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Re: Out-of-bounds read in parse_comsub()


From: Eduardo A . Bustamante López
Subject: Re: Out-of-bounds read in parse_comsub()
Date: Fri, 27 Oct 2017 10:32:45 -0500
User-agent: NeoMutt/20170609 (1.8.3)

On Thu, Oct 26, 2017 at 11:07:57PM +0200, Jakub Wilk wrote:
[...]
> Bash Version: 20171020 snapshot
> 
> Apparently an out-of-bounds read can happen in parse_comsub() when checking
> script sytnax. To reproduce, rebuild bash with AddressSanitizer enabled and
> run:
> 
>   $ printf 
> '$(00\177%012d\1%d00\177%090d\177%028d(%0267d\177%010d<<-\276%019d\n\n' | 
> bash -n

I can reproduce this error too. It seems `ret' is missing a NUL terminator, so
`STREQN' reads past the allocated buffer.


I'm not sure if this is the right fix, but at least it makes the issue go away 
for me:


address@hidden:~/src/gnu/build-bash-devel$ CFLAGS='-g -O0 -fsanitize=address' 
../bash/configure --without-bash-malloc && make -j8
[...]
address@hidden:~/src/gnu/build-bash-devel$ printf 
'$(00\177%012d\1%d00\177%090d\177%028d(%0267d\177%010d<<-\276%019d\n\n' | 
./bash -n
./bash: line 1: unexpected EOF while looking for matching `)'
./bash: line 3: syntax error: unexpected end of file


diff --git a/parse.y b/parse.y
index 623648c6..67d9b3c3 100644
--- a/parse.y
+++ b/parse.y
@@ -3838,6 +3838,7 @@ eof_error:
              tind = lex_firstind;
              while ((tflags & LEX_STRIPDOC) && ret[tind] == '\t')
                tind++;
+             ret[retsize - 1] = '\0';
              if (STREQN (ret + tind, heredelim, hdlen))
                {
                  tflags &= ~(LEX_STRIPDOC|LEX_INHEREDOC|LEX_QUOTEDDOC);



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