Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input

[pandora-kernel.git] / Documentation / lguest / lguest.c

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index dc73bc5..d9da7e1 100644 (file)
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -39,6 +39,9 @@
 #include <limits.h>
 #include <stddef.h>
 #include <signal.h>
+#include <pwd.h>
+#include <grp.h>
+
 #include <linux/virtio_config.h>
 #include <linux/virtio_net.h>
 #include <linux/virtio_blk.h>
@@ -298,20 +301,27 @@ static void *map_zeroed_pages(unsigned int num)
 
        /*
         * We use a private mapping (ie. if we write to the page, it will be
-        * copied).
+        * copied). We allocate an extra two pages PROT_NONE to act as guard
+        * pages against read/write attempts that exceed allocated space.
         */
-       addr = mmap(NULL, getpagesize() * num,
-                   PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, fd, 0);
+       addr = mmap(NULL, getpagesize() * (num+2),
+                   PROT_NONE, MAP_PRIVATE, fd, 0);
+
        if (addr == MAP_FAILED)
                err(1, "Mmapping %u pages of /dev/zero", num);
 
+       if (mprotect(addr + getpagesize(), getpagesize() * num,
+                    PROT_READ|PROT_WRITE) == -1)
+               err(1, "mprotect rw %u pages failed", num);
+
        /*
         * One neat mmap feature is that you can close the fd, and it
         * stays mapped.
         */
        close(fd);
 
-       return addr;
+       /* Return address after PROT_NONE page */
+       return addr + getpagesize();
 }
 
 /* Get some more pages for a device. */
@@ -343,7 +353,7 @@ static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
         * done to it.  This allows us to share untouched memory between
         * Guests.
         */
-       if (mmap(addr, len, PROT_READ|PROT_WRITE|PROT_EXEC,
+       if (mmap(addr, len, PROT_READ|PROT_WRITE,
                 MAP_FIXED|MAP_PRIVATE, fd, offset) != MAP_FAILED)
                return;
 
@@ -573,10 +583,10 @@ static void *_check_pointer(unsigned long addr, unsigned int size,
                            unsigned int line)
 {
        /*
-        * We have to separately check addr and addr+size, because size could
-        * be huge and addr + size might wrap around.
+        * Check if the requested address and size exceeds the allocated memory,
+        * or addr + size wraps around.
         */
-       if (addr >= guest_limit || addr + size >= guest_limit)
+       if ((addr + size) > guest_limit || (addr + size) < addr)
                errx(1, "%s:%i: Invalid address %#lx", __FILE__, line, addr);
        /*
         * We return a pointer for the caller's convenience, now we know it's
@@ -1872,6 +1882,8 @@ static struct option opts[] = {
        { "block", 1, NULL, 'b' },
        { "rng", 0, NULL, 'r' },
        { "initrd", 1, NULL, 'i' },
+       { "username", 1, NULL, 'u' },
+       { "chroot", 1, NULL, 'c' },
        { NULL },
 };
 static void usage(void)
@@ -1894,6 +1906,12 @@ int main(int argc, char *argv[])
        /* If they specify an initrd file to load. */
        const char *initrd_name = NULL;
 
+       /* Password structure for initgroups/setres[gu]id */
+       struct passwd *user_details = NULL;
+
+       /* Directory to chroot to */
+       char *chroot_path = NULL;
+
        /* Save the args: we "reboot" by execing ourselves again. */
        main_args = argv;
 
@@ -1950,6 +1968,14 @@ int main(int argc, char *argv[])
                case 'i':
                        initrd_name = optarg;
                        break;
+               case 'u':
+                       user_details = getpwnam(optarg);
+                       if (!user_details)
+                               err(1, "getpwnam failed, incorrect username?");
+                       break;
+               case 'c':
+                       chroot_path = optarg;
+                       break;
                default:
                        warnx("Unknown argument %s", argv[optind]);
                        usage();
@@ -2021,6 +2047,37 @@ int main(int argc, char *argv[])
        /* If we exit via err(), this kills all the threads, restores tty. */
        atexit(cleanup_devices);
 
+       /* If requested, chroot to a directory */
+       if (chroot_path) {
+               if (chroot(chroot_path) != 0)
+                       err(1, "chroot(\"%s\") failed", chroot_path);
+
+               if (chdir("/") != 0)
+                       err(1, "chdir(\"/\") failed");
+
+               verbose("chroot done\n");
+       }
+
+       /* If requested, drop privileges */
+       if (user_details) {
+               uid_t u;
+               gid_t g;
+
+               u = user_details->pw_uid;
+               g = user_details->pw_gid;
+
+               if (initgroups(user_details->pw_name, g) != 0)
+                       err(1, "initgroups failed");
+
+               if (setresgid(g, g, g) != 0)
+                       err(1, "setresgid failed");
+
+               if (setresuid(u, u, u) != 0)
+                       err(1, "setresuid failed");
+
+               verbose("Dropping privileges completed\n");
+       }
+
        /* Finally, run the Guest.  This doesn't return. */
        run_guest();
 }