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

Web:        https://git.kernel.org/torvalds/c/d8e92de8ef952bed88c56c7a44c02d8dcae0984e
Commit:     d8e92de8ef952bed88c56c7a44c02d8dcae0984e
Parent:     198ee8e17502da2634f7366395db1d77630e0219
Refname:    refs/heads/master
Author:     Dominik Brodowski <[email protected]>
AuthorDate: Sun Feb 11 21:59:24 2018 +0100
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue Feb 13 09:04:56 2018 +0100

    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 <[email protected]>
    Signed-off-by: Dominik Brodowski <[email protected]>
    Cc: Andrew Lutomirski <[email protected]>
    Cc: Andy Lutomirski <[email protected]>
    Cc: Linus Torvalds <[email protected]>
    Cc: Peter Zijlstra <[email protected]>
    Cc: Thomas Gleixner <[email protected]>
    Cc: [email protected]
    Cc: [email protected]
    Link: http://lkml.kernel.org/r/[email protected]
    Signed-off-by: Ingo Molnar <[email protected]>
---
 tools/testing/selftests/x86/test_vdso.c     | 11 ++++++++---
 tools/testing/selftests/x86/test_vsyscall.c | 11 ++++++++---
 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;
--
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