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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Adhemerval Zanella via Libc-alpha Reply-To: Adhemerval Zanella Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" On 29/06/2020 11:30, Andreas Schwab wrote: > Properly serialize the access to the global state shared between the > syslog functions, to avoid races in multithreaded processes. Protect a > local allocation in the __vsyslog_internal function from leaking during > cancellation. LGTM, thanks. As a side note, I think we could simplify this code a bit if we just define syslog as non-cancellable (since POSIX states it is a 'may' entrypoint) and to remove the internal 'syslog' call on __vsyslog_internal. Former would allow to just call __pthread_setcancelstate / __pthread_setcancelstate on each required symbol and former would allow to move the lock/unlock out of __vsyslog_internal. We might still check the NO_SIGPIPE necessity (as least Linux explicit sets it, not sure if Hurd requires it). Reviewed-by: Adhemerval Zanella > --- > misc/syslog.c | 44 ++++++++++++++++++++++++++++---------------- > 1 file changed, 28 insertions(+), 16 deletions(-) > > diff --git a/misc/syslog.c b/misc/syslog.c > index fd6537edf6..2cc63ef287 100644 > --- a/misc/syslog.c > +++ b/misc/syslog.c > @@ -91,14 +91,20 @@ struct cleanup_arg > static void > cancel_handler (void *ptr) > { > -#ifndef NO_SIGPIPE > /* Restore the old signal handler. */ > struct cleanup_arg *clarg = (struct cleanup_arg *) ptr; > > - if (clarg != NULL && clarg->oldaction != NULL) > - __sigaction (SIGPIPE, clarg->oldaction, NULL); > + if (clarg != NULL) > + { > +#ifndef NO_SIGPIPE > + if (clarg->oldaction != NULL) > + __sigaction (SIGPIPE, clarg->oldaction, NULL); > #endif > > + /* Free the memstream buffer, */ > + free (clarg->buf); > + } > + > /* Free the lock. */ > __libc_lock_unlock (syslog_lock); > } Ok. > @@ -169,9 +175,17 @@ __vsyslog_internal(int pri, const char *fmt, va_list ap, > pri &= LOG_PRIMASK|LOG_FACMASK; > } > > + /* Prepare for multiple users. We have to take care: most > + syscalls we are using are cancellation points. */ > + struct cleanup_arg clarg; > + clarg.buf = NULL; > + clarg.oldaction = NULL; > + __libc_cleanup_push (cancel_handler, &clarg); > + __libc_lock_lock (syslog_lock); > + > /* Check priority against setlogmask values. */ > if ((LOG_MASK (LOG_PRI (pri)) & LogMask) == 0) > - return; > + goto out; > > /* Set default facility if none specified. */ > if ((pri & LOG_FACMASK) == 0) Ok. > @@ -235,6 +249,9 @@ __vsyslog_internal(int pri, const char *fmt, va_list ap, > /* Close the memory stream; this will finalize the data > into a malloc'd buffer in BUF. */ > fclose (f); > + > + /* Tell the cancellation handler to free this buffer. */ > + clarg.buf = buf; > } > > /* Output to stderr if requested. */ Ok. > @@ -252,22 +269,10 @@ __vsyslog_internal(int pri, const char *fmt, va_list ap, > v->iov_len = 1; > } > > - __libc_cleanup_push (free, buf == failbuf ? NULL : buf); > - > /* writev is a cancellation point. */ > (void)__writev(STDERR_FILENO, iov, v - iov + 1); > - > - __libc_cleanup_pop (0); > } > > - /* Prepare for multiple users. We have to take care: open and > - write are cancellation points. */ > - struct cleanup_arg clarg; > - clarg.buf = buf; > - clarg.oldaction = NULL; > - __libc_cleanup_push (cancel_handler, &clarg); > - __libc_lock_lock (syslog_lock); > - > #ifndef NO_SIGPIPE > /* Prepare for a broken connection. */ > memset (&action, 0, sizeof (action)); Ok. > @@ -320,6 +325,7 @@ __vsyslog_internal(int pri, const char *fmt, va_list ap, > __sigaction (SIGPIPE, &oldaction, (struct sigaction *) NULL); > #endif > > + out: > /* End of critical section. */ > __libc_cleanup_pop (0); > __libc_lock_unlock (syslog_lock); > @@ -430,8 +436,14 @@ setlogmask (int pmask) > { > int omask; > > + /* Protect against multiple users. */ > + __libc_lock_lock (syslog_lock); > + > omask = LogMask; > if (pmask != 0) > LogMask = pmask; > + > + __libc_lock_unlock (syslog_lock); > + > return (omask); > } > Ok.