Re: pgsql: Make escaping functions retain trailing bytes of an invalid char

On 15.02.25 22:20, Tom Lane wrote:
> Make escaping functions retain trailing bytes of an invalid character.
> 
> Instead of dropping the trailing byte(s) of an invalid or incomplete
> multibyte character, replace only the first byte with a known-invalid
> sequence, and process the rest normally.  This seems less likely to
> confuse incautious callers than the behavior adopted in 5dc1e42b4.
> 
> While we're at it, adjust PQescapeStringInternal to produce at most
> one bleat about invalid multibyte characters per string.  This
> matches the behavior of PQescapeInternal, and avoids the risk of
> producing tons of repetitive junk if a long string is simply given
> in the wrong encoding.
> 
> This is a followup to the fixes for CVE-2025-1094, and should be
> included if cherry-picking those fixes.
> 
> Author: Andres Freund <andres@anarazel.de>
> Co-authored-by: Tom Lane <tgl@sss.pgh.pa.us>
> Reported-by: Jeff Davis <pgsql@j-davis.com>
> Discussion: https://postgr.es/m/20250215012712.45@rfd.leadboat.com
> Backpatch-through: 13
> 
> Branch
> ------
> REL_15_STABLE
> 
> Details
> -------
> https://git.postgresql.org/pg/commitdiff/e782a63ccb76a8db476abb8f5d96397806e3e51b
> 
> Modified Files
> --------------
> src/fe_utils/string_utils.c    | 91 ++++++++++++++++--------------------------
> src/interfaces/libpq/fe-exec.c | 73 +++++++++++++++------------------
> 2 files changed, 67 insertions(+), 97 deletions(-)

I think the backpatch of this to PG15 and older has erroneously dropped
newlines at the end of some error messages.  (libpq in newer PG uses
libpq_append_conn_error() etc. and does not have newlines in error
message strings anymore.)  I think this fix would be appropriate for
PG15 and older:

diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 4a4731d048c..73c3a0f9025 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -4040,10 +4040,10 @@ PQescapeStringInternal(PGconn *conn,
              {
                  if (remaining < charlen)
                      appendPQExpBufferStr(&conn->errorMessage,
-                                         libpq_gettext("incomplete multibyte character"));
+                                         libpq_gettext("incomplete multibyte character\n"));
                  else
                      appendPQExpBufferStr(&conn->errorMessage,
-                                         libpq_gettext("invalid multibyte character"));
+                                         libpq_gettext("invalid multibyte character\n"));
                  /* Issue a complaint only once per string */
                  already_complained = true;
              }