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Fix edge-case for xl_tot_len broken by bae868ca.

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bae868ca removed a check that was still needed.  If you had an
xl_tot_len at the end of a page that was too small for a record header,
but not big enough to span onto the next page, we'd immediately perform
the CRC check using a bogus large length.  Because of arbitrary coding
differences between the CRC implementations on different platforms,
nothing very bad happened on common modern systems.  On systems using
the _sb8.c fallback we could segfault.

Restore that check, add a new assertion and supply a test for that case.
Back-patch to 12, like bae868ca.

Tested-by: Tom Lane <tgl@sss.pgh.pa.us>
Tested-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGLCkTT7zYjzOxuLGahBdQ%3DMcF%3Dz5ZvrjSOnW4EDhVjT-g%40mail.gmail.com
This commit is contained in:
Thomas Munro 2023-09-26 09:07:26 +13:00
parent d1c76fdec3
commit 45d1fe8b53
2 changed files with 24 additions and 0 deletions
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11
src/backend/access/transam/xlogreader.c
View File

@ -380,6 +380,15 @@ restart:
}
else
{
/* There may be no next page if it's too small. */
if (total_len < SizeOfXLogRecord)
{
report_invalid_record(state,
"invalid record length at %X/%X: wanted %u, got %u",
(uint32) (RecPtr >> 32), (uint32) RecPtr,
(uint32) SizeOfXLogRecord, total_len);
goto err;
}
/* We'll validate the header once we have the next page. */
gotheader = false;
}
@ -795,6 +804,8 @@ ValidXLogRecord(XLogReaderState *state, XLogRecord *record, XLogRecPtr recptr)
{
pg_crc32c crc;
Assert(record->xl_tot_len >= SizeOfXLogRecord);
/* Calculate the CRC */
INIT_CRC32C(crc);
COMP_CRC32C(crc, ((char *) record) + SizeOfXLogRecord, record->xl_tot_len - SizeOfXLogRecord);

13
src/test/recovery/t/039_end_of_wal.pl
View File

@ -287,6 +287,19 @@ ok( $node->log_contains(
$log_size),
"xl_tot_len short");
# xl_tot_len in final position, not big enough to span into a new page but
# also not eligible for regular record header validation
emit_message($node, 0);
$end_lsn = advance_to_record_splitting_zone($node);
$node->stop('immediate');
write_wal($node, $TLI, $end_lsn, build_record_header(1));
$log_size = -s $node->logfile;
$node->start;
ok( $node->log_contains(
"invalid record length at .*: wanted 24, got 1", $log_size
),
"xl_tot_len short at end-of-page");
# Need more pages, but xl_prev check fails first.
emit_message($node, 0);
$end_lsn = advance_out_of_record_splitting_zone($node);