btrfs-progs: check: Avoid reading beyond item boundary for inode_ref

btrfs-progs: check: Avoid reading beyond item boundary for inode_ref

When reading out name from inode_ref, it's possible that corrupted
name_len can lead to read beyond boundary of item or even extent buffer.

This happens when checking fuzzed image /tmp/bko-161811.raw, for both
lowmem mode and original mode.

ERROR: root 5 INODE REF[256 256] doesn't have related DIR_INDEX[256 504403158265495680] namelen 0 filename  filetype 0
ERROR: root 5 INODE REF[256 256] doesn't have related DIR_ITEM[256 4294967294] namelen 0 filename  filetype 0
WARNING: root 5 INODE_REF[256 256] name too long
==13022== Invalid read of size 8
==13022==    at 0x4C319BE: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==13022==    by 0x431518: read_extent_buffer (extent_io.c:863)
==13022==    by 0x474730: check_inode_ref (cmds-check.c:4307)
==13022==    by 0x475D65: check_inode_item (cmds-check.c:4890)
==13022==    by 0x476200: check_fs_first_inode (cmds-check.c:5011)
==13022==    by 0x476276: check_fs_root_v2 (cmds-check.c:5044)
==13022==    by 0x4769FB: check_fs_roots_v2 (cmds-check.c:5242)
==13022==    by 0x488B5B: cmd_check (cmds-check.c:13033)
==13022==    by 0x40A8C5: main (btrfs.c:246)
==13022==  Address 0x5c96780 is 0 bytes after a block of size 4,224 alloc'd
==13022==    at 0x4C2CF35: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==13022==    by 0x4307E0: __alloc_extent_buffer (extent_io.c:538)
==13022==    by 0x430C37: alloc_extent_buffer (extent_io.c:642)
==13022==    by 0x413DFE: btrfs_find_create_tree_block (disk-io.c:193)
==13022==    by 0x414370: read_tree_block_fs_info (disk-io.c:340)
==13022==    by 0x40B5D5: read_tree_block (disk-io.h:125)
==13022==    by 0x40CFD2: read_node_slot (ctree.c:652)
==13022==    by 0x40E5EB: btrfs_search_slot (ctree.c:1172)
==13022==    by 0x4761A8: check_fs_first_inode (cmds-check.c:5001)
==13022==    by 0x476276: check_fs_root_v2 (cmds-check.c:5044)
==13022==    by 0x4769FB: check_fs_roots_v2 (cmds-check.c:5242)
==13022==    by 0x488B5B: cmd_check (cmds-check.c:13033)
=

Fix it by double checking inode_ref, name_len against item boundary
before trying to read out name from extent buffer, for both original
mode and lowmem mode.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>