util.c: check first/last char and allow extra chars

In `invalid_name`.

1 files changed, 26 insertions, 4 deletions

diff --git a/src/firejail/util.c b/src/firejail/util.c
index 78704fa64..6c79c050e 100644
--- a/src/firejail/util.c
+++ b/src/firejail/util.c
@@ -1476,7 +1476,8 @@ int ascii_isxdigit(unsigned char c) {
         return ret;
 }
 
-// allow strict ASCII letters and numbers; names with only numbers are rejected; spaces are rejected
+// Allow only ASCII letters, digits and a few special characters; names with
+// only numbers are rejected; spaces and control characters are rejected.
 int invalid_name(const char *name) {
         const char *c = name;
         int only_numbers = 1;
@@ -1484,13 +1485,34 @@ int invalid_name(const char *name) {
         if (strlen(name) > 253)
                 return 1;
 
+        // must start with alnum
+        if (!ascii_isalnum(*c))
+                return 1;
+        if (!ascii_isdigit(*c))
+                only_numbers = 0;
+        ++c;
+
         while (*c) {
-                if (!ascii_isalnum(*c))
-                        return 1;
-                if (!ascii_isdigit(*c))
+                switch (*c) {
+                case '-':
+                case '.':
+                case '_':
                         only_numbers = 0;
+                        break;
+                default:
+                        if (!ascii_isalnum(*c))
+                                return 1;
+                        if (!ascii_isdigit(*c))
+                                only_numbers = 0;
+                }
                 ++c;
         }
+
+        // must end with alnum
+        --c;
+        if (!ascii_isalnum(*c))
+                return 1;
+
         if (only_numbers)
                 return 1;