"A heap-based buffer overflow was found in __nss_hostname_digits_dots(), which is used by the gethostbyname() and gethostbyname2() glibc function call. A remote attacker could use this flaw to execute arbitary code with the permissions of the user running the application."
Note that this is a HEAD link, so if there are changes after I post this they should appear. I don't claim to have spotted the suspicious code (it's not ... super-accessible), just wanted to provide a link to the file in question.
> Avoid arbitrary limits on the length or number of any data structure, including file names, lines, files, and symbols, by allocating all data structures dynamically.
the entire hostname (including the delimiting dots but not a trailing dot) has a maximum of 253 ASCII characters
In general that is a good guideline, but when the standard (RFC1035) says there is an absolute limit, there is little value in going above that as it is likely that other systems won't be able to handle it. The added complexity of dynamic allocation is also an opportunity for bugs, like this one.
Again, this is especially silly if (as it appears to first glance) the bug is in a hostname validation function, and so flexible allocation could only ever be useful in the case of a hostname that must fail validation anyways.
In fact, it looks like if you get to the dynamic allocation section, it will fix the problem. One could argue that the whole problem stems from having a bug in a complex computation of buffer size to handle lots of different bits of data, rather than dynamically allocating the individual bits as needed.
struct hostent {
char *h_name; /* official name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses */
}
(edit) You may be totally right here, by the way.
In that specific case there are no aliases and exactly one IP address, but the buffer could still be too small (e.g. if caller-supplied with gethostbyname_r()).
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