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

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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
This commit is contained in:
Tom Lane
2023-03-14 19:17:31 -04:00
parent a563c24c95
commit b081fe4199
3 changed files with 16 additions and 2 deletions
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11
src/backend/utils/adt/formatting.c
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@ -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;
}