From f4cc40351f56fdb6eaa4531c85677e80ea6feaf5 Mon Sep 17 00:00:00 2001 From: Matthias van de Meent Date: Mon, 20 Jun 2022 10:21:22 +0200 Subject: [PATCH v4] Add protections in xlog record APIs against large numbers and overflows. Before this; it was possible for an extension to create malicious WAL records that were too large to replay; or that would overflow the xl_tot_len field, causing potential corruption in WAL record IO ops. Emitting invalid records was also possible through pg_logical_emit_message(), which allowed you to emit arbitrary amounts of data up to 2GB, much higher than the replay limit of 1GB. --- src/backend/access/transam/xloginsert.c | 62 +++++++++++++++++++++---- src/include/access/xloginsert.h | 4 +- src/include/access/xlogrecord.h | 4 ++ 3 files changed, 58 insertions(+), 12 deletions(-) diff --git a/src/backend/access/transam/xloginsert.c b/src/backend/access/transam/xloginsert.c index 2ce9be2cc7..a3387a9265 100644 --- a/src/backend/access/transam/xloginsert.c +++ b/src/backend/access/transam/xloginsert.c @@ -141,7 +141,18 @@ static XLogRecData *XLogRecordAssemble(RmgrId rmid, uint8 info, bool *topxid_included); static bool XLogCompressBackupBlock(char *page, uint16 hole_offset, uint16 hole_length, char *dest, uint16 *dlen); +static inline void XLogErrorDataLimitExceeded(); +/* + * Error due to exceeding the maximum size of a WAL record, or registering + * more datas than are being accounted for by the XLog infrastructure. + */ +static inline void +XLogErrorDataLimitExceeded() +{ + elog(ERROR, "too much WAL data"); +} + /* * Begin constructing a WAL record. This must be called before the * XLogRegister* functions and XLogInsert(). @@ -348,14 +359,24 @@ XLogRegisterBlock(uint8 block_id, RelFileNode *rnode, ForkNumber forknum, * XLogRecGetData(). */ void -XLogRegisterData(char *data, int len) +XLogRegisterData(char *data, uint32 len) { XLogRecData *rdata; - Assert(begininsert_called); + Assert(begininsert_called && AllocSizeIsValid(len)); + + /* + * Check against max_rdatas; and ensure we don't fill a record with + * more data than can be replayed. Records are allocated in one chunk, so + * ensure AllocSizeIsValid() for that size of record. + * + * We also protect against overflows by first casting to uint64 - with only + * uint32-operations this could still be an issue. + */ + if (unlikely(num_rdatas >= max_rdatas) || + unlikely(!AllocSizeIsValid((uint64) mainrdata_len + (uint64) len))) + XLogErrorDataLimitExceeded(); - if (num_rdatas >= max_rdatas) - elog(ERROR, "too much WAL data"); rdata = &rdatas[num_rdatas++]; rdata->data = data; @@ -386,12 +407,12 @@ XLogRegisterData(char *data, int len) * limited) */ void -XLogRegisterBufData(uint8 block_id, char *data, int len) +XLogRegisterBufData(uint8 block_id, char *data, uint32 len) { registered_buffer *regbuf; XLogRecData *rdata; - Assert(begininsert_called); + Assert(begininsert_called && len <= UINT16_MAX); /* find the registered buffer struct */ regbuf = ®istered_buffers[block_id]; @@ -399,8 +420,16 @@ XLogRegisterBufData(uint8 block_id, char *data, int len) elog(ERROR, "no block with id %d registered with WAL insertion", block_id); - if (num_rdatas >= max_rdatas) - elog(ERROR, "too much WAL data"); + /* + * Check against max_rdatas; and ensure we don't register more data per + * buffer than can be handled by the physical data format; + * i.e. that regbuf->rdata_len does not grow beyond what + * XLogRecordBlockHeader->data_length can hold. + */ + if (unlikely(num_rdatas >= max_rdatas) || + unlikely(regbuf->rdata_len + len > UINT16_MAX)) + XLogErrorDataLimitExceeded(); + rdata = &rdatas[num_rdatas++]; rdata->data = data; @@ -519,7 +548,7 @@ XLogRecordAssemble(RmgrId rmid, uint8 info, XLogRecPtr *fpw_lsn, int *num_fpi, bool *topxid_included) { XLogRecData *rdt; - uint32 total_len = 0; + uint64 total_len = 0; int block_id; pg_crc32c rdata_crc; registered_buffer *prev_regbuf = NULL; @@ -756,12 +785,18 @@ XLogRecordAssemble(RmgrId rmid, uint8 info, if (needs_data) { + /* + * When copying to XLogRecordBlockHeader, the length is narrowed + * to an uint16. We double-check that that is still correct. + */ + Assert(regbuf->rdata_len <= UINT16_MAX); + /* * Link the caller-supplied rdata chain for this buffer to the * overall list. */ bkpb.fork_flags |= BKPBLOCK_HAS_DATA; - bkpb.data_length = regbuf->rdata_len; + bkpb.data_length = (uint16) regbuf->rdata_len; total_len += regbuf->rdata_len; rdt_datas_last->next = regbuf->rdata_head; @@ -858,6 +893,13 @@ XLogRecordAssemble(RmgrId rmid, uint8 info, for (rdt = hdr_rdt.next; rdt != NULL; rdt = rdt->next) COMP_CRC32C(rdata_crc, rdt->data, rdt->len); + /* + * Ensure that xlogreader.c can read the record by ensuring that the + * data section of the WAL record can be allocated. + */ + if (unlikely(!AllocSizeIsValid(total_len))) + XLogErrorDataLimitExceeded(); + /* * Fill in the fields in the record header. Prev-link is filled in later, * once we know where in the WAL the record will be inserted. The CRC does diff --git a/src/include/access/xloginsert.h b/src/include/access/xloginsert.h index 5fc340c434..5ca0b0c2f0 100644 --- a/src/include/access/xloginsert.h +++ b/src/include/access/xloginsert.h @@ -43,12 +43,12 @@ extern void XLogBeginInsert(void); extern void XLogSetRecordFlags(uint8 flags); extern XLogRecPtr XLogInsert(RmgrId rmid, uint8 info); extern void XLogEnsureRecordSpace(int max_block_id, int ndatas); -extern void XLogRegisterData(char *data, int len); +extern void XLogRegisterData(char *data, uint32 len); extern void XLogRegisterBuffer(uint8 block_id, Buffer buffer, uint8 flags); extern void XLogRegisterBlock(uint8 block_id, RelFileNode *rnode, ForkNumber forknum, BlockNumber blknum, char *page, uint8 flags); -extern void XLogRegisterBufData(uint8 block_id, char *data, int len); +extern void XLogRegisterBufData(uint8 block_id, char *data, uint32 len); extern void XLogResetInsertion(void); extern bool XLogCheckBufferNeedsBackup(Buffer buffer); diff --git a/src/include/access/xlogrecord.h b/src/include/access/xlogrecord.h index 052ac6817a..3575363e84 100644 --- a/src/include/access/xlogrecord.h +++ b/src/include/access/xlogrecord.h @@ -37,6 +37,10 @@ * The XLogRecordBlockHeader, XLogRecordDataHeaderShort and * XLogRecordDataHeaderLong structs all begin with a single 'id' byte. It's * used to distinguish between block references, and the main data structs. + * + * Note that xlogreader.c limits the total size of the xl_tot_len to + * MaxAllocSize (1GB - 1). This means that this is also the maximum size + * of a single WAL record - we would be unable to replay any larger record. */ typedef struct XLogRecord { -- 2.30.2