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Prevent lexer from reading beyond the end of the buffer

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On Linux, valgrind complains about the overflow like this:

  Pass 1...
  ==20054== Invalid read of size 1
  ==20054==    at 0x406CDA: yylex (lexer.c:396)
  ==20054==    by 0x40207C: yyparse (asmy.c:2921)
  ==20054==    by 0x4086AF: main (main.c:351)
  ==20054==  Address 0x503a102 is 0 bytes after a block of size 23,538 alloc'd
  ==20054==    at 0x402994D: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
  ==20054==    by 0x406411: yy_create_buffer (lexer.c:147)
  ==20054==    by 0x404FE3: fstk_RunInclude (fstack.c:243)
  ==20054==    by 0x4025F5: yyparse (asmy.y:744)
  ==20054==    by 0x4086AF: main (main.c:351)
  ==20054==

This is a bit of a crude fix which simply exits the hashing loop when
we reach the end of the string. We should probably do some kind of
length calculation on the buffer instead.

Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
This commit is contained in:
Vegard Nossum
2012-10-21 05:51:48 +02:00
parent 8c2fb79c39
commit 2dfd937d7f
1 changed files with 9 additions and 0 deletions
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9
src/asm/lexer.c
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@@ -392,6 +392,15 @@ scanagain:
hash = 0;
s = pLexBuffer;
while (yyleng < nLexMaxLeng) {
/* XXX: Kludge warning! The dereference of s below
* may go beyond the end of the buffer. We use the
* following test to stop that from happening,
* without really understanding what the rest of
* the code is doing. This may not be the correct
* fix! */
if (!*s)
break;
yyleng += 1;
hash = ((hash << 1) + (toupper(*s))) % LEXHASHSIZE;
s += 1;