Stephen Smoogen writes:
I am trying to figure out the logic of this section: ``` static char * lastUname = NULL; // So lastUname is NULL static uid_t lastUid; if (!thisUname) {lastUname = rfree(lastUname); // lastUname should still be NULL and we are freeing NULL and setting itself back to NULL.return -1; ```I expect this is where I am not understanding something basic in C from too many years in non-pointer land. I looked at the change of these lines and they date back to this commit.
This is a fairly common kind of simple caching to avoid expensive username/userid and groupname/groupid lookups by caching the last one. This code is expecting that it will be called, repeatedly, to look up the same user/group, so it caches the results of the last lookup, and returns it. Most of the files in a binary rpm would typically have the same uid gid owner, so these functions are expected to be called with the same values each time.
Which now get cached in static variables. This worked great while everything was single-threaded.
Now, if you have two execution threads going step by step right here, and both of them passed in a null pointer, both of them will run this, and both of them will `free` the same pointer. Fail.
This `static` usage pattern is inherently thread unsafe.
The entries for __thread I found come in around 2019. Did you have a bugzilla or a report on <URL:https://github.com/rpm-software- management/rpm/>https://github.com/rpm-software-management/rpm/ which I can add anything I find?and most date back from 2013. --
https://github.com/rpm-software-management/rpm/issues/2826
Attachment:
pgphOhqtJH6BS.pgp
Description: PGP signature
-- _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue
