f2fs: explicitly null-terminate the xattr list

mainline inclusion
from mainline-v6.8-rc1
commit e26b6d39270f5eab0087453d9b544189a38c8564
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I92HXK
CVE: CVE-2023-52436

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e26b6d39270f5eab0087453d9b544189a38c8564



--------------------------------

When setting an xattr, explicitly null-terminate the xattr list.  This
eliminates the fragile assumption that the unused xattr space is always
zeroed.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Zizhi Wo <wozizhi@huawei.com>