selftests/x86: Clean up and document sscanf() usage

Replace a couple of magically connected buffer length literal constants with
a common definition that makes their relationship obvious. Also document
why our sscanf() usage is safe.

No intended functional changes.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kselftest@vger.kernel.org
Cc: shuah@kernel.org
Link: http://lkml.kernel.org/r/20180211205924.GA23210@light.dominikbrodowski.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 16 insertions, 6 deletions

diff --git a/tools/testing/selftests/x86/test_vdso.c b/tools/testing/selftests/x86/test_vdso.c
index 558c8207e7b9..235259011704 100644
--- a/tools/testing/selftests/x86/test_vdso.c
+++ b/tools/testing/selftests/x86/test_vdso.c
@@ -26,6 +26,9 @@
 # endif
 #endif
 
+/* max length of lines in /proc/self/maps - anything longer is skipped here */
+#define MAPS_LINE_LEN 128
+
 int nerrs = 0;
 
 typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
@@ -37,17 +40,19 @@ static void *vsyscall_getcpu(void)
 {
 #ifdef __x86_64__
         FILE *maps;
-        char line[128];
+        char line[MAPS_LINE_LEN];
         bool found = false;
 
         maps = fopen("/proc/self/maps", "r");
         if (!maps) /* might still be present, but ignore it here, as we test vDSO not vsyscall */
                 return NULL;
 
-        while (fgets(line, sizeof(line), maps)) {
+        while (fgets(line, MAPS_LINE_LEN, maps)) {
                 char r, x;
                 void *start, *end;
-                char name[128];
+                char name[MAPS_LINE_LEN];
+
+                /* sscanf() is safe here as strlen(name) >= strlen(line) */
                 if (sscanf(line, "%p-%p %c-%cp %*x %*x:%*x %*u %s",
                            &start, &end, &r, &x, name) != 5)
                         continue;
diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
index 7a744fa7b786..be81621446f0 100644
--- a/tools/testing/selftests/x86/test_vsyscall.c
+++ b/tools/testing/selftests/x86/test_vsyscall.c
@@ -33,6 +33,9 @@
 # endif
 #endif
 
+/* max length of lines in /proc/self/maps - anything longer is skipped here */
+#define MAPS_LINE_LEN 128
+
 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
                        int flags)
 {
@@ -98,7 +101,7 @@ static int init_vsys(void)
 #ifdef __x86_64__
         int nerrs = 0;
         FILE *maps;
-        char line[128];
+        char line[MAPS_LINE_LEN];
         bool found = false;
 
         maps = fopen("/proc/self/maps", "r");
@@ -108,10 +111,12 @@ static int init_vsys(void)
                 return 0;
         }
 
-        while (fgets(line, sizeof(line), maps)) {
+        while (fgets(line, MAPS_LINE_LEN, maps)) {
                 char r, x;
                 void *start, *end;
-                char name[128];
+                char name[MAPS_LINE_LEN];
+
+                /* sscanf() is safe here as strlen(name) >= strlen(line) */
                 if (sscanf(line, "%p-%p %c-%cp %*x %*x:%*x %*u %s",
                            &start, &end, &r, &x, name) != 5)
                         continue;