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Handle unaligned SerializeSnapshot() buffer.

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Likewise in RestoreSnapshot().  Do so by copying between the user buffer
and a stack buffer of known alignment.  Back-patch to 9.6, where this
last applies cleanly.  In master, the select_parallel test dies with
SIGBUS on "Oracle Solaris 10 1/13 s10s_u11wos_24a SPARC", building
32-bit with gcc 4.9.2.  In 9.6 and 9.5, the buffers in question happen
to be sufficiently-aligned, and this change is mere insurance against
future 9.6 changes or extension code compromising that.
This commit is contained in:
Noah Misch
2017-03-02 00:03:27 -05:00
parent 4461a9bfd1
commit 7f3112135e
1 changed files with 40 additions and 36 deletions
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76
src/backend/utils/time/snapmgr.c
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@ -2015,34 +2015,37 @@ EstimateSnapshotSpace(Snapshot snap)
void void
SerializeSnapshot(Snapshot snapshot, char *start_address) SerializeSnapshot(Snapshot snapshot, char *start_address)
{ {
SerializedSnapshotData *serialized_snapshot; SerializedSnapshotData serialized_snapshot;
Assert(snapshot->subxcnt >= 0); Assert(snapshot->subxcnt >= 0);
serialized_snapshot = (SerializedSnapshotData *) start_address;
/* Copy all required fields */ /* Copy all required fields */
serialized_snapshot->xmin = snapshot->xmin; serialized_snapshot.xmin = snapshot->xmin;
serialized_snapshot->xmax = snapshot->xmax; serialized_snapshot.xmax = snapshot->xmax;
serialized_snapshot->xcnt = snapshot->xcnt; serialized_snapshot.xcnt = snapshot->xcnt;
serialized_snapshot->subxcnt = snapshot->subxcnt; serialized_snapshot.subxcnt = snapshot->subxcnt;
serialized_snapshot->suboverflowed = snapshot->suboverflowed; serialized_snapshot.suboverflowed = snapshot->suboverflowed;
serialized_snapshot->takenDuringRecovery = snapshot->takenDuringRecovery; serialized_snapshot.takenDuringRecovery = snapshot->takenDuringRecovery;
serialized_snapshot->curcid = snapshot->curcid; serialized_snapshot.curcid = snapshot->curcid;
serialized_snapshot->whenTaken = snapshot->whenTaken; serialized_snapshot.whenTaken = snapshot->whenTaken;
serialized_snapshot->lsn = snapshot->lsn; serialized_snapshot.lsn = snapshot->lsn;
/* /*
* Ignore the SubXID array if it has overflowed, unless the snapshot was * Ignore the SubXID array if it has overflowed, unless the snapshot was
* taken during recovey - in that case, top-level XIDs are in subxip as * taken during recovey - in that case, top-level XIDs are in subxip as
* well, and we mustn't lose them. * well, and we mustn't lose them.
*/ */
if (serialized_snapshot->suboverflowed && !snapshot->takenDuringRecovery) if (serialized_snapshot.suboverflowed && !snapshot->takenDuringRecovery)
serialized_snapshot->subxcnt = 0; serialized_snapshot.subxcnt = 0;
/* Copy struct to possibly-unaligned buffer */
memcpy(start_address,
&serialized_snapshot, sizeof(SerializedSnapshotData));
/* Copy XID array */ /* Copy XID array */
if (snapshot->xcnt > 0) if (snapshot->xcnt > 0)
memcpy((TransactionId *) (serialized_snapshot + 1), memcpy((TransactionId *) (start_address +
sizeof(SerializedSnapshotData)),
snapshot->xip, snapshot->xcnt * sizeof(TransactionId)); snapshot->xip, snapshot->xcnt * sizeof(TransactionId));
/* /*
@ -2051,12 +2054,12 @@ SerializeSnapshot(Snapshot snapshot, char *start_address)
* snapshot taken during recovery; all the top-level XIDs are in subxip as * snapshot taken during recovery; all the top-level XIDs are in subxip as
* well in that case, so we mustn't lose them. * well in that case, so we mustn't lose them.
*/ */
if (serialized_snapshot->subxcnt > 0) if (serialized_snapshot.subxcnt > 0)
{ {
Size subxipoff = sizeof(SerializedSnapshotData) + Size subxipoff = sizeof(SerializedSnapshotData) +
snapshot->xcnt * sizeof(TransactionId); snapshot->xcnt * sizeof(TransactionId);
memcpy((TransactionId *) ((char *) serialized_snapshot + subxipoff), memcpy((TransactionId *) (start_address + subxipoff),
snapshot->subxip, snapshot->subxcnt * sizeof(TransactionId)); snapshot->subxip, snapshot->subxcnt * sizeof(TransactionId));
} }
} }
@ -2071,50 +2074,51 @@ SerializeSnapshot(Snapshot snapshot, char *start_address)
Snapshot Snapshot
RestoreSnapshot(char *start_address) RestoreSnapshot(char *start_address)
{ {
SerializedSnapshotData *serialized_snapshot; SerializedSnapshotData serialized_snapshot;
Size size; Size size;
Snapshot snapshot; Snapshot snapshot;
TransactionId *serialized_xids; TransactionId *serialized_xids;
serialized_snapshot = (SerializedSnapshotData *) start_address; memcpy(&serialized_snapshot, start_address,
sizeof(SerializedSnapshotData));
serialized_xids = (TransactionId *) serialized_xids = (TransactionId *)
(start_address + sizeof(SerializedSnapshotData)); (start_address + sizeof(SerializedSnapshotData));
/* We allocate any XID arrays needed in the same palloc block. */ /* We allocate any XID arrays needed in the same palloc block. */
size = sizeof(SnapshotData) size = sizeof(SnapshotData)
+ serialized_snapshot->xcnt * sizeof(TransactionId) + serialized_snapshot.xcnt * sizeof(TransactionId)
+ serialized_snapshot->subxcnt * sizeof(TransactionId); + serialized_snapshot.subxcnt * sizeof(TransactionId);
/* Copy all required fields */ /* Copy all required fields */
snapshot = (Snapshot) MemoryContextAlloc(TopTransactionContext, size); snapshot = (Snapshot) MemoryContextAlloc(TopTransactionContext, size);
snapshot->satisfies = HeapTupleSatisfiesMVCC; snapshot->satisfies = HeapTupleSatisfiesMVCC;
snapshot->xmin = serialized_snapshot->xmin; snapshot->xmin = serialized_snapshot.xmin;
snapshot->xmax = serialized_snapshot->xmax; snapshot->xmax = serialized_snapshot.xmax;
snapshot->xip = NULL; snapshot->xip = NULL;
snapshot->xcnt = serialized_snapshot->xcnt; snapshot->xcnt = serialized_snapshot.xcnt;
snapshot->subxip = NULL; snapshot->subxip = NULL;
snapshot->subxcnt = serialized_snapshot->subxcnt; snapshot->subxcnt = serialized_snapshot.subxcnt;
snapshot->suboverflowed = serialized_snapshot->suboverflowed; snapshot->suboverflowed = serialized_snapshot.suboverflowed;
snapshot->takenDuringRecovery = serialized_snapshot->takenDuringRecovery; snapshot->takenDuringRecovery = serialized_snapshot.takenDuringRecovery;
snapshot->curcid = serialized_snapshot->curcid; snapshot->curcid = serialized_snapshot.curcid;
snapshot->whenTaken = serialized_snapshot->whenTaken; snapshot->whenTaken = serialized_snapshot.whenTaken;
snapshot->lsn = serialized_snapshot->lsn; snapshot->lsn = serialized_snapshot.lsn;
/* Copy XIDs, if present. */ /* Copy XIDs, if present. */
if (serialized_snapshot->xcnt > 0) if (serialized_snapshot.xcnt > 0)
{ {
snapshot->xip = (TransactionId *) (snapshot + 1); snapshot->xip = (TransactionId *) (snapshot + 1);
memcpy(snapshot->xip, serialized_xids, memcpy(snapshot->xip, serialized_xids,
serialized_snapshot->xcnt * sizeof(TransactionId)); serialized_snapshot.xcnt * sizeof(TransactionId));
} }
/* Copy SubXIDs, if present. */ /* Copy SubXIDs, if present. */
if (serialized_snapshot->subxcnt > 0) if (serialized_snapshot.subxcnt > 0)
{ {
snapshot->subxip = ((TransactionId *) (snapshot + 1)) + snapshot->subxip = ((TransactionId *) (snapshot + 1)) +
serialized_snapshot->xcnt; serialized_snapshot.xcnt;
memcpy(snapshot->subxip, serialized_xids + serialized_snapshot->xcnt, memcpy(snapshot->subxip, serialized_xids + serialized_snapshot.xcnt,
serialized_snapshot->subxcnt * sizeof(TransactionId)); serialized_snapshot.subxcnt * sizeof(TransactionId));
} }
/* Set the copied flag so that the caller will set refcounts correctly. */ /* Set the copied flag so that the caller will set refcounts correctly. */