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Reduce an unnecessary O(N^3) loop in lexer.

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The lexer's handling of operators contained an O(N^3) hazard when
dealing with long strings of + or - characters; it seems hard to
prevent this case from being O(N^2), but the additional N multiplier
was not needed.

Backpatch all the way since this has been there since 7.x, and it
presents at least a mild hazard in that trying to do Bind, PREPARE or
EXPLAIN on a hostile query could take excessive time (without
honouring cancels or timeouts) even if the query was never executed.
This commit is contained in:
Andrew Gierth
2018-08-23 16:35:33 +01:00
parent 5ca0077419
commit d4a63f8297
3 changed files with 61 additions and 22 deletions
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27
src/backend/parser/scan.l
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@@ -885,20 +885,33 @@ other .
* to forbid operator names like '?-' that could not be
* sequences of SQL operators.
*/
while (nchars > 1 &&
(yytext[nchars - 1] == '+' ||
yytext[nchars - 1] == '-'))
if (nchars > 1 &&
(yytext[nchars - 1] == '+' ||
yytext[nchars - 1] == '-'))
{
int ic;
for (ic = nchars - 2; ic >= 0; ic--)
{
if (strchr("~!@#^&|`?%", yytext[ic]))
char c = yytext[ic];
if (c == '~' || c == '!' || c == '@' ||
c == '#' || c == '^' || c == '&' ||
c == '|' || c == '`' || c == '?' ||
c == '%')
break;
}
if (ic >= 0)
break; /* found a char that makes it OK */
nchars--; /* else remove the +/-, and check again */
if (ic < 0)
{
/*
* didn't find a qualifying character, so remove
* all trailing [+-]
*/
do {
nchars--;
} while (nchars > 1 &&
(yytext[nchars - 1] == '+' ||
yytext[nchars - 1] == '-'));
}
}
SET_YYLLOC();