On 2/20/19 9:20 PM, Warner Losh wrote: > On Wed, Feb 20, 2019, 9:59 PM Enji Cooper <yaneurab...@gmail.com wrote: > >> >>> On Feb 20, 2019, at 5:17 PM, Bruce Evans <b...@optusnet.com.au> wrote: >>> >>> On Wed, 20 Feb 2019, David Bright wrote: >>> >>>> Log: >>>> Complete fix for CID 1007454, CID 1007453: Resource leak in newsyslog >>>> >>>> The result of a strdup() was stored in a global variable and not freed >>>> before program exit. This is a follow-up to r343906. That change >>> >>> This was an especially large bug in Coverity. Understanding that exit(3) >>> exits is about the first thing to understand for a checker. >>> >>> Now it is also a style bug in the source code. >>> >>>> attempted to plug these resource leaks but managed to miss a code path >>>> on which the leak still occurs. Plug the leak on that path, too. >>> >>>> Modified: head/usr.sbin/newsyslog/newsyslog.c >>>> >> ============================================================================== >>>> --- head/usr.sbin/newsyslog/newsyslog.c Wed Feb 20 21:24:56 2019 >> (r344388) >>>> +++ head/usr.sbin/newsyslog/newsyslog.c Wed Feb 20 22:05:44 2019 >> (r344389) >>>> @@ -793,6 +793,9 @@ usage(void) >>>> fprintf(stderr, >>>> "usage: newsyslog [-CFNPnrsv] [-a directory] [-d directory] >> [-f config_file]\n" >>>> " [-S pidfile] [-t timefmt] [[-R tagname] file >> ...]\n"); >>>> + /* Free global dynamically-allocated storage. */ >>>> + free(timefnamefmt); >>>> + free(requestor); >>>> exit(1); >>>> } >>> >>> There was no leak here. exit(3) frees storage much more finally than >>> free(3). >>> >>> It is especially obvious that there is no leak here, since the exit() is >>> 1-2 lines later than the frees. >>> >>> In theory, exit() might fail because it tries to allocate 100 MB more >>> storage but wouldn't fail if 100 bytes are freed here (applications can >>> easily do this foot shooting by allocating without freeing in atexit() >>> destructors). In practice, even allocation failures "can't happen", >>> except in programs that use setrlimit followed but foot shooting to test >>> the limits. setrlimit is now broken for this purpose, since it doesn't >>> limit allocations done using mmap() instead of break(), and malloc() now >>> uses mmap(). >>> >>> If coverity understood this and wanted to spam you with warnings, then it >>> would not warn about this, but would warn about more important things >> like >>> failure to fflush() or fclose() or check for or handle errors for all >>> open streams before calling exit(). Also, if all callers of usage() are >>> not understood, for failures to switch stderr to unbuffered mode before >>> using it in usage(). >>> >>> The error reporting is even harder to do if stderr is not available. >>> Windowing systems and even curses need to do lots more cleanup _before_ >>> exit() and it may be difficult to clean up enough to print error messages >>> using the windowing system. >> >> I agree with Bruce. Items like these should be ignored in the Coverity UI >> as false positives with reasoning, like “global variables; freed on exit”. >> >> As others have noted in past mailing threads, freeing variables on exit >> can cause applications to hang for a period of time, while the memory is >> being reclaimed. I think it’s best to ignore these kinds of allocations on >> exit to avoid introducing unnecessary complexity in the program, as they’re >> benign issues. >> > > > It's been a long running debate since 92 or so when purify came out and > this problem started to be found. In the last 25 years the question hasn't > been settled. I tend to think it's a waste of time, though I get that > issues like this create a lot of false positives.
I'm +1 on Bruce's point on this. I find it similar to the recent spate of adding pointless '__dead2' annotations to usage functions that unconditionally call exit() (and thus are already inferred as __dead2 by any compiler written in this millenium) -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"