[Lguest] Patches...

[Rusty Russell]

Hi Philip,

   There was some whitespace damage so I ended up reworking and splitting
your patches.  Mainly flipped it to kernel-style coding, and added some
commentry (some extracted from our email conversation).

Here they are, for your ack/Signed-off-by.

Thanks!
Rusty.

Subject: lguest: example launcher to use guard pages, drop PROT_EXEC, fix limit logic
From: Philip Sanderson <philip.k.sanderson at gmail.com>

PROT_EXEC seems to be completely unnecessary (as the lguest binary
never executes there), and will allow it to work with SELinux (and
more importantly, PaX :-) as they can/do forbid writable and
executable mappings.

Also, map PROT_NONE guard pages at start and end of guest memory for extra
paranoia.

I changed the length check to addr + size > guest_limit because >= is wrong
(addr of 0, size of getpagesize() with a guest_limit of getpagesize() would
false positive).

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -298,10 +298,12 @@ static void *map_zeroed_pages(unsigned i
 
 	/*
 	 * 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 invalid 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);
 
@@ -343,7 +345,7 @@ static void map_at(int fd, void *addr, u
 	 * 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 +575,10 @@ static void *_check_pointer(unsigned lon
 			    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


Subject: lguest: --username and --chroot options
From: Philip Sanderson <philip.k.sanderson at gmail.com>

I've attached a patch which implements dropping to privileges
and chrooting to a directory.

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff -ur linux-2.6.35.8-orig/Documentation/lguest/lguest.c
linux-2.6.35.8/Documentation/lguest/lguest.c

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
--- 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>
@@ -1874,6 +1877,8 @@ 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)
@@ -1896,6 +1901,12 @@ 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;
 
@@ -1952,6 +1963,14 @@ 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();


Subject: lguest: document --rng in example Launcher
From: Philip Sanderson <philip.k.sanderson at gmail.com>

Rusty Russell wrote:
> Ah, it will appear as /dev/hwrng.  It's a weirdness of Linux that our actual
> hardware number generators are not wired up to /dev/random...

Reflected this in the documentation, thanks :-)

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff --git a/Documentation/lguest/lguest.txt b/Documentation/lguest/lguest.txt
--- a/Documentation/lguest/lguest.txt
+++ b/Documentation/lguest/lguest.txt
@@ -114,6 +114,11 @@ Running Lguest:
   See http://linux-net.osdl.org/index.php/Bridge for general information
   on how to get bridging working.
 
+- Random number generation. Using the --rng option will provide a
+  /dev/hwrng in the guest that will read from the host's /dev/random.
+  Use this option in conjunction with rng-tools (see ../hw_random.txt)
+  to provide entropy to the guest kernel's /dev/random.
+
 There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest
 
 Good luck!