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 78a06bb8423262e6b9e12add0ac700f1f22c54f5..7b1f080f80d83d0c8cef55cb2430587a509565c1 100644 (file)
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -5731,13 +5731,20 @@ 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 e224eff9f06f5c77a2d5abf1c53bafca930d3c70..ea11fee39b76bbd18ec53c03ddde6fcba9d75e9d 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 eeca63d86e71c86448ce8e8a7444d82f535cda5c..c54ea52a603eed2c94ba5a0adadb46c939674b9c 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');