Re: [PATCH 1/2] kissattach: Add support for pty symlinking

[walter harms <wharms@bfs.de>]

Am 28.06.2015 05:04, schrieb me@vk4msl.yi.org:
> From: Stuart Longland <stuartl@longlandclan.yi.org>
> 
> This patch adds abilities for symlinking of dynamically allocated slave
> PTY interfaces to kissattach.  This enables other services to make use
> of these PTYs without manually editing their configuration files to
> point to the dynamically allocated PTY.
> 
> In addition, the patch includes the ability to change the ownership and
> permissions on the allocated PTY, allowing an unpriviged process to make
> use of it.
> ---
>  kiss/kissattach.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 103 insertions(+), 7 deletions(-)
> 
> diff --git a/kiss/kissattach.c b/kiss/kissattach.c
> index e30ed05..a872d0a 100644
> --- a/kiss/kissattach.c
> +++ b/kiss/kissattach.c
> @@ -18,6 +18,9 @@
>  #include <sys/socket.h>
>  #include <sys/ioctl.h>
>  
> +#include <pwd.h>
> +#include <grp.h>
> +
>  #include <net/if.h>
>  #include <netax25/ax25.h>
>  #include <netrose/rose.h>
> @@ -32,6 +35,8 @@
>  #define N_6PACK 7	/* This is valid for all architectures in 2.2.x */
>  #endif
>  
> +#define PTMX_TTY	"/dev/ptmx"
> +
>  static char *callsign;
>  static int  speed;
>  static int  mtu;
> @@ -42,6 +47,7 @@ static char *portname;
>  static char *inetaddr;
>  static int allow_broadcast;
>  static int i_am_unix98_pty_master;		/* unix98 ptmx support */
> +static int symlink_pty = 0;
>  
>  static char *kiss_basename(char *s)
>  {
> @@ -58,6 +64,8 @@ static void terminate(int sig)
>  
>  	if (!i_am_unix98_pty_master)
>  		tty_unlock(kttyname);
> +	else if (symlink_pty)
> +		unlink(kttyname);
>  
>  	exit(0);
>  }
> @@ -214,7 +222,8 @@ static int startiface(char *dev, struct hostent *hp)
>  
>  static void usage(void)
>  {
> -	fprintf(stderr, "usage: %s [-b] [-l] [-m mtu] [-v] tty port [inetaddr]\n", progname);
> +	fprintf(stderr, "usage: %s [-b] [-l] [-m mtu] [-v] [-o user:group] [-p mode] tty port [inetaddr]\n",
> +			progname);
>  }
>  
>  int main(int argc, char *argv[])
> @@ -227,12 +236,18 @@ int main(int argc, char *argv[])
>  				* the client has to use */
>  	struct hostent *hp = NULL;
>  
> +	/* Name of the user and group who will "own" the pty */
> +	char* pty_owner_user = NULL;
> +	char* pty_owner_group = NULL;
> +	/* Mode for pty: if 0; use defaults */
> +	mode_t pty_mode = 0;
> +
>  	progname = kiss_basename(argv[0]);
>  
>  	if (!strcmp(progname, "spattach"))
>  		disc = N_6PACK;
>  
> -	while ((fd = getopt(argc, argv, "b6i:lm:v")) != -1) {
> +	while ((fd = getopt(argc, argv, "b6i:lm:o:p:v")) != -1) {
>  		switch (fd) {
>  		case '6':
>  			disc = N_6PACK;
> @@ -250,9 +265,24 @@ int main(int argc, char *argv[])
>  		case 'm':
>  			if ((mtu = atoi(optarg)) <= 0) {
>  				fprintf(stderr, "%s: invalid mtu size - %s\n", progname, optarg);
> -				return 1;
> +		case 'o':
> +			/* Change the owner of the pty */
> +			{
> +				char* colon = index(optarg,':');
> +				if (colon) {
> +					pty_owner_user = optarg;
> +					pty_owner_group = colon + 1;
> +					*colon = 0;
> +				} else {
> +					fprintf(stderr, "%s: Must specify user:group\n", progname);
> +					return 1;
> +				}
>  			}
>  			break;
> +		case 'p':
> +			/* Change the permissions (mode) of the pty */
> +			pty_mode = (mode_t)strtoul(optarg, NULL, 8);
> +			break;
>  		case 'v':
>  			printf("%s: %s\n", progname, VERSION);
>  			return 0;

hi Stuart,
what was the model for you cli ? i was looking at 'install' and it uses
-g group
-o owner
-m mode


> @@ -278,8 +308,17 @@ int main(int argc, char *argv[])
>  	if (argc-1 >= optind && !inetaddr)
>  		inetaddr = argv[optind];
>  
> -	if (!strcmp("/dev/ptmx", kttyname))
> +	if (!strcmp(PTMX_TTY, kttyname)) {
> +		i_am_unix98_pty_master = 1;
> +	} else if (strstr(kttyname, "pty:") == kttyname) {
> +		/*
> +		 * If the path starts with pty:, then create a
> +		 * new pty (Unix98 style) and make a symlink to it
> +		 */
>  		i_am_unix98_pty_master = 1;
> +		kttyname = index(kttyname, ':') + 1;
> +		symlink_pty = 1;
> +	}
>  
>  	if (!i_am_unix98_pty_master) {
>  		if (tty_is_locked(kttyname)) {
> @@ -296,7 +335,7 @@ int main(int argc, char *argv[])
>  		return 1;
>  	}
>  
> -	if ((fd = open(kttyname, O_RDONLY | O_NONBLOCK)) == -1) {
> +	if ((fd = open((symlink_pty ? PTMX_TTY : kttyname), O_RDONLY | O_NONBLOCK)) == -1) {
>  		if (errno == ENOENT) {
>  			fprintf(stderr, "%s: Cannot find serial device %s, no such file or directory.\n", progname, kttyname);
>  		} else {
> @@ -353,12 +392,69 @@ int main(int argc, char *argv[])
>  
>  	printf("AX.25 port %s bound to device %s\n", portname, dev);
>  	if (i_am_unix98_pty_master) {
> -		/* Users await the slave pty to be referenced in the 3d line */
> -		printf("Awaiting client connects on\n%s\n", namepts);
> +		/* Are we being asked to chown? */
> +		if (pty_owner_user) {
> +			/* Look up the user */
> +			struct passwd user;
> +			struct passwd* user_ptr = NULL;
> +			struct group grp;
> +			struct group* grp_ptr = NULL;
> +			char buffer[512];
> +			int err = getpwnam_r(pty_owner_user, &user,
> +				buffer, sizeof(buffer)-1, &user_ptr);

why _r ? any need to make it thread safe ?

just my 2 cents,
re,
 wh

> +			if (err) {
> +				fprintf(stderr,
> +					"Failed to look up user: %s (%d)\n",
> +					strerror(err), err);
> +				return 1;
> +			}
> +
> +			err = getgrnam_r(pty_owner_group, &grp,
> +				buffer, sizeof(buffer)-1, &grp_ptr);
> +			if (err) {
> +				fprintf(stderr,
> +					"Failed to look up group: %s (%d)\n",
> +					strerror(err), err);
> +				return 1;
> +			}
> +
> +			if (user_ptr && grp_ptr &&
> +					chown(namepts, user_ptr->pw_uid,
> +						grp_ptr->gr_gid)) {
> +				fprintf(stderr,
> +					"Failed to change ownership: %s (%d)\n",
> +					strerror(errno), errno);
> +				return 1;
> +			}
> +		}
> +
> +		/* Are we being asked to chmod? */
> +		if (pty_mode) {
> +			if (chmod(namepts, pty_mode)) {
> +				fprintf(stderr,
> +					"Failed to change mode: %s (%d)\n",
> +					strerror(errno), errno);
> +			}
> +		}
> +
> +		if (symlink_pty) {
> +			/* Create the symlink */
> +			if (symlink(namepts, kttyname)) {
> +				fprintf(stderr,
> +					"Failed to symlink PTY %s to %s: %s (%d)\n",
> +					kttyname, namepts, strerror(errno), errno);
> +				return 1;
> +			}
> +		} else {
> +			/* Users await the slave pty to be referenced in the 3d line */
> +			printf("Awaiting client connects on\n%s\n", namepts);
> +		}
>  	}
>  	if (logging) {
>  		openlog(progname, LOG_PID, LOG_DAEMON);
>  		syslog(LOG_INFO, "AX.25 port %s bound to device %s%s%s\n", portname, dev, (i_am_unix98_pty_master ? " with slave pty " : ""), (i_am_unix98_pty_master ? namepts : ""));
> +		if (symlink_pty)
> +			syslog(LOG_INFO, "Slave pty %s is symlinked to %s.", namepts, kttyname);
>  
>  	}
>