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 42792b7f0b6f8aa5846fd2addbec057382e1fcf7..0986c50c76ed2fbc8020c49182f95e1a42e56e3f 100644 (file)
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -4983,13 +4983,20 @@ 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 ced7980709fe4688dc3974134fc056d7e6683875..6400bcb525491e4b2482914243d417530a3985cc 100644 (file)
--- a/src/test/regress/expected/numeric.out
+++ b/src/test/regress/expected/numeric.out
@@ -1266,6 +1266,12 @@ SELECT '' AS to_char_26, 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 '' AS to_char_27, to_char('100'::numeric, 'foo999');
  to_char_27 | to_char 

diff --git a/src/test/regress/sql/numeric.sql b/src/test/regress/sql/numeric.sql
index e5ff2b59029c035a7eb19d16d0c8ac3b8869e87d..9924419a57748d28bc1e844c8c65fac7055a3dd7 100644 (file)
--- a/src/test/regress/sql/numeric.sql
+++ b/src/test/regress/sql/numeric.sql
@@ -799,6 +799,7 @@ SELECT '' AS to_char_23, to_char(val, '9.999EEEE')              FROM num_data;
 SELECT '' AS to_char_24, to_char('100'::numeric, 'FM999.9');
 SELECT '' AS to_char_25, to_char('100'::numeric, 'FM999.');
 SELECT '' AS to_char_26, to_char('100'::numeric, 'FM999');
+SELECT to_char('12345678901'::float8, 'FM9999999999D9999900000000000000000');
 
 -- Check parsing of literal text in a format string
 SELECT '' AS to_char_27, to_char('100'::numeric, 'foo999');