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There are two problems with lookup_common() and therefore selabel_lookup() and related functions that this patch fixes: 1) A race with the lazy compilation of regexes. Since the struct regex_data is allocated and assigned immediately to the parent struct spec, it's possible for a second thread to see that this pointer is non-NULL before the regex compilation has finished. This typically results in a -1 return from selabel_lookup() with ENOENT as errno. This is fixed by adding synchronization in compile_regex(). 2) A race with PCRE2 regex_match(). A struct pcre2_match_data is created once and used for all regex matches for a given regex. This is problematic if two threads are attempting to evaluate the same regex simultaneously. This typically results in a successful return from selabel_lookup() but with an erroneous selabel. This is fixed by adding a pthread_mutex within regex_match() for PCRE2. Note, on my system, creating new matchdata takes roughly an order of magnitude more time than locking a non-contended pthread_mutex. I don't believe programs will have enough contention on this lock to justify that cost. Bug: 63861738 Test: ueventd unit tests Change-Id: I13bf782d81d0a0b896d444e396f307ad0dbacb6a |
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