aplay: fix buffer overflow and tainted format string

Prior this commit, memcpy from names[0] to format[] will overwrite if
strlen(names[0]) is greater than 1024. Also, the length of malloc()ed
names[channel] is insufficient, leading to another buffer overwriting
when calling sprintf(). Moreover, the format string of sprintf()
can be controlled by user input. An attacker can exploit this weakness
to crash the program, disclose information or even execute arbitrary
code.

Fix by allocating enough space for arrays and using constant expressions
as the format strings.

Fixes: #246
Signed-off-by: Mingjie Shen <[email protected]>
Signed-off-by: Jaroslav Kysela <[email protected]>

aplay/aplay.c

@@ -3436,14 +3436,14 @@ static void playbackv(char **names, unsigned int count)
 
 	if (count == 1 && channels > 1) {
 		size_t len = strlen(names[0]);
-		char format[1024];
-		memcpy(format, names[0], len);
-		strcpy(format + len, ".%d");
-		len += 4;
+		char buf[len + 1];
+		strcpy(buf, names[0]);
+		/* 1 for "." + 3 for channel (<= 256) + 1 for null terminator */
+		len += 5;
 		names = malloc(sizeof(*names) * channels);
 		for (channel = 0; channel < channels; ++channel) {
 			names[channel] = malloc(len);
-			sprintf(names[channel], format, channel);
+			snprintf(names[channel], len, "%s.%d", buf, channel);
 		}
 		alloced = 1;
 	} else if (count != channels) {
@@ -3489,14 +3489,14 @@ static void capturev(char **names, unsigned int count)
 
 	if (count == 1) {
 		size_t len = strlen(names[0]);
-		char format[1024];
-		memcpy(format, names[0], len);
-		strcpy(format + len, ".%d");
-		len += 4;
+		char buf[len + 1];
+		strcpy(buf, names[0]);
+		/* 1 for "." + 3 for channel (<= 256) + 1 for null terminator */
+		len += 5;
 		names = malloc(sizeof(*names) * channels);
 		for (channel = 0; channel < channels; ++channel) {
 			names[channel] = malloc(len);
-			sprintf(names[channel], format, channel);
+			snprintf(names[channel], len, "%s.%d", buf, channel);
 		}
 		alloced = 1;
 	} else if (count != channels) {