btrfs: zlib: zero-initialize zlib workspace

KMSAN reports uses of uninitialized memory in zlib's longest_match()
called on memory originating from zlib_alloc_workspace().
This issue is known by zlib maintainers and is claimed to be harmless,
but to be on the safe side we'd better initialize the memory.

Link: https://zlib.net/zlib_faq.html#faq36
Reported-by: [email protected]
CC: [email protected] # 5.4+
Signed-off-by: Alexander Potapenko <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: ramosian-glider

fs/btrfs/zlib.c

@@ -63,7 +63,7 @@ struct list_head *zlib_alloc_workspace(unsigned int level)
 
 	workspacesize = max(zlib_deflate_workspacesize(MAX_WBITS, MAX_MEM_LEVEL),
 			zlib_inflate_workspacesize());
-	workspace->strm.workspace = kvmalloc(workspacesize, GFP_KERNEL);
+	workspace->strm.workspace = kvzalloc(workspacesize, GFP_KERNEL);
 	workspace->level = level;
 	workspace->buf = NULL;
 	/*