From: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> |
---|---|
To: | ranier(dot)vf(at)gmail(dot)com |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Possible dereference null return (src/backend/replication/logical/reorderbuffer.c) |
Date: | 2021-02-12 06:56:02 |
Message-ID: | 20210212.155602.691574878609873242.horikyota.ntt@gmail.com |
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Thread: | |
Lists: | pgsql-hackers |
At Wed, 10 Feb 2021 20:12:38 -0300, Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> wrote in
> Hi,
>
> Per Coverity.
>
> If xid is a subtransaction, the setup of base snapshot on the top-level
> transaction,
> can be not optional, otherwise a Dereference null return value
> (NULL_RETURNS) can be raised.
>
> Patch suggestion to fix this.
>
> diff --git a/src/backend/replication/logical/reorderbuffer.c
> b/src/backend/replication/logical/reorderbuffer.c
> index 5a62ab8bbc..3c6a81f716 100644
> --- a/src/backend/replication/logical/reorderbuffer.c
> +++ b/src/backend/replication/logical/reorderbuffer.c
> @@ -2993,8 +2993,8 @@ ReorderBufferSetBaseSnapshot(ReorderBuffer *rb,
> TransactionId xid,
> */
> txn = ReorderBufferTXNByXid(rb, xid, true, &is_new, lsn, true);
> if (rbtxn_is_known_subxact(txn))
> - txn = ReorderBufferTXNByXid(rb, txn->toplevel_xid, false,
> - NULL, InvalidXLogRecPtr, false);
> + txn = ReorderBufferTXNByXid(rb, txn->toplevel_xid, true,
> + NULL, InvalidXLogRecPtr, true);
> Assert(txn->base_snapshot == NULL);
If the return from the first call is a subtransaction, the second call
always obtain the top transaction. If the top transaction actualy did
not exist, it's rather the correct behavior to cause SEGV, than
creating a bogus rbtxn. THus it is wrong to set create=true and
create_as_top=true. We could change the assertion like Assert (txn &&
txn->base_snapshot) to make things clearer.
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
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