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: syzbot+14d9e7602ebdf7ec0a60@syzkaller.appspotmail.com
CC: stable@vger.kernel.org # 5.4+
Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
index 01a13de..da7bb91 100644 (file)
--- a/fs/btrfs/zlib.c
+++ b/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;
        /*