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DescriptionMiroslav Vadkerti
2012-04-17 16:35:50 UTC
Description of problem:
lgroupmod -M doesn't check strings for ':'.
Version-Release number of selected component (if applicable):
libuser-0.56.13-5.el6
How reproducible:
Always
Steps to Reproduce:
# lgroupadd testgroup
# lgroupmod -M a:b:c,d:e:f testgroup
# grep testgroup /etc/group
testgroup:x:502:a:b:c,d:e:f
Actual Results:
lgroupmod -M accepts user name containing ':'.
Expected Results:
lgroupmod -M refuses user name containing ':'.
Thanks for your report.
In general:
The last field on the line is special: adding colons to it does not add any field splitting ambiguity. libuser therefore explicitly allows ':' in the last field.
glibc's parsers do not recognize the ':' as a separator in that case (in particular, you can have a ':' in user's shell). On the other hand, shadow-utils's parsers do recognize the ':' as terminating even the last field on the line, so the situation is ambiguous.
Therefore, libuser will always differ from one of glibc and shadow-utils.
Given that the field splitting does not have any security impact, and the file format is not really strictly defined, I think leaving the existing code is fine. We can't promise that it will work, but we don't have a really good reason to prohibit it, either.
In this specific case (also applies to the member list, but not the administrator list, in /etc/gshadow):
Anyone using the /etc/passwd file will not be able to add an user named "a:b:c", so any such invocation is invalid in any case, regardless of how glibc or shadow-utils interpret it. (In theory, a user named "a:b:c" might be defined in LDAP, where the ":" character is not prohibited, and /etc/group could refer to it - but that's extremely brittle).
Please reopen this if I have overlooked a reason to prohibit the ':' in the last field.