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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 881defde94
commit 10d0591ea2
2 changed files with 24 additions and 0 deletions
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11
src/backend/access/transam/xlogreader.c
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@ -653,6 +653,15 @@ 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: expected at least %u, got %u",
LSN_FORMAT_ARGS(RecPtr),
(uint32) SizeOfXLogRecord, total_len);
goto err;
}
/* We'll validate the header once we have the next page. */
gotheader = false;
}
@ -1190,6 +1199,8 @@ 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);