Don't get confused if a WAL partial record header has xl_tot_len == 0.

If a WAL record header was split across pages, but xl_tot_len was 0, we
would get confused and conclude that we had already read the whole record,
and proceed to CRC check it. That can lead to a crash in RecordIsValid(),
which isn't careful to not read beyond end-of-record, as defined by
xl_tot_len.

Add an explicit sanity check for xl_tot_len <= SizeOfXlogRecord. Also,
make RecordIsValid() more robust by checking in each step that it doesn't
try to access memory beyond end of record, even if a length field in the
record's or a backup block's header is bogus.

Per report and analysis by Tom Lane.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index efda4634d560c046f27aa9dbfcd953f1409eee9a..f24e2fb63e943bb93c04d46ee37a4454224c642e 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3707,8 +3707,17 @@ RecordIsValid(XLogRecord *record, XLogRecPtr recptr, int emode)
    uint32      len = record->xl_len;
    BkpBlock    bkpb;
    char       *blk;
+   char       *recend = (char *) record + record->xl_tot_len;
 
    /* First the rmgr data */
+   if (XLogRecGetData(record) + len > recend)
+   {
+       /* ValidXLogRecordHeader() should've caught this already... */
+       ereport(emode_for_corrupt_record(emode, recptr),
+               (errmsg("invalid record length at %X/%X",
+                       (uint32) (recptr >> 32), (uint32) recptr)));
+       return false;
+   }
    INIT_CRC32(crc);
    COMP_CRC32(crc, XLogRecGetData(record), len);
 
@@ -3721,7 +3730,15 @@ RecordIsValid(XLogRecord *record, XLogRecPtr recptr, int emode)
        if (!(record->xl_info & XLR_SET_BKP_BLOCK(i)))
            continue;
 
+       if (blk + sizeof(BkpBlock) > recend)
+       {
+           ereport(emode_for_corrupt_record(emode, recptr),
+                   (errmsg("incorrect backup block size in record at %X/%X",
+                           (uint32) (recptr >> 32), (uint32) recptr)));
+           return false;
+       }
        memcpy(&bkpb, blk, sizeof(BkpBlock));
+
        if (bkpb.hole_offset + bkpb.hole_length > BLCKSZ)
        {
            ereport(emode_for_corrupt_record(emode, recptr),
@@ -3730,6 +3747,14 @@ RecordIsValid(XLogRecord *record, XLogRecPtr recptr, int emode)
            return false;
        }
        blen = sizeof(BkpBlock) + BLCKSZ - bkpb.hole_length;
+
+       if (blk + blen > recend)
+       {
+           ereport(emode_for_corrupt_record(emode, recptr),
+                   (errmsg("invalid backup block size in record at %X/%X",
+                           (uint32) (recptr >> 32), (uint32) recptr)));
+           return false;
+       }
        COMP_CRC32(crc, blk, blen);
        blk += blen;
    }
@@ -3879,8 +3904,8 @@ retry:
 
    /*
     * If the whole record header is on this page, validate it immediately.
-    * Otherwise validate it after reading the rest of the header from next
-    * page.
+    * Otherwise only do a basic sanity check on xl_tot_len, and validate the
+    * rest of the header after reading it from the next page.
     */
    if (targetRecOff <= XLOG_BLCKSZ - SizeOfXLogRecord)
    {
@@ -3889,7 +3914,16 @@ retry:
        gotheader = true;
    }
    else
+   {
+       if (total_len < SizeOfXLogRecord)
+       {
+           ereport(emode_for_corrupt_record(emode, *RecPtr),
+                   (errmsg("invalid record length at %X/%X",
+                           (uint32) ((*RecPtr) >> 32), (uint32) *RecPtr)));
+           goto next_record_is_invalid;
+       }
        gotheader = false;
+   }
 
    /*
     * Allocate or enlarge readRecordBuf as needed.  To avoid useless small