Thread: [sqlsmith] Infinite recursion in bitshift
Hi,
sqlsmith just found another crasher:
select bit '1' >> (-2^31)::int;
This is due to an integer overflow in bitshiftright()/bitshiftleft()
leading to them recursively calling each other. Patch attached.
regards,
Andreas
>From cfdc425f75da268e1c2af08f936c59f34b69e577 Mon Sep 17 00:00:00 2001
From: Andreas Seltenreich <seltenreich@gmx.de>
Date: Fri, 14 Oct 2016 20:52:52 +0200
Subject: [PATCH] Fix possible infinite recursion on bitshift.
bitshiftright() and bitshiftleft() would recursively call each other
infinitely when the user passed a MIN_INT for the shift amount due to
an integer overflow. This patch reduces a negative shift amount to
-VARBITMAXLEN to avoid overflow.
---
src/backend/utils/adt/varbit.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/src/backend/utils/adt/varbit.c b/src/backend/utils/adt/varbit.c
index 75e6a46..d8ecfb6 100644
--- a/src/backend/utils/adt/varbit.c
+++ b/src/backend/utils/adt/varbit.c
@@ -1387,9 +1387,15 @@ bitshiftleft(PG_FUNCTION_ARGS)
/* Negative shift is a shift to the right */
if (shft < 0)
+ {
+ /* Protect against overflow */
+ if (shft < -VARBITMAXLEN)
+ shft = -VARBITMAXLEN;
+
PG_RETURN_DATUM(DirectFunctionCall2(bitshiftright,
VarBitPGetDatum(arg),
Int32GetDatum(-shft)));
+ }
result = (VarBit *) palloc(VARSIZE(arg));
SET_VARSIZE(result, VARSIZE(arg));
@@ -1447,9 +1453,15 @@ bitshiftright(PG_FUNCTION_ARGS)
/* Negative shift is a shift to the left */
if (shft < 0)
+ {
+ /* Protect against overflow */
+ if (shft < -VARBITMAXLEN)
+ shft = -VARBITMAXLEN;
+
PG_RETURN_DATUM(DirectFunctionCall2(bitshiftleft,
VarBitPGetDatum(arg),
Int32GetDatum(-shft)));
+ }
result = (VarBit *) palloc(VARSIZE(arg));
SET_VARSIZE(result, VARSIZE(arg));
--
2.9.3
Andreas Seltenreich <seltenreich@gmx.de> writes:
> sqlsmith just found another crasher:
> select bit '1' >> (-2^31)::int;
Nice catch :-)
> This is due to an integer overflow in bitshiftright()/bitshiftleft()
> leading to them recursively calling each other. Patch attached.
Seems sane, though I wonder if it'd be better to use -INT_MAX rather
than -VARBITMAXLEN.
regards, tom lane
Tom Lane writes: >> This is due to an integer overflow in bitshiftright()/bitshiftleft() >> leading to them recursively calling each other. Patch attached. > > Seems sane, though I wonder if it'd be better to use -INT_MAX rather > than -VARBITMAXLEN. I am undecided between those two. -INT_MAX might be a more precise fix for the problem, but the extra distance to the danger zone was kind of soothing :-). regards, Andreas
Andreas Seltenreich <seltenreich@gmx.de> writes:
> Tom Lane writes:
>> Seems sane, though I wonder if it'd be better to use -INT_MAX rather
>> than -VARBITMAXLEN.
> I am undecided between those two. -INT_MAX might be a more precise fix
> for the problem, but the extra distance to the danger zone was kind of
> soothing :-).
Yeah, might as well use the tighter limit.
Poking around in varbit.c, I noticed some other places that were assuming
that a typmod couldn't exceed VARBITMAXLEN. anybit_typmodin() enforces
that, but there are places where a user can shove in an arbitrary integer,
eg
regression=# select "bit"(42, 2147483647);
ERROR: invalid memory alloc request size 18446744073441116169
I fixed those too and pushed it. Thanks for the report!
regards, tom lane
On Fri, Oct 14, 2016 at 3:31 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote: > Andreas Seltenreich <seltenreich@gmx.de> writes: >> Tom Lane writes: >>> Seems sane, though I wonder if it'd be better to use -INT_MAX rather >>> than -VARBITMAXLEN. > >> I am undecided between those two. -INT_MAX might be a more precise fix >> for the problem, but the extra distance to the danger zone was kind of >> soothing :-). > > Yeah, might as well use the tighter limit. > > Poking around in varbit.c, I noticed some other places that were assuming > that a typmod couldn't exceed VARBITMAXLEN. anybit_typmodin() enforces > that, but there are places where a user can shove in an arbitrary integer, > eg > > regression=# select "bit"(42, 2147483647); > ERROR: invalid memory alloc request size 18446744073441116169 > > I fixed those too and pushed it. Thanks for the report! Curious -- are there real world scenarios where this would happen? merlin
Merlin Moncure <mmoncure@gmail.com> writes:
> On Fri, Oct 14, 2016 at 3:31 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Poking around in varbit.c, I noticed some other places that were assuming
>> that a typmod couldn't exceed VARBITMAXLEN.
> Curious -- are there real world scenarios where this would happen?
I think you'd have to be intentionally trying to break it. The largest
varbit typmod you're allowed to declare normally is only ~ 80 million.
regards, tom lane