gdbstub: Fix buffer overflows in gdb_handle_packet()

Some places in gdb_handle_packet() can get an arbitrary length (most
times directly from the client) and either didn't check it at all or
checked against the wrong value, potentially causing buffer overflows.

Cc: qemu-stable@nongnu.org
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

gdbstub.c

@@ -956,6 +956,13 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
         if (*p == ',')
             p++;
         len = strtoull(p, NULL, 16);
+
+        /* memtohex() doubles the required space */
+        if (len > MAX_PACKET_LENGTH / 2) {
+            put_packet (s, "E22");
+            break;
+        }
+
         if (target_memory_rw_debug(s->g_cpu, addr, mem_buf, len, false) != 0) {
             put_packet (s, "E14");
         } else {
@@ -970,6 +977,12 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
         len = strtoull(p, (char **)&p, 16);
         if (*p == ':')
             p++;
+
+        /* hextomem() reads 2*len bytes */
+        if (len > strlen(p) / 2) {
+            put_packet (s, "E22");
+            break;
+        }
         hextomem(mem_buf, p, len);
         if (target_memory_rw_debug(s->g_cpu, addr, mem_buf, len,
                                    true) != 0) {
@@ -1107,7 +1120,8 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
             cpu = find_cpu(thread);
             if (cpu != NULL) {
                 cpu_synchronize_state(cpu);
-                len = snprintf((char *)mem_buf, sizeof(mem_buf),
+                /* memtohex() doubles the required space */
+                len = snprintf((char *)mem_buf, sizeof(buf) / 2,
                                "CPU#%d [%s]", cpu->cpu_index,
                                cpu->halted ? "halted " : "running");
                 memtohex(buf, mem_buf, len);
@@ -1136,8 +1150,8 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
                 put_packet(s, "E01");
                 break;
             }
-            hextomem(mem_buf, p + 5, len);
             len = len / 2;
+            hextomem(mem_buf, p + 5, len);
             mem_buf[len++] = 0;
             qemu_chr_be_write(s->mon_chr, mem_buf, len);
             put_packet(s, "OK");