From: Tom Lane <tgl@sss.pgh.pa.us>
To: thiagotnunes@gmail.com
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17839: Heap-buffer overflow on float8_to_char with invalid template
Date: Tue, 14 Mar 2023 18:49:05 -0400
Message-ID: <3011659.1678834145@sss.pgh.pa.us> (raw)
In-Reply-To: <17839-aada50db24d7b0da@postgresql.org>
References: <17839-aada50db24d7b0da@postgresql.org>
PG Bug reporting form <noreply@postgresql.org> writes:
> Heap-buffer overflow on float8_to_char when format exceeds max double
> digits. I noticed this when running tests with memory sanitiser (msan).
> The following example triggers the failure (considering max double digits
> `DBL_DIG` is 15):
> float8_to_char(12345678901, "FM9999999999D999990")
Thanks for the report! For reasons that aren't entirely clear to me,
valgrind didn't whine about this until I added a few more zeroes to the
format string, like
SELECT to_char('12345678901'::float8, 'FM9999999999D9999900000000000000000');
Nonetheless, it did see the issue at that point. I'm inclined to fix
it by making the code that adjusts Np->last_relevant more paranoid,
as attached.
regards, tom lane
Attachments:fix-wild-read-in-to_char.patch (text/x-diff, 2.1K) downloaddiff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.cindex f3f4db5ef6..e6246dc44b 100644--- a/src/backend/utils/adt/formatting.c+++ b/src/backend/utils/adt/formatting.c@@ -5695,13 +5695,20 @@ NUM_processor(FormatNode *node, NUMDesc *Num, char *inout,
/*
* If any '0' specifiers are present, make sure we don't strip
- * those digits.+ * those digits. But don't advance last_relevant beyond the last+ * character of the Np->number string, which is a hazard if the+ * number got shortened due to precision limitations.
*/
if (Np->last_relevant && Np->Num->zero_end > Np->out_pre_spaces)
{
+ int last_zero_pos;
char *last_zero;
- last_zero = Np->number + (Np->Num->zero_end - Np->out_pre_spaces);+ /* note that Np->number cannot be zero-length here */+ last_zero_pos = strlen(Np->number) - 1;+ last_zero_pos = Min(last_zero_pos,+ Np->Num->zero_end - Np->out_pre_spaces);+ last_zero = Np->number + last_zero_pos;
if (Np->last_relevant < last_zero)
Np->last_relevant = last_zero;
}
diff --git a/src/test/regress/expected/numeric.out b/src/test/regress/expected/numeric.outindex 2ac2c99b19..26930f4db4 100644--- a/src/test/regress/expected/numeric.out+++ b/src/test/regress/expected/numeric.out@@ -1929,6 +1929,12 @@ SELECT to_char('100'::numeric, 'FM999');
100
(1 row)
+SELECT to_char('12345678901'::float8, 'FM9999999999D9999900000000000000000');+ to_char +-----------------+ ##########.####+(1 row)+
-- Check parsing of literal text in a format string
SELECT to_char('100'::numeric, 'foo999');
to_char
diff --git a/src/test/regress/sql/numeric.sql b/src/test/regress/sql/numeric.sqlindex 6e9e6145d0..2dddb58625 100644--- a/src/test/regress/sql/numeric.sql+++ b/src/test/regress/sql/numeric.sql@@ -979,6 +979,7 @@ FROM v;
SELECT to_char('100'::numeric, 'FM999.9');
SELECT to_char('100'::numeric, 'FM999.');
SELECT to_char('100'::numeric, 'FM999');
+SELECT to_char('12345678901'::float8, 'FM9999999999D9999900000000000000000');
-- Check parsing of literal text in a format string
SELECT to_char('100'::numeric, 'foo999');
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, thiagotnunes@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17839: Heap-buffer overflow on float8_to_char with invalid template
In-Reply-To: <3011659.1678834145@sss.pgh.pa.us>
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