Il giorno 23 mag 2017, alle ore 22:52, Gustavo A. R. Silva =

[off-list ref] ha scritto:

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Hello everybody,
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Hi

While looking into Coverity ID 1408828 I ran into the following piece =

of code at block/bfq-wf2q.c:542:

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542static struct rb_node *bfq_find_deepest(struct rb_node *node)
543{
544        struct rb_node *deepest;
545
546        if (!node->rb_right && !node->rb_left)
547                deepest =3D rb_parent(node);
548        else if (!node->rb_right)
549                deepest =3D node->rb_left;
550        else if (!node->rb_left)
551                deepest =3D node->rb_right;
552        else {
553                deepest =3D rb_next(node);
554                if (deepest->rb_right)
555                        deepest =3D deepest->rb_right;
556                else if (rb_parent(deepest) !=3D node)
557                        deepest =3D rb_parent(deepest);
558        }
559
560        return deepest;
561}
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The issue here is that there is a potential NULL pointer dereference =

at line 554, in case function rb_next() returns NULL.

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Can rb_next(node) return NULL, although node is guaranteed to have both
a left and a right child at line 554?

Thanks,
Paolo

Maybe a patch like the following could be applied in order to avoid =

any chance of a NULL pointer dereference:

rb_node *node)

               deepest =3D node->rb_right;
       else {
               deepest =3D rb_next(node);
+               if (!deepest)
+                       return NULL;
               if (deepest->rb_right)
                       deepest =3D deepest->rb_right;
               else if (rb_parent(deepest) !=3D node)
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What do you think?
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I'd really appreciate any comment on this.
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Thank you!
--
Gustavo A. R. Silva
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