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die_if_bad_username: tighten up a bit

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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>
This commit is contained in:
Denys Vlasenko 2011-08-09 04:05:13 +02:00
parent 6e42b89b8d
commit 7485086f1e
1 changed files with 33 additions and 11 deletions
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44
libbb/die_if_bad_username.c
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@ -18,23 +18,45 @@
void FAST_FUNC die_if_bad_username(const char *name) void FAST_FUNC die_if_bad_username(const char *name)
{ {
/* 1st char being dash or dot isn't valid: */ const char *start = name;
goto skip;
/* For example, name like ".." can make adduser /* 1st char being dash or dot isn't valid:
* chown "/home/.." recursively - NOT GOOD * for example, name like ".." can make adduser
* chown "/home/.." recursively - NOT GOOD.
* Name of just a single "$" is also rejected.
*/ */
goto skip;
do { do {
if (*name == '-' || *name == '.') unsigned char ch;
continue;
skip: /* These chars are valid unless they are at the 1st pos: */
if (isalnum(*name) if (*name == '-'
|| *name == '_' || *name == '.'
|| *name == '@' /* $ is allowed if it's the last char: */
|| (*name == '$' && !name[1]) || (*name == '$' && !name[1])
) { ) {
continue; continue;
} }
bb_error_msg_and_die("illegal character '%c'", *name); skip:
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 with code %u at position %u",
(unsigned)ch, (unsigned)(name - start));
} while (*++name); } 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");
} }