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Message-ID: <20130320124125.GL19010@port70.net>
Date: Wed, 20 Mar 2013 13:41:26 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: Weird bug in syslog
* William Haddon <william@...donthethird.net> [2013-03-19 15:32:35 -0400]:
> I noticed seg-faults and other weird behavior when using the syslog()
> function with large messages. I've attached the simplest test program
> that reproduces the problem. I've observed it to break on 0.9.9 on i386
> and current git on x86_64. The problem seems to be that although the
> syslog function successfully truncates its input to 256 bytes, it
> passes the size of the un-truncated form to the sendto() call because
> snprintf returns the number of bytes that would be written if
> truncation did not occur. Fixing syslog to check if truncation occurred
> seems to fix the problem. I've attached the patch that does this.
i can confirm this
> Report the correct length of the datagram to the kernel to fix strange behavior
> in the syslog function.
> --- musl-0.9.9/src/misc/syslog.c
> +++ src/src/misc/syslog.c
> @@ -90,9 +90,11 @@
> priority, timebuf,
> log_ident ? log_ident : "",
> "["+!pid, pid, "]"+!pid);
> + if (l > sizeof buf) l = sizeof buf - 1;
l >= sizeof buf
(it is not correct when l<0 but that snprintf cannot fail)
> l2 = vsnprintf(buf+l, sizeof buf - l, message, ap);
> if (l2 >= 0) {
> l += l2;
these are int values
maybe we should care about overflow
(eg making l size_t works)
> + if (l > sizeof buf) l = sizeof buf - 1;
l >= sizeof buf
> if (buf[l-1] != '\n') buf[l++] = '\n';
> sendto(log_fd, buf, l, 0, (void *)&log_addr, 11);
> }
>
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