Re: [Patch] NULL pointer deref with corrupted squashfs image

[Eric Sesterhenn <snakebyte@gmx.de>]

* Tom Rini (trini@kernel.crashing.org) wrote:
> On Tue, Jan 20, 2009 at 05:47:14PM +0100, Eric Sesterhenn wrote:
> > * J=C3=B6rn Engel (joern@logfs.org) wrote:
> > > On Fri, 16 January 2009 16:07:00 -0700, Tom Rini wrote:
> > > >=20
> > > > Sounds like a plan to me, except maybe zlib_inflate_unsafe() and a
> > > > comment above the wrapper saying what/why is going on?
> > >=20
> > > Eric, will you do the honors?  Since you did all the hard work before,
> > > you derserve the fame as well. :)
> >=20
> > Since I am not sure either about xtensa I added chris to the cc list.
>=20
> How about we just change all callers from arch/*/boot to use the _unsafe
> version?  Then..
>=20
> > +/*
> > +    These two wrappers decide wheter strm->next_out gets checked for N=
ULL.
> > +    The zlib_inflate_unsafe() version got added because the PPC zImage
> > +    gets extracted to memory address 0 and therefore
> > +    we avoid this check for zlib_inflate_unsafe()
>=20
> These two wrappers decide wheter strm->next_out gets checked for NULL.
> The zlib_inflate_unsafe() version is primarily used in the pre-Linux
> 'boot' directory code to allow for extraction to memory address 0 and
> therefore we avoid this check.

This integrates Feedback from Tom to change xtensa and a comment, and
the callee/caller replace noticed by joern.




Some callers of zlib_inflate() might accidentally pass a NULL
pointer in strm->next_out which zlib_inflate() should catch.
Others like the powerpc gunzip_partial expect to be able
to extract a zImage to memory location 0. This introduces
zlib_inflate_usafe() for those and adds a check for the rest


Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>

--- linux/arch/powerpc/boot/gunzip_util.c.orig	2009-01-21 09:27:39.00000000=
0 +0100
+++ linux/arch/powerpc/boot/gunzip_util.c	2009-01-21 09:27:51.000000000 +01=
00
@@ -109,7 +109,7 @@ int gunzip_partial(struct gunzip_state *
=20
 		state->s.next_out =3D dst;
 		state->s.avail_out =3D dstlen;
-		r =3D zlib_inflate(&state->s, Z_FULL_FLUSH);
+		r =3D zlib_inflate_unsafe(&state->s, Z_FULL_FLUSH);
 		if (r !=3D Z_OK && r !=3D Z_STREAM_END)
 			fatal("inflate returned %d msg: %s\n\r", r, state->s.msg);
 		len =3D state->s.next_out - (unsigned char *)dst;
--- linux/arch/xtensa/boot/lib/zmem.c.orig	2009-01-21 09:22:44.000000000 +0=
100
+++ linux/arch/xtensa/boot/lib/zmem.c	2009-01-21 09:22:26.000000000 +0100
@@ -68,7 +68,7 @@ void gunzip (void *dst, int dstlen, unsi
         s.avail_in =3D *lenp - i;
         s.next_out =3D dst;
         s.avail_out =3D dstlen;
-        r =3D zlib_inflate(&s, Z_FINISH);
+        r =3D zlib_inflate_unsafe(&s, Z_FINISH);
         if (r !=3D Z_OK && r !=3D Z_STREAM_END) {
                 //puts("inflate returned "); puthex(r); puts("\n");
                 exit();
--- linux/include/linux/zlib.h.orig	2009-01-21 09:27:28.000000000 +0100
+++ linux/include/linux/zlib.h	2009-01-21 09:28:55.000000000 +0100
@@ -329,7 +329,23 @@ extern int zlib_inflateInit (z_streamp s
 */
=20
=20
-extern int zlib_inflate (z_streamp strm, int flush);
+extern int __zlib_inflate (z_streamp strm, int flush, int check_out);
+/*
+    These two wrappers decide wheter strm->next_out gets checked for NULL.
+    The zlib_inflate_unsafe() version is primarily used in the pre-Linux
+    'boot' directory code to allow for extraction to memory address 0 and
+    therefore we avoid this check.
+*/
+static inline int zlib_inflate(z_streamp strm, int flush)
+{
+	return __zlib_inflate(strm, flush, 1);
+}
+
+static inline int zlib_inflate_unsafe(z_streamp strm, int flush)
+{
+	return __zlib_inflate(strm, flush, 0);
+}
+
 /*
     inflate decompresses as much data as possible, and stops when the input
   buffer becomes empty or the output buffer becomes full. It may introduce
--- linux/lib/zlib_inflate/inflate.c.orig	2009-01-21 09:27:11.000000000 +01=
00
+++ linux/lib/zlib_inflate/inflate.c	2009-01-21 09:29:10.000000000 +0100
@@ -329,7 +329,7 @@ static int zlib_inflateSyncPacket(z_stre
    will return Z_BUF_ERROR if it has not reached the end of the stream.
  */
=20
-int zlib_inflate(z_streamp strm, int flush)
+int __zlib_inflate(z_streamp strm, int flush, int check_out)
 {
     struct inflate_state *state;
     const unsigned char *next;  /* next input */
@@ -347,8 +347,10 @@ int zlib_inflate(z_streamp strm, int flu
     static const unsigned short order[19] =3D /* permutation of code lengt=
hs */
         {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
=20
-    /* Do not check for strm->next_out =3D=3D NULL here as ppc zImage
-       inflates to strm->next_out =3D 0 */
+    /* We only check strm->next_out if the caller requests it,
+       since ppc extracts the ppc zImage to 0 */
+    if (check_out && !strm->next_out)
+        return Z_STREAM_ERROR;
=20
     if (strm =3D=3D NULL || strm->state =3D=3D NULL ||
         (strm->next_in =3D=3D NULL && strm->avail_in !=3D 0))
--- linux/lib/zlib_inflate/inflate_syms.c.orig	2009-01-21 09:27:16.00000000=
0 +0100
+++ linux/lib/zlib_inflate/inflate_syms.c	2009-01-21 09:27:51.000000000 +01=
00
@@ -11,7 +11,7 @@
 #include <linux/zlib.h>
=20
 EXPORT_SYMBOL(zlib_inflate_workspacesize);
-EXPORT_SYMBOL(zlib_inflate);
+EXPORT_SYMBOL(__zlib_inflate);
 EXPORT_SYMBOL(zlib_inflateInit2);
 EXPORT_SYMBOL(zlib_inflateEnd);
 EXPORT_SYMBOL(zlib_inflateReset);