Fix corner case bug in numeric to_char() some more.

The band-aid applied in commit f0bedf3e4 turns out to still need
some work: it made sure we didn't set Np->last_relevant too small
(to the left of the decimal point), but it didn't prevent setting
it too large (off the end of the partially-converted string).
This could result in fetching data beyond the end of the allocated
space, which with very bad luck could cause a SIGSEGV, though
I don't see any hazard of interesting memory disclosure.

Per bug #17839 from Thiago Nunes.  The bug's pretty ancient,
so back-patch to all supported versions.

Discussion: https://postgr.es/m/17839-aada50db24d7b0da@postgresql.org

diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index f3f4db5ef6066dc3d79fd5cd4cf78585c72d059e..e6246dc44bdfc52b5776490b4fde6be6bba369d5 100644 (file)
--- 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.out
index 2ac2c99b1962d6108e25166bea9f8cd1a5a57405..26930f4db4713af08749a13bfd8260405bcd1302 100644 (file)
--- 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.sql
index 6e9e6145d03889f10f6edc4ff70c59e9ba185f53..2dddb5862552ed856763d2b6bccf1467ad5be6e3 100644 (file)
--- 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');