lxc-usernsexec: reopen fds 0,1,2 separately

lxc-usernsexec was using fd 0 and reopening it as 0,1,2 for
the new task.  If doing "lxc-usernsexec .. < script" this
will corrupt the file 'script'.

Reported-by: Fiedler Roman <Roman.Fiedler@ait.ac.at>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

diff --git a/src/lxc/lxc_usernsexec.c b/src/lxc/lxc_usernsexec.c
index 19049ffccccdfcf8aac0743afd00f6b3de2d6ace..99927cf50eefaba4e3d7f0ccffa0a1993330f812 100644 (file)
--- a/src/lxc/lxc_usernsexec.c
+++ b/src/lxc/lxc_usernsexec.c
@@ -74,12 +74,16 @@ static void usage(const char *name)
        exit(1);
 }
 
-static void opentty(const char * tty) {
-       int i, fd, flags;
+static void opentty(const char * tty, int which) {
+       int fd, flags;
+
+       if (tty[0] == '\0')
+               return;
 
        fd = open(tty, O_RDWR | O_NONBLOCK);
        if (fd == -1) {
                printf("WARN: could not reopen tty: %s\n", strerror(errno));
+               close(which);
                return;
        }
 
@@ -87,16 +91,15 @@ static void opentty(const char * tty) {
        flags &= ~O_NONBLOCK;
        if (fcntl(fd, F_SETFL, flags) < 0) {
                printf("WARN: could not set fd flags: %s\n", strerror(errno));
+               close(which);
                return;
        }
 
-       for (i = 0; i < fd; i++)
-               close(i);
-       for (i = 0; i < 3; i++)
-               if (fd != i)
-                       dup2(fd, i);
-       if (fd >= 3)
+       close(which);
+       if (fd != which) {
+               dup2(fd, which);
                close(fd);
+       }
 }
 // Code copy end
 
@@ -265,7 +268,7 @@ int main(int argc, char *argv[])
 {
        int c;
        unsigned long flags = CLONE_NEWUSER | CLONE_NEWNS;
-       char ttyname[256];
+       char ttyname0[256], ttyname1[256], ttyname2[256];
        int status;
        int ret;
        int pid;
@@ -274,12 +277,24 @@ int main(int argc, char *argv[])
        int pipe1[2],  // child tells parent it has unshared
            pipe2[2];  // parent tells child it is mapped and may proceed
 
-       memset(ttyname, '\0', sizeof(ttyname));
-       ret = readlink("/proc/self/fd/0", ttyname, sizeof(ttyname));
+       memset(ttyname0, '\0', sizeof(ttyname0));
+       memset(ttyname1, '\0', sizeof(ttyname1));
+       memset(ttyname2, '\0', sizeof(ttyname2));
+       ret = readlink("/proc/self/fd/0", ttyname0, sizeof(ttyname0));
        if (ret < 0) {
-               perror("readlink on fd 0");
+               perror("unable to open stdin.");
                exit(1);
        }
+       ret = readlink("/proc/self/fd/1", ttyname1, sizeof(ttyname1));
+       if (ret < 0) {
+               printf("Warning: unable to open stdout, continuing.");
+               memset(ttyname1, '\0', sizeof(ttyname1));
+       }
+       ret = readlink("/proc/self/fd/2", ttyname2, sizeof(ttyname2));
+       if (ret < 0) {
+               printf("Warning: unable to open stderr, continueing.");
+               memset(ttyname2, '\0', sizeof(ttyname2));
+       }
 
        lxc_list_init(&active_map);
 
@@ -315,7 +330,9 @@ int main(int argc, char *argv[])
 
                close(pipe1[0]);
                close(pipe2[1]);
-               opentty(ttyname);
+               opentty(ttyname0, 0);
+               opentty(ttyname1, 1);
+               opentty(ttyname2, 2);
 
                ret = unshare(flags);
                if (ret < 0) {