ocfs2: validate external xattr entries when reading metadata

Summary

In the Linux kernel, the following vulnerability has been resolved: ocfs2: validate external xattr entries when reading metadata ocfs2_validate_xattr_block() checks the xattr block header before the block reaches higher-level xattr users, but it does not verify that a non-indexed block's xh_count and entry offsets fit inside the block. Indexed buckets likewise reach list/get consumers after ECC without an entry-bounds check. Use the flat xattr entry validator for non-indexed external xattr blocks, and use a bucket-specific validator for indexed buckets at metadata read time. The bucket validator keeps the entry array bounded by the first bucket block while checking name/value offsets against the bucket block they target. Reject corrupted external xattr metadata before listxattr() or getxattr() can walk out-of-range entry arrays or name/value offsets. Validation reproduced this kernel report: BUG: KASAN: use-after-free in ocfs2_xattr_list_entries+0xd7/0x190 Read of size 1 at addr ffff88810a654007 by task ocfs2_xattr_lis/630 Call Trace: dump_stack_lvl+0x66/0xa0 print_report+0xce/0x630 kasan_report+0xe0/0x110 ocfs2_xattr_list_entries+0xd7/0x190 ocfs2_listxattr+0x3f6/0x610 listxattr+0x90/0xe0 path_listxattrat+0xed/0x220 do_syscall_64+0x115/0x6a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f