Date: Sat, 12 Dec 1998 19:32:09 -0800 From: Don Lewis <Don.Lewis@tsc.tdk.com> To: Matthew Dillon <dillon@apollo.backplane.com>, Don Lewis <Don.Lewis@tsc.tdk.com> Cc: Peter Edwards <peter.edwards@isocor.ie>, Archie Cobbs <archie@whistle.com>, freebsd-current@FreeBSD.ORG Subject: Re: inetd: realloc/free bug Message-ID: <199812130332.TAA23232@salsa.gv.tsc.tdk.com> In-Reply-To: Matthew Dillon <dillon@apollo.backplane.com> "Re: inetd: realloc/free bug" (Dec 12, 5:58pm)
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On Dec 12, 5:58pm, Matthew Dillon wrote:
} Subject: Re: inetd: realloc/free bug
} :Your patch also doesn't eliminate all the race conditions. When
} :a signal handler is invoked, it blocks reception of the signal that
} :triggered it, but not the reception of other signals, so it is possible
}
} Sure it does. Look at the code. Line 410 or so of inetd.c
You appear to be correct.
} :Oh yeah, there is another race condition that I've never seen mentioned.
} :In the case of TCP services where we do something like
} : ctrl = accept(...);
} : pid = fork();
} : if (pid == 0) {
} : fiddle with fds
} : exec(...);
} : }
} : close(ctrl);
} :there is a problem if the child process runs, writes a bunch of data
} :to the socket and exits before the parent process executes the close().
} :If this happens, the close() in the parent can hang for an indefinite
} :period of time, until the client consumes the buffered data on the socket.
} :I fixed this in BIND 4.x a few years ago using a pipe to synchronize
}
} I'm not sure I follow. close() on a socket descriptor does not block.
In the case of BIND, close() blocks because SO_LINGER is set. As long
as nothing run from inetd does this, we're probably OK. The reason that
BIND uses SO_LINGER is:
/* kernels that map pages for IO end up failing if the pipe is full
* at exit and we take away the final buffer. this is really a kernel
* bug but it's harmless on systems that are not broken, so...
*/
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