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-rw-r--r--Documentation/lguest/lguest.c73
1 files changed, 65 insertions, 8 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index dc73bc54..d9da7e1 100644
--- 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();
}