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Subject[PATCH] zlib double-free bug
Recently CERT published an advisory, warning about a bug in zlib where
a chunk of memory could get freed twice, depending on the data being
decompressed, which could potentially give a way to attack a system
using zlib. The reference is

http://www.cert.org/advisories/CA-2002-07.html

All 3 of the versions of zlib in the current 2.4 kernel have this bug.
The version in 2.5 doesn't because it handles memory allocation in a
different way.

The patch below fixes this bug in each of the three copies of zlib.c,
in the same way that it is fixed in the zlib-1.1.4 release (basically
by making sure that s->sub.trees.blens is always freed whenever, and
only when, s->mode is changed from BTREE or DTREE to some other value).

In the longer term I recommend that the 2.5.x changes to use a single
copy of zlib in lib/zlib_{deflate,inflate} should be back-ported to
2.4. For now, this patch should be applied to 2.4.x since the bug is
a potential security hole if you are using PPP with Deflate
compression.

The patch also raises the minimum value of `windowBits' for
compression from 8 to 9, since using windowBits==8 causes memory
corruption (this was discovered by James Carlson, see
http://playground.sun.com/~carlsonj/ for details). Current versions
of pppd avoid using windowBits==8 for this reason, but it is better to
have zlib protect itself as well.

Paul.

diff -urN linux-2.4.19-pre3/arch/ppc/boot/lib/zlib.c pmac/arch/ppc/boot/lib/zlib.c
--- linux-2.4.19-pre3/arch/ppc/boot/lib/zlib.c Mon Mar 18 13:34:47 2002
+++ pmac/arch/ppc/boot/lib/zlib.c Mon Mar 18 21:15:55 2002
@@ -928,7 +928,10 @@
{
r = t;
if (r == Z_DATA_ERROR)
+ {
+ ZFREE(z, s->sub.trees.blens, s->sub.trees.nblens * sizeof(uInt));
s->mode = BADB;
+ }
LEAVE
}
s->sub.trees.index = 0;
@@ -964,6 +967,7 @@
if (i + j > 258 + (t & 0x1f) + ((t >> 5) & 0x1f) ||
(c == 16 && i < 1))
{
+ ZFREE(z, s->sub.trees.blens, s->sub.trees.nblens * sizeof(uInt));
s->mode = BADB;
z->msg = "invalid bit length repeat";
r = Z_DATA_ERROR;
@@ -991,7 +995,10 @@
if (t != Z_OK)
{
if (t == (uInt)Z_DATA_ERROR)
+ {
+ ZFREE(z, s->sub.trees.blens, s->sub.trees.nblens * sizeof(uInt));
s->mode = BADB;
+ }
r = t;
LEAVE
}
@@ -1003,11 +1010,11 @@
r = Z_MEM_ERROR;
LEAVE
}
- ZFREE(z, s->sub.trees.blens, s->sub.trees.nblens * sizeof(uInt));
s->sub.decode.codes = c;
s->sub.decode.tl = tl;
s->sub.decode.td = td;
}
+ ZFREE(z, s->sub.trees.blens, s->sub.trees.nblens * sizeof(uInt));
s->mode = CODES;
case CODES:
UPDATE
diff -urN linux-2.4.19-pre3/drivers/net/zlib.c pmac/drivers/net/zlib.c
--- linux-2.4.19-pre3/drivers/net/zlib.c Sat Apr 28 23:02:45 2001
+++ pmac/drivers/net/zlib.c Mon Mar 18 12:12:17 2002
@@ -14,7 +14,7 @@
*/

/*
- * ==FILEVERSION 971210==
+ * ==FILEVERSION 20020318==
*
* This marker is used by the Linux installation script to determine
* whether an up-to-date version of this file is already installed.
@@ -772,7 +772,7 @@
windowBits = -windowBits;
}
if (memLevel < 1 || memLevel > MAX_MEM_LEVEL || method != Z_DEFLATED ||
- windowBits < 8 || windowBits > 15 || level < 0 || level > 9 ||
+ windowBits < 9 || windowBits > 15 || level < 0 || level > 9 ||
strategy < 0 || strategy > Z_HUFFMAN_ONLY) {
return Z_STREAM_ERROR;
}
@@ -3860,10 +3860,12 @@
&s->sub.trees.tb, z);
if (t != Z_OK)
{
- ZFREE(z, s->sub.trees.blens);
r = t;
if (r == Z_DATA_ERROR)
+ {
+ ZFREE(z, s->sub.trees.blens);
s->mode = BADB;
+ }
LEAVE
}
s->sub.trees.index = 0;
@@ -3928,11 +3930,13 @@
#endif
t = inflate_trees_dynamic(257 + (t & 0x1f), 1 + ((t >> 5) & 0x1f),
s->sub.trees.blens, &bl, &bd, &tl, &td, z);
- ZFREE(z, s->sub.trees.blens);
if (t != Z_OK)
{
if (t == (uInt)Z_DATA_ERROR)
+ {
+ ZFREE(z, s->sub.trees.blens);
s->mode = BADB;
+ }
r = t;
LEAVE
}
@@ -3949,6 +3953,7 @@
s->sub.decode.tl = tl;
s->sub.decode.td = td;
}
+ ZFREE(z, s->sub.trees.blens);
s->mode = CODES;
case CODES:
UPDATE
diff -urN linux-2.4.19-pre3/fs/jffs2/zlib.c pmac/fs/jffs2/zlib.c
--- linux-2.4.19-pre3/fs/jffs2/zlib.c Mon Sep 24 09:31:33 2001
+++ pmac/fs/jffs2/zlib.c Mon Mar 18 21:16:32 2002
@@ -14,7 +14,7 @@
*/

/*
- * ==FILEVERSION 971210==
+ * ==FILEVERSION 20020318==
*
* This marker is used by the Linux installation script to determine
* whether an up-to-date version of this file is already installed.
@@ -772,7 +772,7 @@
windowBits = -windowBits;
}
if (memLevel < 1 || memLevel > MAX_MEM_LEVEL || method != Z_DEFLATED ||
- windowBits < 8 || windowBits > 15 || level < 0 || level > 9 ||
+ windowBits < 9 || windowBits > 15 || level < 0 || level > 9 ||
strategy < 0 || strategy > Z_HUFFMAN_ONLY) {
return Z_STREAM_ERROR;
}
@@ -3860,10 +3860,12 @@
&s->sub.trees.tb, z);
if (t != Z_OK)
{
- ZFREE(z, s->sub.trees.blens);
r = t;
if (r == Z_DATA_ERROR)
+ {
+ ZFREE(z, s->sub.trees.blens);
s->mode = BADB;
+ }
LEAVE
}
s->sub.trees.index = 0;
@@ -3928,11 +3930,13 @@
#endif
t = inflate_trees_dynamic(257 + (t & 0x1f), 1 + ((t >> 5) & 0x1f),
s->sub.trees.blens, &bl, &bd, &tl, &td, z);
- ZFREE(z, s->sub.trees.blens);
if (t != Z_OK)
{
if (t == (uInt)Z_DATA_ERROR)
+ {
+ ZFREE(z, s->sub.trees.blens);
s->mode = BADB;
+ }
r = t;
LEAVE
}
@@ -3949,6 +3953,7 @@
s->sub.decode.tl = tl;
s->sub.decode.td = td;
}
+ ZFREE(z, s->sub.trees.blens);
s->mode = CODES;
case CODES:
UPDATE
-
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