[Bug 2688] New: Long log messages to stderr missing newlines

[bugzilla-daemon at bugzilla.mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=2688

            Bug ID: 2688
           Summary: Long log messages to stderr missing newlines
           Product: Portable OpenSSH
           Version: 7.4p1
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: minor
          Priority: P5
         Component: sshd
          Assignee: unassigned-bugs at mindrot.org
          Reporter: brian.dyson at cox.net

When logging to standard error (via -e) or to log file (via -E
<logfile>), long log messages do not end with a newline.

Problem occurs in log.c, line 456 in OpenSSH 7.4p1.

The snprintf() call attempts to copy fmtbuf and "\r\n" into msgbuf.
However, fmtbuf and msgbuf are the same size (MSGBUFSIZ, nominally 1024
bytes). When fmtbuf is completely filled (due to long log message),
then the snprintf() simply copies fmtbuf and ignores the "\r\n".

This was observed when testing certificate-based logins at LogLevel
DEBUG3.

For example, 3 logs messages appear on one line like this (with ...
replacing long OpenSSH certificate public key):

debug2: user_key_allowed: check options: 'ssh-rsa-cert-v01 at openssh.com
AAAA...debug2: user_key_allowed: advance: 'AAAA...debug2: key not found

Notice multiple debug2 messages all on the same line. Each log line
should with with a newline character.

Suggested Fix

Since the intent is to append "\r\n" to fmtbuf before writing to
stderr, maybe it would be better to make that intent clearer using
strlcat() rather than snprintf().

msgbuf[0] = '\0';
(void)strlcat(msgbuf, fmtbuf, sizeof msgbuf  - 2);
(void)strlcat(msgbuf, "\r\n", sizeof msgbuf );

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