[lxc-devel] [PATCH v3 4/4] uniformly nullify std fds

[Tycho Andersen]

On Wed, Jun 10, 2015 at 12:03:08PM +0000, Serge Hallyn wrote:
> Quoting Tycho Andersen (tycho.andersen at canonical.com):
> > In various places throughout the code, we want to "nullify" the std fds,
> > opening them to /dev/null or zero or so. Instead, let's unify this code and
> > do it in such a way that Coverity (probably) won't complain.
> > 
> > v2: use /dev/null for stdin as well
> > v3: add a comment about use of C's short circuiting
> > 
> > Reported-by: Coverity
> > Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> 
> Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>
> 
> Two comments below, please resend with my ack.
> 
> > ---
> >  src/lxc/bdev.c         |  8 ++------
> >  src/lxc/lxccontainer.c | 24 +++++++++++-------------
> >  src/lxc/monitor.c      |  8 ++------
> >  src/lxc/start.c        | 10 ++--------
> >  src/lxc/utils.c        | 16 ++++++++++++++++
> >  src/lxc/utils.h        |  1 +
> >  6 files changed, 34 insertions(+), 33 deletions(-)
> > 
> > diff --git a/src/lxc/bdev.c b/src/lxc/bdev.c
> > index 53465b1..520652c 100644
> > --- a/src/lxc/bdev.c
> > +++ b/src/lxc/bdev.c
> > @@ -224,12 +224,8 @@ static int do_mkfs(const char *path, const char *fstype)
> >  
> >  	// If the file is not a block device, we don't want mkfs to ask
> >  	// us about whether to proceed.
> > -	close(0);
> > -	close(1);
> > -	close(2);
> > -	open("/dev/zero", O_RDONLY);
> > -	open("/dev/null", O_RDWR);
> > -	open("/dev/null", O_RDWR);
> > +	if (null_stdfds() < 0)
> > +		exit(1);
> >  	execlp("mkfs", "mkfs", "-t", fstype, path, NULL);
> >  	exit(1);
> >  }
> > diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
> > index 445cc22..a0dd2a2 100644
> > --- a/src/lxc/lxccontainer.c
> > +++ b/src/lxc/lxccontainer.c
> > @@ -722,12 +722,10 @@ static bool do_lxcapi_start(struct lxc_container *c, int useinit, char * const a
> >  			return false;
> >  		}
> >  		lxc_check_inherited(conf, true, -1);
> > -		close(0);
> > -		close(1);
> > -		close(2);
> > -		open("/dev/zero", O_RDONLY);
> > -		open("/dev/null", O_RDWR);
> > -		open("/dev/null", O_RDWR);
> > +		if (null_stdfds() < 0) {
> > +			ERROR("failed to close fds");
> > +			return false;
> > +		}
> >  		setsid();
> >  	} else {
> >  		if (!am_single_threaded()) {
> > @@ -978,13 +976,13 @@ static bool create_run_template(struct lxc_container *c, char *tpath, bool quiet
> >  		char **newargv;
> >  		struct lxc_conf *conf = c->lxc_conf;
> >  
> > -		if (quiet) {
> > -			close(0);
> > -			close(1);
> > -			close(2);
> > -			open("/dev/zero", O_RDONLY);
> > -			open("/dev/null", O_RDWR);
> > -			open("/dev/null", O_RDWR);
> > +		/*
> > +		 * Here, we're taking advantage of C's short circuiting of
> > +		 * conditions: we should only fail if quiet is set and
> > +		 * null_stdfds fails.
> > +		 */
> 
> No, please drop that comment ^.
> 
> > +		if (quiet && null_stdfds() < 0) {
> > +			exit(1);
> >  		}
> >  
> >  		src = c->lxc_conf->rootfs.path;
> > diff --git a/src/lxc/monitor.c b/src/lxc/monitor.c
> > index 0e56f75..144b16e 100644
> > --- a/src/lxc/monitor.c
> > +++ b/src/lxc/monitor.c
> > @@ -329,12 +329,8 @@ int lxc_monitord_spawn(const char *lxcpath)
> >  		exit(EXIT_FAILURE);
> >  	}
> >  	lxc_check_inherited(NULL, true, pipefd[1]);
> > -	close(0);
> > -	close(1);
> > -	close(2);
> > -	open("/dev/null", O_RDONLY);
> > -	open("/dev/null", O_RDWR);
> > -	open("/dev/null", O_RDWR);
> > +	if (null_stdfds() < 0)
> > +		exit(EXIT_FAILURE);
> >  	close(pipefd[0]);
> >  	sprintf(pipefd_str, "%d", pipefd[1]);
> >  	execvp(args[0], args);
> > diff --git a/src/lxc/start.c b/src/lxc/start.c
> > index 71cd9ef..6eded61 100644
> > --- a/src/lxc/start.c
> > +++ b/src/lxc/start.c
> > @@ -762,14 +762,8 @@ static int do_start(void *data)
> >  
> >  	close(handler->sigfd);
> >  
> > -	if (handler->backgrounded) {
> > -		close(0);
> > -		close(1);
> > -		close(2);
> > -		open("/dev/zero", O_RDONLY);
> > -		open("/dev/null", O_RDWR);
> > -		open("/dev/null", O_RDWR);
> > -	}
> > +	if (handler->backgrounded && null_stdfds() < 0)
> > +		goto out_warn_father;
> >  
> >  	/* after this call, we are in error because this
> >  	 * ops should not return as it execs */
> > diff --git a/src/lxc/utils.c b/src/lxc/utils.c
> > index 467bc1b..42dd38f 100644
> > --- a/src/lxc/utils.c
> > +++ b/src/lxc/utils.c
> > @@ -1445,3 +1445,19 @@ domount:
> >  	INFO("Mounted /proc in container for security transition");
> >  	return 1;
> >  }
> > +
> > +int null_stdfds(void)
> > +{
> > +	int fd;
> > +
> > +	fd = open("/dev/null", O_RDWR);
> > +	if (fd < 0)
> > +		return -1;
> > +
> > +	dup2(fd, 0);
> > +	dup2(fd, 1);
> 
> Just to make sure, have you tried a package or ppa build to make
> sure that the lack of error checking doesn't upset the build
> system?

I haven't, but coverity probably complains and since that's the whole
point of this dance I'll resend with error checks.

Tycho

> > +	dup2(fd, 2);
> > +	close(fd);
> > +
> > +	return 0;
> > +}
> > diff --git a/src/lxc/utils.h b/src/lxc/utils.h
> > index 6bd05e0..ee12dde 100644
> > --- a/src/lxc/utils.h
> > +++ b/src/lxc/utils.h
> > @@ -280,4 +280,5 @@ int is_dir(const char *path);
> >  char *get_template_path(const char *t);
> >  int setproctitle(char *title);
> >  int mount_proc_if_needed(const char *rootfs);
> > +int null_stdfds(void);
> >  #endif /* __LXC_UTILS_H */
> > -- 
> > 2.1.4
> > 
> > _______________________________________________
> > lxc-devel mailing list
> > lxc-devel at lists.linuxcontainers.org
> > http://lists.linuxcontainers.org/listinfo/lxc-devel
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