bash -n: stack overflow in extract_delimited_string()

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From	Jakub Wilk <jwilk@jwilk.net>
Newsgroups	gnu.bash.bug
Subject	bash -n: stack overflow in extract_delimited_string()
Date	Mon, 3 Aug 2020 11:30:55 +0200
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Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2 -Wno-parentheses -Wno-format-security
uname output: Linux debian 4.19.0-9-cloud-amd64 #1 SMP Debian 4.19.118-2+deb10u1 (2020-06-07) x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.0
Patch Level: 18
Release Status: release

bash crashes with stack overflow when checking syntax of this crafted script:

   $ ulimit -s
   8192

   $ printf 'x[$(($(fi)))`\n%050000d\n][`]\n' | tr 0 '(' | bash -n
   bash: command substitution: line 4: syntax error near unexpected token `fi'
   bash: command substitution: line 4: `fi)))`'
   Segmentation fault

Backtrace:

   #0  0x000056084f0c841c in extract_delimited_string (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., sindex=sindex@entry=0x7ffde769a0fc, opener=opener@entry=0x56084f14bc31 "(", alt_opener=alt_opener@entry=0x56084f14bc31 "(", closer=closer@entry=0x56084f14a41f ")", flags=flags@entry=9) at subst.c:1326
   #1  0x000056084f0c8819 in extract_delimited_string (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., sindex=sindex@entry=0x7ffde769a1ac, opener=opener@entry=0x56084f14bc31 "(", alt_opener=alt_opener@entry=0x56084f14bc31 "(", closer=closer@entry=0x56084f14a41f ")", flags=flags@entry=9) at subst.c:1400
   #2  0x000056084f0c8819 in extract_delimited_string (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., sindex=sindex@entry=0x7ffde769a25c, opener=opener@entry=0x56084f14bc31 "(", alt_opener=alt_opener@entry=0x56084f14bc31 "(", closer=closer@entry=0x56084f14a41f ")", flags=flags@entry=9) at subst.c:1400
   ...
   #47577 0x000056084f0c8819 in extract_delimited_string (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., sindex=sindex@entry=0x7ffde7e9662c, opener=opener@entry=0x56084f14bc31 "(", alt_opener=alt_opener@entry=0x56084f14bc31 "(", closer=closer@entry=0x56084f14a41f ")", flags=flags@entry=9) at subst.c:1400
   #47578 0x000056084f0c8819 in extract_delimited_string (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., sindex=sindex@entry=0x7ffde7e966dc, opener=opener@entry=0x56084f14bc31 "(", alt_opener=alt_opener@entry=0x56084f14bc31 "(", closer=closer@entry=0x56084f14a41f ")", flags=flags@entry=9) at subst.c:1400
   #47579 0x000056084f0c8c02 in extract_delimited_string (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., sindex=sindex@entry=0x7ffde7e9676c, opener=opener@entry=0x56084f14bc30 "$(", alt_opener=alt_opener@entry=0x56084f14bc31 "(", closer=closer@entry=0x56084f14a41f ")", flags=flags@entry=9) at subst.c:1410
   #47580 0x000056084f0c917b in skip_matched_pair (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., start=<optimized out>, flags=flags@entry=0, close=93, open=91) at subst.c:1799
   #47581 0x000056084f0ca485 in skipsubscript (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., start=<optimized out>, flags=flags@entry=0) at subst.c:1827
   #47582 0x000056084f0a62be in assignment (string=string@entry=0x56084f2a6008 "x[$(($(fi)))`\n", '(' <repeats 186 times>..., flags=0) at general.c:440
   #47583 0x000056084f0a034c in read_token_word (character=10) at /usr/homes/chet/src/bash/src/parse.y:5305
   #47584 read_token (command=<optimized out>) at /usr/homes/chet/src/bash/src/parse.y:3445
   #47585 read_token (command=0) at /usr/homes/chet/src/bash/src/parse.y:3202
   #47586 0x000056084f0a2698 in yylex () at /usr/homes/chet/src/bash/src/parse.y:2761
   #47587 yyparse () at y.tab.c:1842
   #47588 0x000056084f098486 in parse_command () at eval.c:303
   #47589 0x000056084f0985a4 in read_command () at eval.c:347
   #47590 0x000056084f0987b8 in reader_loop () at eval.c:143
   #47591 0x000056084f09715d in main (argc=2, argv=0x7ffde7e979a8, env=0x7ffde7e979c0) at shell.c:805

-- 
Jakub Wilk

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bash -n: stack overflow in extract_delimited_string() Jakub Wilk <jwilk@jwilk.net> - 2020-08-03 11:30 +0200

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