hfsplus: fix uninit-value in copy_name

[ Upstream commit 0570730c

 ]

[syzbot reported]
BUG: KMSAN: uninit-value in sized_strscpy+0xc4/0x160
 sized_strscpy+0xc4/0x160
 copy_name+0x2af/0x320 fs/hfsplus/xattr.c:411
 hfsplus_listxattr+0x11e9/0x1a50 fs/hfsplus/xattr.c:750
 vfs_listxattr fs/xattr.c:493 [inline]
 listxattr+0x1f3/0x6b0 fs/xattr.c:840
 path_listxattr fs/xattr.c:864 [inline]
 __do_sys_listxattr fs/xattr.c:876 [inline]
 __se_sys_listxattr fs/xattr.c:873 [inline]
 __x64_sys_listxattr+0x16b/0x2f0 fs/xattr.c:873
 x64_sys_call+0x2ba0/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:195
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:3877 [inline]
 slab_alloc_node mm/slub.c:3918 [inline]
 kmalloc_trace+0x57b/0xbe0 mm/slub.c:4065
 kmalloc include/linux/slab.h:628 [inline]
 hfsplus_listxattr+0x4cc/0x1a50 fs/hfsplus/xattr.c:699
 vfs_listxattr fs/xattr.c:493 [inline]
 listxattr+0x1f3/0x6b0 fs/xattr.c:840
 path_listxattr fs/xattr.c:864 [inline]
 __do_sys_listxattr fs/xattr.c:876 [inline]
 __se_sys_listxattr fs/xattr.c:873 [inline]
 __x64_sys_listxattr+0x16b/0x2f0 fs/xattr.c:873
 x64_sys_call+0x2ba0/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:195
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
[Fix]
When allocating memory to strbuf, initialize memory to 0.

Reported-and-tested-by:  <syzbot+efde959319469ff8d4d7@syzkaller.appspotmail.com>
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Link: https://lore.kernel.org/r/tencent_8BBB6433BC9E1C1B7B4BDF1BF52574BA8808@qq.com
Reported-and-tested-by:  <syzbot+01ade747b16e9c8030e0@syzkaller.appspotmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>