bzip2/SOURCES/0001-Accept-as-many-selectors-as-the-file-format-allows.patch

From 5c93a2ef05285f3e8946aab185c0b44b5abe999f Mon Sep 17 00:00:00 2001
From: Andrew Lukoshko <alukoshko@almalinux.org>
Date: Fri, 15 Nov 2024 13:54:11 +0000
Subject: [PATCH] Accept as many selectors as the file format allows

But ignore any larger than the theoretical maximum, BZ_MAX_SELECTORS.

The theoretical maximum number of selectors depends on the maximum
blocksize (900000 bytes) and the number of symbols (50) that can be
encoded with a different Huffman tree. BZ_MAX_SELECTORS is 18002.

But the bzip2 file format allows the number of selectors to be encoded
with 15 bits (because 18002 isn't a factor of 2 and doesn't fit in
14 bits). So the file format maximum is 32767 selectors.

Some bzip2 encoders might actually have written out more selectors
than the theoretical maximum because they rounded up the number of
selectors to some convenient factor of 8.

The extra 14766 selectors can never be validly used by the decompression
algorithm. So we can read them, but then discard them.

This is effectively what was done (by accident) before we added a
check for nSelectors to be at most BZ_MAX_SELECTORS to mitigate
CVE-2019-12900.

The extra selectors were written out after the array inside the
EState struct. But the struct has extra space allocated after the
selector arrays of 18060 bytes (which is larger than 14766).
All of which will be initialized later (so the overwrite of that
space with extra selector values would have been harmless).

Backport of upstream commit b07b105d1b66e32760095e3602261738443b9e13
---
 compress.c   |  2 +-
 decompress.c | 10 ++++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/compress.c b/compress.c
index caf7696..19b662b 100644
--- a/compress.c
+++ b/compress.c
@@ -454,7 +454,7 @@ void sendMTFValues ( EState* s )
 
    AssertH( nGroups < 8, 3002 );
    AssertH( nSelectors < 32768 &&
-            nSelectors <= (2 + (900000 / BZ_G_SIZE)),
+            nSelectors <= BZ_MAX_SELECTORS,
             3003 );
 
 
diff --git a/decompress.c b/decompress.c
index b6e0a29..78060c9 100644
--- a/decompress.c
+++ b/decompress.c
@@ -287,7 +287,7 @@ Int32 BZ2_decompress ( DState* s )
       GET_BITS(BZ_X_SELECTOR_1, nGroups, 3);
       if (nGroups < 2 || nGroups > 6) RETURN(BZ_DATA_ERROR);
       GET_BITS(BZ_X_SELECTOR_2, nSelectors, 15);
-      if (nSelectors < 1 || nSelectors > BZ_MAX_SELECTORS) RETURN(BZ_DATA_ERROR);
+      if (nSelectors < 1) RETURN(BZ_DATA_ERROR);
       for (i = 0; i < nSelectors; i++) {
          j = 0;
          while (True) {
@@ -296,8 +296,14 @@ Int32 BZ2_decompress ( DState* s )
             j++;
             if (j >= nGroups) RETURN(BZ_DATA_ERROR);
          }
-         s->selectorMtf[i] = j;
+         /* Having more than BZ_MAX_SELECTORS doesn't make much sense
+            since they will never be used, but some implementations might
+            "round up" the number of selectors, so just ignore those. */
+         if (i < BZ_MAX_SELECTORS)
+           s->selectorMtf[i] = j;
       }
+      if (nSelectors > BZ_MAX_SELECTORS)
+        nSelectors = BZ_MAX_SELECTORS;
 
       /*--- Undo the MTF values for the selectors. ---*/
       {
-- 
2.43.5