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Another heap out of bounds read in bash


From: Hanno Böck
Subject: Another heap out of bounds read in bash
Date: Sat, 9 Jul 2016 00:25:31 +0200

Hi,

I discovered a heap out of bounds read, visible with address sanitizer
(also with valgrind).

To reproduce:
* Build bash with address sanitizer:
./configure CFLAGS="-fsanitize=address -g" CXX="-fsanitize=addres -g"
LDFLAGS="-fsanitize=address" --without-bash-malloc
* Run bash: ./bash
* Type & and [tab]

This will cause an out of bounds read in the function check_redir. Full
asan report is below.

The problem is this line:
  prev_char = rl_line_buffer[ti - 1];
if ti is 0 then this is an invalid memory read. I've attached a patch
to workaround the issue (not sure if you like the style, it's using
the ? operator to check for ti>0 and assigns a zero byte to prev_char
if it's 0.).


-----------------
==9564==ERROR: AddressSanitizer: heap-buffer-overflow on address
0x61100000887f at pc 0x510510 bp 0x7ffdff70c940 sp 0x7ffdff70c938
READ of size 1 at 0x61100000887f thread T0
    #0 0x51050f in check_redir /mnt/ram/bash-4.4-rc1/bashline.c:1284
    #1 0x5114e8 in
attempt_shell_completion /mnt/ram/bash-4.4-rc1/bashline.c:1478
    #2 0x5d2ea4 in
gen_completion_matches /mnt/ram/bash-4.4-rc1/lib/readline/complete.c:1231
    #3 0x5d7455 in
rl_complete_internal /mnt/ram/bash-4.4-rc1/lib/readline/complete.c:2045
    #4 0x5d0084 in
rl_complete /mnt/ram/bash-4.4-rc1/lib/readline/complete.c:439
    #5 0x5bdc82 in
_rl_dispatch_subseq /mnt/ram/bash-4.4-rc1/lib/readline/readline.c:859
    #6 0x5bd855 in
_rl_dispatch /mnt/ram/bash-4.4-rc1/lib/readline/readline.c:802
    #7 0x5bd051 in
readline_internal_char /mnt/ram/bash-4.4-rc1/lib/readline/readline.c:629
    #8 0x5bd0e1 in
readline_internal_charloop /mnt/ram/bash-4.4-rc1/lib/readline/readline.c:656
    #9 0x5bd10a in
readline_internal /mnt/ram/bash-4.4-rc1/lib/readline/readline.c:670
    #10 0x5bc71f in
readline /mnt/ram/bash-4.4-rc1/lib/readline/readline.c:376
    #11 0x42f07d in
yy_readline_get /usr/homes/chet/src/bash/src/parse.y:1454
    #12 0x42ef29 in yy_getc /usr/homes/chet/src/bash/src/parse.y:1388
    #13 0x43125b in shell_getc /usr/homes/chet/src/bash/src/parse.y:2290
    #14 0x433c64 in read_token /usr/homes/chet/src/bash/src/parse.y:3105
    #15 0x432790 in yylex /usr/homes/chet/src/bash/src/parse.y:2666
    #16 0x4276db in yyparse /mnt/ram/bash-4.4-rc1/y.tab.c:1832
    #17 0x426741 in parse_command /mnt/ram/bash-4.4-rc1/eval.c:258
    #18 0x426982 in read_command /mnt/ram/bash-4.4-rc1/eval.c:302
    #19 0x425e01 in reader_loop /mnt/ram/bash-4.4-rc1/eval.c:149
    #20 0x420f29 in main /mnt/ram/bash-4.4-rc1/shell.c:769
    #21 0x7f640864978f in __libc_start_main (/lib64/libc.so.6+0x2078f)
    #22 0x41fc68 in _start (/mnt/ram/bash-4.4-rc1/bash+0x41fc68)

0x61100000887f is located 1 bytes to the left of 256-byte region
[0x611000008880,0x611000008980)
allocated by thread T0 here:
    #0 0x7f6408e789af in malloc
(/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libasan.so.1+0x549af)
    #1 0x533846 in xmalloc /mnt/ram/bash-4.4-rc1/xmalloc.c:112
    #2 0x5beb35 in
readline_initialize_everything 
/mnt/ram/bash-4.4-rc1/lib/readline/readline.c:1194
    #3 0x5be9e6 in
rl_initialize /mnt/ram/bash-4.4-rc1/lib/readline/readline.c:1101
    #4 0x50bcbb in
initialize_readline /mnt/ram/bash-4.4-rc1/bashline.c:482
    #5 0x42efa6 in
yy_readline_get /usr/homes/chet/src/bash/src/parse.y:1440
    #6 0x42ef29 in yy_getc /usr/homes/chet/src/bash/src/parse.y:1388
    #7 0x43125b in shell_getc /usr/homes/chet/src/bash/src/parse.y:2290
    #8 0x433c64 in read_token /usr/homes/chet/src/bash/src/parse.y:3105
    #9 0x432790 in yylex /usr/homes/chet/src/bash/src/parse.y:2666
    #10 0x4276db in yyparse /mnt/ram/bash-4.4-rc1/y.tab.c:1832
    #11 0x426741 in parse_command /mnt/ram/bash-4.4-rc1/eval.c:258
    #12 0x426982 in read_command /mnt/ram/bash-4.4-rc1/eval.c:302
    #13 0x425e01 in reader_loop /mnt/ram/bash-4.4-rc1/eval.c:149
    #14 0x420f29 in main /mnt/ram/bash-4.4-rc1/shell.c:769
    #15 0x7f640864978f in __libc_start_main (/lib64/libc.so.6+0x2078f)

SUMMARY: AddressSanitizer:
heap-buffer-overflow /mnt/ram/bash-4.4-rc1/bashline.c:1284 check_redir
Shadow bytes around the buggy address:
  0x0c227fff90b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff90c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff90d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff90e0: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x0c227fff90f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c227fff9100: 00 00 fa fa fa fa fa fa fa fa fa fa fa fa fa[fa]
  0x0c227fff9110: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c227fff9120: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c227fff9130: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x0c227fff9140: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c227fff9150: 00 00 00 00 00 00 00 05 fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Contiguous container OOB:fc
  ASan internal:           fe
==9564==ABORTING



-- 
Hanno Böck
https://hboeck.de/

mail/jabber: address@hidden
GPG: BBB51E42

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