die_if_bad_username: tighten up a bit

function                                             old     new   delta
die_if_bad_username                                   77      97     +20

Based on patches from Tito.
The changes are:
better comments
we disallow '@' now - in practice such usernames will be unusable
use of the portable filename character set plus '$'
don't use isalnum as it allows non-ASCII letters in legacy 8-bit locales (pointed out by Rich Felker)
enforce maximum length of LOGIN_NAME_MAX (including NUL)
don't allow '$', '.', and '-' as first char
don't print the illegal char in error message as if it is a wide char it will be unreadable
print the position of the illegal character

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/libbb/die_if_bad_username.c b/libbb/die_if_bad_username.c
index 9946e3a..cf1297b 100644 (file)
--- a/libbb/die_if_bad_username.c
+++ b/libbb/die_if_bad_username.c
@@ -18,23 +18,45 @@
 
 void FAST_FUNC die_if_bad_username(const char *name)
 {
-       /* 1st char being dash or dot isn't valid: */
-       goto skip;
-       /* For example, name like ".." can make adduser
-        * chown "/home/.." recursively - NOT GOOD
+       const char *start = name;
+
+       /* 1st char being dash or dot isn't valid:
+        * for example, name like ".." can make adduser
+        * chown "/home/.." recursively - NOT GOOD.
+        * Name of just a single "$" is also rejected.
         */
+       goto skip;
 
        do {
-               if (*name == '-' || *name == '.')
+               unsigned char ch;
+
+               /* These chars are valid unless they are at the 1st pos: */
+               if (*name == '-'
+                || *name == '.'
+               /* $ is allowed if it's the last char: */
+                || (*name == '$' && !name[1])
+               ) {
                        continue;
+               }
  skip:
-               if (isalnum(*name)
-                || *name == '_'
-                || *name == '@'
-                || (*name == '$' && !name[1])
+               ch = *name;
+               if (ch == '_'
+               /* || ch == '@' -- we disallow this too. Think about "user@host" */
+               /* open-coded isalnum: */
+                || (ch >= '0' && ch <= '9')
+                || ((ch|0x20) >= 'a' && (ch|0x20) <= 'z')
                ) {
                        continue;
                }
-               bb_error_msg_and_die("illegal character '%c'", *name);
+               bb_error_msg_and_die("illegal character with code %u at position %u",
+                               (unsigned)ch, (unsigned)(name - start));
        } while (*++name);
+
+       /* The minimum size of the login name is one char or two if
+        * last char is the '$'. Violations of this are caught above.
+        * The maximum size of the login name is LOGIN_NAME_MAX
+        * including the terminating null byte.
+        */
+       if (name - start >= LOGIN_NAME_MAX)
+               bb_error_msg_and_die("name is too long");
 }