+#define TYPE_MAX(x)				\
+	_Generic((x),				\
+		int:		INT_MAX,	\
+		long:		LONG_MAX,	\
+		unsigned int:	INT_MAX,	\
+		unsigned long:	LONG_MAX)
+
+#define define_parse_number(fn, type, super_type)				\
+	int fn(const char *buffer, size_t count, type *result, int base)	\
+	{									\
+		char *end;							\
+		super_type parsed;						\
+										\
+		errno = 0;							\
+		parsed = _Generic(parsed,					\
+				  intmax_t:	strtoimax,			\
+				  uintmax_t:	strtoumax)(buffer, &end, base);	\
+										\
+		if (errno == ERANGE ||						\
+		    parsed < TYPE_MIN(*result) || parsed > TYPE_MAX(*result))	\
+			return ERANGE;						\
+										\
+		/* Require at least one digit */				\
+		if (end == buffer)						\
+			return EINVAL;						\
+										\
+		/* Require all remaining characters be whitespace-ish */	\
+		for (; end < buffer + count; end++)				\
+			if (!(*end == ' ' || *end == '\n' || *end == '\0'))	\
+				return EINVAL;					\
+										\
+		*result = parsed;						\
+		return 0;							\
+	}
+
+define_parse_number(parse_int, int, intmax_t);
+define_parse_number(parse_long, long, intmax_t);
+define_parse_number(parse_uint, unsigned int, uintmax_t);
+define_parse_number(parse_ulong, unsigned long, uintmax_t);
+
 void *find_auxv_entry(int type, char *auxv)
 {
 	ElfW(auxv_t) *p;
@@ -213,9 +262,7 @@ int read_debugfs_int(const char *debugfs_file, int *result)
 	if ((err = read_debugfs_file(debugfs_file, value, sizeof(value) - 1)))
 		return err;
 
-	*result = atoi(value);
-
-	return 0;
+	return parse_int(value, sizeof(value), result, 10);
 }
 
 int write_debugfs_int(const char *debugfs_file, int result)
-- 
2.38.1