[PATCH] zstd: Require at least 8 byte buffer in entropy_common

[Julian Andres Klode]

This fixes the build on s390x which was rightfully complaining that
iend - 7 = buffer + 4 - 7 = buffer -3 is outside the array bounds.

../../grub-core/lib/zstd/entropy_common.c: In function ‘FSE_readNCount’:
../../grub-core/lib/zstd/entropy_common.c:121:28: error: array subscript -3 is 
outside array bounds of ‘char[4]’ [-Werror=array-bounds]
  121 |             if ((ip <= iend-7) || (ip + (bitCount>>3) <= iend-4)) {
      |                        ~~~~^~
../../grub-core/lib/zstd/entropy_common.c:77:14: note: while referencing 
‘buffer’
   77 |         char buffer[4];
      |              ^~~~~~
../../grub-core/lib/zstd/entropy_common.c:105:30: error: array subscript -1 is 
outside array bounds of ‘char[4]’ [-Werror=array-bounds]
  105 |                 if (ip < iend-5) {
      |                          ~~~~^~
../../grub-core/lib/zstd/entropy_common.c:77:14: note: while referencing 
‘buffer’
   77 |         char buffer[4];
      |              ^~~~~~
../../grub-core/lib/zstd/entropy_common.c:150:28: error: array subscript -3 is 
outside array bounds of ‘char[4]’ [-Werror=array-bounds]
  150 |             if ((ip <= iend-7) || (ip + (bitCount>>3) <= iend-4)) {
      |                        ~~~~^~
../../grub-core/lib/zstd/entropy_common.c:77:14: note: while referencing 
‘buffer’
   77 |         char buffer[4];
      |              ^~~~~~

This is fixed in more recent zstd versions in basically the same way,
but the new versions needs more work to import.

Signed-off-by: Julian Andres Klode <julian.klode@canonical.com>
---
 grub-core/lib/zstd/entropy_common.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/grub-core/lib/zstd/entropy_common.c 
b/grub-core/lib/zstd/entropy_common.c
index b12944e1d..834fa4b7d 100644
--- a/grub-core/lib/zstd/entropy_common.c
+++ b/grub-core/lib/zstd/entropy_common.c
@@ -72,9 +72,9 @@ size_t FSE_readNCount (short* normalizedCounter, unsigned* 
maxSVPtr, unsigned* t
     unsigned charnum = 0;
     int previous0 = 0;
 
-    if (hbSize < 4) {
+    if (hbSize < 8) {
         /* This function only works when hbSize >= 4 */
-        char buffer[4];
+        char buffer[8];
         memset(buffer, 0, sizeof(buffer));
         memcpy(buffer, headerBuffer, hbSize);
         {   size_t const countSize = FSE_readNCount(normalizedCounter, 
maxSVPtr, tableLogPtr,
@@ -83,7 +83,7 @@ size_t FSE_readNCount (short* normalizedCounter, unsigned* 
maxSVPtr, unsigned* t
             if (countSize > hbSize) return ERROR(corruption_detected);
             return countSize;
     }   }
-    assert(hbSize >= 4);
+    assert(hbSize >= 8);
 
     /* init */
     memset(normalizedCounter, 0, (*maxSVPtr+1) * 
sizeof(normalizedCounter[0]));   /* all symbols not present in NCount have a 
frequency of 0 */
-- 
2.33.1