[PATCH] msvcrt: Verify format string before reading past end of it

From: Michał Janiszewski <janisozaur(a)gmail.com>

In some cases, e.g. unterminated selection specifier (%[]) could make
scanf() family of functions could keep reading from the format string
past end of it.

Add a check to verify when format string ends, rather than blindly
expect the termination to happen.

Signed-off-by: Michał Janiszewski <janisozaur(a)gmail.com>
---
 dlls/msvcrt/scanf.h       | 2 +-
 dlls/msvcrt/tests/scanf.c | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/dlls/msvcrt/scanf.h b/dlls/msvcrt/scanf.h
index 0903d6909a..68585468fe 100644
--- a/dlls/msvcrt/scanf.h
+++ b/dlls/msvcrt/scanf.h
@@ -637,7 +637,7 @@ _FUNCTION_ {
                     while(*format && (*format != ']')) {
 			/* According to msdn:
 			 * "Note that %[a-z] and %[z-a] are interpreted as equivalent to %[abcde...z]." */
-			if((*format == '-') && (*(format + 1) != ']')) {
+			if((*format == '-') && *(format + 1) && (*(format + 1) != ']')) {
 			    if ((*(format - 1)) < *(format + 1))
 				RtlSetBits(&bitMask, *(format - 1) +1 , *(format + 1) - *(format - 1));
 			    else
diff --git a/dlls/msvcrt/tests/scanf.c b/dlls/msvcrt/tests/scanf.c
index b7244835ac..e1e351e0bb 100644
--- a/dlls/msvcrt/tests/scanf.c
+++ b/dlls/msvcrt/tests/scanf.c
@@ -294,6 +294,12 @@ static void test_sscanf_s(void)
     ret = psscanf_s("123", "%3c", buf, 3);
     ok(!strcmp("123a", buf), "buf = %s\n", buf);
 
+    /* Test to verify how unterminated and invalid sequence gets handled */
+    memset(buf, 'a', sizeof(buf));
+    ret = psscanf_s(" ", "%[-", buf, 2);
+    ok(ret == 1, "Wrong number of arguments read: %d\n", ret);
+    ok(!strcmp(" ", buf), "buf = %s\n", buf);
+
     i = 1;
     ret = psscanf_s("123 123", "%s %d", buf, 2, &i);
     ok(ret == 0, "Wrong number of arguments read: %d\n", ret);
-- 
2.18.0