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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
View File

@ -885,20 +885,33 @@ other .
* to forbid operator names like '?-' that could not be * to forbid operator names like '?-' that could not be
* sequences of SQL operators. * sequences of SQL operators.
*/ */
while (nchars > 1 && if (nchars > 1 &&
(yytext[nchars - 1] == '+' || (yytext[nchars - 1] == '+' ||
yytext[nchars - 1] == '-')) yytext[nchars - 1] == '-'))
{ {
int ic; int ic;
for (ic = nchars - 2; ic >= 0; 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; break;
} }
if (ic >= 0) if (ic < 0)
break; /* found a char that makes it OK */ {
nchars--; /* else remove the +/-, and check again */ /*
* didn't find a qualifying character, so remove
* all trailing [+-]
*/
do {
nchars--;
} while (nchars > 1 &&
(yytext[nchars - 1] == '+' ||
yytext[nchars - 1] == '-'));
}
} }
SET_YYLLOC(); SET_YYLLOC();

27
src/fe_utils/psqlscan.l
View File

@ -817,20 +817,33 @@ other .
* to forbid operator names like '?-' that could not be * to forbid operator names like '?-' that could not be
* sequences of SQL operators. * sequences of SQL operators.
*/ */
while (nchars > 1 && if (nchars > 1 &&
(yytext[nchars - 1] == '+' || (yytext[nchars - 1] == '+' ||
yytext[nchars - 1] == '-')) yytext[nchars - 1] == '-'))
{ {
int ic; int ic;
for (ic = nchars - 2; ic >= 0; 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; break;
} }
if (ic >= 0) if (ic < 0)
break; /* found a char that makes it OK */ {
nchars--; /* else remove the +/-, and check again */ /*
* didn't find a qualifying character, so remove
* all trailing [+-]
*/
do {
nchars--;
} while (nchars > 1 &&
(yytext[nchars - 1] == '+' ||
yytext[nchars - 1] == '-'));
}
} }
if (nchars < yyleng) if (nchars < yyleng)

29
src/interfaces/ecpg/preproc/pgc.l
View File

@ -690,20 +690,33 @@ cppline {space}*#([^i][A-Za-z]*|{if}|{ifdef}|{ifndef}|{import})((\/\*[^*/]*\*+
* to forbid operator names like '?-' that could not be * to forbid operator names like '?-' that could not be
* sequences of SQL operators. * sequences of SQL operators.
*/ */
while (nchars > 1 && if (nchars > 1 &&
(yytext[nchars-1] == '+' || (yytext[nchars - 1] == '+' ||
yytext[nchars-1] == '-')) yytext[nchars - 1] == '-'))
{ {
int ic; int ic;
for (ic = nchars-2; ic >= 0; 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; break;
} }
if (ic >= 0) if (ic < 0)
break; /* found a char that makes it OK */ {
nchars--; /* else remove the +/-, and check again */ /*
* didn't find a qualifying character, so remove
* all trailing [+-]
*/
do {
nchars--;
} while (nchars > 1 &&
(yytext[nchars - 1] == '+' ||
yytext[nchars - 1] == '-'));
}
} }
if (nchars < yyleng) if (nchars < yyleng)