busybox: backport fix for CVE-2021-28831

This backports a fix for the low priority CVE-2021-28831:
  decompress_gunzip.c in BusyBox through 1.32.1 mishandles the error bit
  on the huft_build result pointer, with a resultant invalid free or
  segmentation fault, via malformed gzip data.

Signed-off-by: Hauke Mehrtens <[email protected]>

package/utils/busybox/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=busybox
 PKG_VERSION:=1.33.0
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 PKG_FLAGS:=essential
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2

package/utils/busybox/patches/005-backport-CVE-2021-28831.patch

@@ -0,0 +1,52 @@
+From f25d254dfd4243698c31a4f3153d4ac72aa9e9bd Mon Sep 17 00:00:00 2001
+From: Samuel Sapalski <[email protected]>
+Date: Wed, 3 Mar 2021 16:31:22 +0100
+Subject: decompress_gunzip: Fix DoS if gzip is corrupt
+
+On certain corrupt gzip files, huft_build will set the error bit on
+the result pointer. If afterwards abort_unzip is called huft_free
+might run into a segmentation fault or an invalid pointer to
+free(p).
+
+In order to mitigate this, we check in huft_free if the error bit
+is set and clear it before the linked list is freed.
+
+Signed-off-by: Samuel Sapalski <[email protected]>
+Signed-off-by: Peter Kaestle <[email protected]>
+Signed-off-by: Denys Vlasenko <[email protected]>
+---
+ archival/libarchive/decompress_gunzip.c | 12 ++++++++++--
+ 1 file changed, 10 insertions(+), 2 deletions(-)
+
+--- a/archival/libarchive/decompress_gunzip.c
++++ b/archival/libarchive/decompress_gunzip.c
+@@ -220,10 +220,20 @@ static const uint8_t border[] ALIGN1 = {
+  * each table.
+  * t: table to free
+  */
++#define BAD_HUFT(p) ((uintptr_t)(p) & 1)
++#define ERR_RET     ((huft_t*)(uintptr_t)1)
+ static void huft_free(huft_t *p)
+ {
+ 	huft_t *q;
+
++	/*
++	 * If 'p' has the error bit set we have to clear it, otherwise we might run
++	 * into a segmentation fault or an invalid pointer to free(p)
++	 */
++	if (BAD_HUFT(p)) {
++		p = (huft_t*)((uintptr_t)(p) ^ (uintptr_t)(ERR_RET));
++	}
++
+ 	/* Go through linked list, freeing from the malloced (t[-1]) address. */
+ 	while (p) {
+ 		q = (--p)->v.t;
+@@ -289,8 +299,6 @@ static unsigned fill_bitbuffer(STATE_PAR
+  * or a valid pointer to a Huffman table, ORed with 0x1 if incompete table
+  * is given: "fixed inflate" decoder feeds us such data.
+  */
+-#define BAD_HUFT(p) ((uintptr_t)(p) & 1)
+-#define ERR_RET     ((huft_t*)(uintptr_t)1)
+ static huft_t* huft_build(const unsigned *b, const unsigned n,
+ 			const unsigned s, const struct cp_ext *cp_ext,
+ 			unsigned *m)