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

From: Eric Sesterhenn <[email-masked]>
Date: Tue, 20 Jan 2009 17:47:14 +0100

* Jörn Engel ([email-masked]) wrote:
> On Fri, 16 January 2009 16:07:00 -0700, Tom Rini wrote:
> > 
> > Sounds like a plan to me, except maybe zlib_inflate_unsafe() and a
> > comment above the wrapper saying what/why is going on?
> 
> Eric, will you do the honors?  Since you did all the hard work before,
> you derserve the fame as well. :)

Since I am not sure either about xtensa I added chris to the cc list.

Some callees 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 <[email-masked]>

--- linux/arch/powerpc/boot/gunzip_util.c.orig	2009-01-20 10:23:11.000000000 +0100
+++ linux/arch/powerpc/boot/gunzip_util.c	2009-01-20 10:23:31.000000000 +0100
@@ -109,7 +109,7 @@ int gunzip_partial(struct gunzip_state *
 
 		state->s.next_out = dst;
 		state->s.avail_out = dstlen;
-		r = zlib_inflate(&state->s, Z_FULL_FLUSH);
+		r = zlib_inflate_unsafe(&state->s, Z_FULL_FLUSH);
 		if (r != Z_OK && r != Z_STREAM_END)
 			fatal("inflate returned %d msg: %s\n\r", r, state->s.msg);
 		len = state->s.next_out - (unsigned char *)dst;
--- linux/include/linux/zlib.h.orig	2009-01-20 10:11:33.000000000 +0100
+++ linux/include/linux/zlib.h	2009-01-20 10:19:56.000000000 +0100
@@ -329,7 +329,23 @@ extern int zlib_inflateInit (z_streamp s
 */

-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 got added because the PPC zImage
+    gets extracted to memory address 0 and therefore
+    we avoid this check for zlib_inflate_unsafe()
+*/
+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_syms.c.orig	2009-01-20 10:22:21.000000000 +0100
+++ linux/lib/zlib_inflate/inflate_syms.c	2009-01-20 10:22:32.000000000 +0100
@@ -11,7 +11,7 @@
 #include <linux/zlib.h>
 
 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);
--- linux/lib/zlib_inflate/inflate.c.orig	2009-01-20 10:20:14.000000000 +0100
+++ linux/lib/zlib_inflate/inflate.c	2009-01-20 10:22:03.000000000 +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.
  */
 
-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] = /* permutation of code lengths */
         {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
 
-    /* Do not check for strm->next_out == NULL here as ppc zImage
-       inflates to strm->next_out = 0 */
+    /* We only check strm->next_out if the callee requests it,
+       since ppc extracts the ppc zImage to 0 */
+    if (check_out && !strm->next_out)
+        return Z_STREAM_ERROR;
 
     if (strm == NULL || strm->state == NULL ||
         (strm->next_in == NULL && strm->avail_in != 0))