Re: [PATCH] FIx explicit null dereference pointer (nbtree.c)

Em qua., 22 de abr. de 2020 às 21:24, Peter Geoghegan <pg(at)bowt(dot)ie> escreveu:

> On Wed, Apr 22, 2020 at 3:55 PM Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> wrote:
> > per Coverity.
>
> Some Postgres hackers have access to a dedicated coverity
> installation, and this issue has probably already been dismissed.
>
I will take a note.

>
> > 1. assign_zero: Assigning: opaque = NULL.
> > 2. Condition buf < 0, taking true branch.
> > 3. Condition !(((PageHeader)page)->pd_upper == 0), taking false branch.
> > 4. Condition blkno != orig_blkno, taking true branch.
> > 5. Condition _bt_page_recyclable(page), taking false branch.
> > CID 1314742 (#2 of 2): Explicit null dereferenced (FORWARD_NULL)
> > 6. var_deref_op: Dereferencing null pointer opaque.
>
> This is a false positive. btvacuumpage() is supposed to be a recursive
> function, but in practice the only caller always uses the same block
> number for both blkno and orig_blkno -- the tail recursion is actually
> implemented using goto/a loop.
>
This means that it is impossible for these conditions described by Coverity
to happen on the first call, when the var opaque is NULL.

regards,
Ranier Vilela