[PATCH AUTOSEL 6.6 08/17] zstd: Fix array-index-out-of-bounds UBSAN warning

[Sasha Levin]

From: Nick Terrell <terrelln@xxxxxx>

[ Upstream commit 77618db346455129424fadbbaec596a09feaf3bb ]

Zstd used an array of length 1 to mean a flexible array for C89
compatibility. Switch to a C99 flexible array to fix the UBSAN warning.

Tested locally by booting the kernel and writing to and reading from a
BtrFS filesystem with zstd compression enabled. I was unable to reproduce
the issue before the fix, however it is a trivial change.

Link: https://lkml.kernel.org/r/20231012213428.1390905-1-nickrterrell@xxxxxxxxx
Reported-by: syzbot+1f2eb3e8cd123ffce499@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Reported-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Nick Terrell <terrelln@xxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 lib/zstd/common/fse_decompress.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/zstd/common/fse_decompress.c b/lib/zstd/common/fse_decompress.c
index a0d06095be83d..8dcb8ca39767c 100644
--- a/lib/zstd/common/fse_decompress.c
+++ b/lib/zstd/common/fse_decompress.c
@@ -312,7 +312,7 @@ size_t FSE_decompress_wksp(void* dst, size_t dstCapacity, const void* cSrc, size
 
 typedef struct {
     short ncount[FSE_MAX_SYMBOL_VALUE + 1];
-    FSE_DTable dtable[1]; /* Dynamically sized */
+    FSE_DTable dtable[]; /* Dynamically sized */
 } FSE_DecompressWksp;
 
 
-- 
2.42.0