This adds a length check to guarantee the retrieved index root is legit.

[  162.459513] BUG: KASAN: use-after-free in hdr_find_e.isra.0+0x10c/0x320
[  162.460176] Read of size 2 at addr ffff8880037bca99 by task mount/243
[  162.460851]
[  162.461252] CPU: 0 PID: 243 Comm: mount Not tainted 6.0.0-rc7 #42
[  162.461744] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[  162.462609] Call Trace:
[  162.462954]  <TASK>
[  162.463276]  dump_stack_lvl+0x49/0x63
[  162.463822]  print_report.cold+0xf5/0x689
[  162.464608]  ? unwind_get_return_address+0x3a/0x60
[  162.465766]  ? hdr_find_e.isra.0+0x10c/0x320
[  162.466975]  kasan_report+0xa7/0x130
[  162.467506]  ? _raw_spin_lock_irq+0xc0/0xf0
[  162.467998]  ? hdr_find_e.isra.0+0x10c/0x320
[  162.468536]  __asan_load2+0x68/0x90
[  162.468923]  hdr_find_e.isra.0+0x10c/0x320
[  162.469282]  ? cmp_uints+0xe0/0xe0
[  162.469557]  ? cmp_sdh+0x90/0x90
[  162.469864]  ? ni_find_attr+0x214/0x300
[  162.470217]  ? ni_load_mi+0x80/0x80
[  162.470479]  ? entry_SYSCALL_64_after_hwframe+0x63/0xcd
[  162.470931]  ? ntfs_bread_run+0x190/0x190
[  162.471307]  ? indx_get_root+0xe4/0x190
[  162.471556]  ? indx_get_root+0x140/0x190
[  162.471833]  ? indx_init+0x1e0/0x1e0
[  162.472069]  ? fnd_clear+0x115/0x140
[  162.472363]  ? _raw_spin_lock_irqsave+0x100/0x100
[  162.472731]  indx_find+0x184/0x470
[  162.473461]  ? sysvec_apic_timer_interrupt+0x57/0xc0
[  162.474429]  ? indx_find_buffer+0x2d0/0x2d0
[  162.474704]  ? do_syscall_64+0x3b/0x90
[  162.474962]  dir_search_u+0x196/0x2f0
[  162.475381]  ? ntfs_nls_to_utf16+0x450/0x450
[  162.475661]  ? ntfs_security_init+0x3d6/0x440
[  162.475906]  ? is_sd_valid+0x180/0x180
[  162.476191]  ntfs_extend_init+0x13f/0x2c0
[  162.476496]  ? ntfs_fix_post_read+0x130/0x130
[  162.476861]  ? iput.part.0+0x286/0x320
[  162.477325]  ntfs_fill_super+0x11e0/0x1b50
[  162.477709]  ? put_ntfs+0x1d0/0x1d0
[  162.477970]  ? vsprintf+0x20/0x20
[  162.478258]  ? set_blocksize+0x95/0x150
[  162.478538]  get_tree_bdev+0x232/0x370
[  162.478789]  ? put_ntfs+0x1d0/0x1d0
[  162.479038]  ntfs_fs_get_tree+0x15/0x20
[  162.479374]  vfs_get_tree+0x4c/0x130
[  162.479729]  path_mount+0x654/0xfe0
[  162.480124]  ? putname+0x80/0xa0
[  162.480484]  ? finish_automount+0x2e0/0x2e0
[  162.480894]  ? putname+0x80/0xa0
[  162.481467]  ? kmem_cache_free+0x1c4/0x440
[  162.482280]  ? putname+0x80/0xa0
[  162.482714]  do_mount+0xd6/0xf0
[  162.483264]  ? path_mount+0xfe0/0xfe0
[  162.484782]  ? __kasan_check_write+0x14/0x20
[  162.485593]  __x64_sys_mount+0xca/0x110
[  162.486024]  do_syscall_64+0x3b/0x90
[  162.486543]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
[  162.487141] RIP: 0033:0x7f9d374e948a
[  162.488324] Code: 48 8b 0d 11 fa 2a 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 008
[  162.489728] RSP: 002b:00007ffe30e73d18 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
[  162.490971] RAX: ffffffffffffffda RBX: 0000561cdb43a060 RCX: 00007f9d374e948a
[  162.491669] RDX: 0000561cdb43a260 RSI: 0000561cdb43a2e0 RDI: 0000561cdb442af0
[  162.492050] RBP: 0000000000000000 R08: 0000561cdb43a280 R09: 0000000000000020
[  162.492459] R10: 00000000c0ed0000 R11: 0000000000000206 R12: 0000561cdb442af0
[  162.493183] R13: 0000561cdb43a260 R14: 0000000000000000 R15: 00000000ffffffff
[  162.493644]  </TASK>
[  162.493908]
[  162.494214] The buggy address belongs to the physical page:
[  162.494761] page:000000003e38a3d5 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x37bc
[  162.496064] flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff)
[  162.497278] raw: 000fffffc0000000 ffffea00000df1c8 ffffea00000df008 0000000000000000
[  162.498928] raw: 0000000000000000 0000000000240000 00000000ffffffff 0000000000000000
[  162.500542] page dumped because: kasan: bad access detected
[  162.501057]
[  162.501242] Memory state around the buggy address:
[  162.502230]  ffff8880037bc980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[  162.502977]  ffff8880037bca00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[  162.503522] >ffff8880037bca80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[  162.503963]                             ^
[  162.504370]  ffff8880037bcb00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[  162.504766]  ffff8880037bcb80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
Signed-off-by: Edward Lo <edward.lo@ambergroup.io>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>