s3: util: Do not take over stderr when there is no log file

Enterprise / Samba - Paulo Alcantara [paulo.ac] - 17 August 2018 23:32 EDT

In case we don't have either a /var/log/samba directory, or pass a non-existent log directory through '-l' option, all commands that are daemonized with '-D' option hang when executed within a subshell.

An example on how to trigger that:

# rm -r /var/log/samba # s=$(nmbd -D -s /etc/samba/smb.conf -l /foo123) (never returns)

So, when the above command is executed within a subshell the following happens:

(a) Parent shell creates a pipe, sets write side of it to fd 1 (stdout), call read() on read-side fd, forks off a new child process and then executes nmbd in it. (b) nmbd sets up initial logging to go through fd 1 (stdout) by calling setup_logging(..., DEBUG_DEFAULT_STDOUT). 'state.fd' is now set to 1. (c) reopen_logs() is called by the first time which then calls reopen_logs_internal() (d) in reopen_logs_internal(), it attempts to create log.nmbd file in /foo123 directory and fails because directory doesn't exist. (e) Regardless whether the log file was created or not, it calls dup2(state.fd, 2) which dups fd 1 into fd 2. (f) At some point, fd 0 and 1 are closed and set to /dev/null

The problem with that is because parent shell in (a) is still blocked in read() call and the new write side of the pipe is now fd 2 -- after dup2() in (e) -- and remains unclosed.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13578

41aa55f4923 s3: util: Do not take over stderr when there is no log file
lib/util/debug.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

Upstream: gitweb.samba.org


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