Re: [PATCH] bcache: Fix a NULL or wild pointer dereference in btree_gc_rewrite_node()

[Coly Li]

On 1/28/22 6:17 PM, Greg KH wrote:
> On Tue, Jan 25, 2022 at 12:47:01AM +0800, Zhou Qingyang wrote:
> > In btree_gc_rewrite_node(), btree_node_alloc_replacement() is assigned to
> > n and return error code or NULL on failure. n is passed to
> > bch_btree_node_write_sync() and there is a dereference of it in
> > bch_btree_node_write_sync() without checks, which may lead to wild
> > pointer dereference or NULL pointer dereference depending on n.
> >
> > Fix this bug by adding IS_ERR_OR_NULL check of n.
> >
> > This bug was found by a static analyzer.
> >
> > Builds with 'make allyesconfig' show no new warnings,
> > and our static analyzer no longer warns about this code.
> >
> > Fixes: ("bcache: Rework btree cache reserve handling")
> > Signed-off-by: Zhou Qingyang <zhou1615@xxxxxxx>
> > ---
> > The analysis employs differential checking to identify inconsistent
> > security operations (e.g., checks or kfrees) between two code paths
> > and confirms that the inconsistent operations are not recovered in the
> > current function or the callers, so they constitute bugs.
> >
> > Note that, as a bug found by static analysis, it can be a false
> > positive or hard to trigger. Multiple researchers have cross-reviewed
> > the bug.
> >
> >   drivers/md/bcache/btree.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> > index 88c573eeb598..06d42292e86c 100644
> > --- a/drivers/md/bcache/btree.c
> > +++ b/drivers/md/bcache/btree.c
> > @@ -1504,6 +1504,8 @@ static int btree_gc_rewrite_node(struct btree *b, struct btree_op *op,
> >   		return 0;
> >   
> >   	n = btree_node_alloc_replacement(replace, NULL);
> > +	if (IS_ERR_OR_NULL(n))
> > +		return 0;
> >   
> >   	/* recheck reserve after allocating replacement node */
> >   	if (btree_check_reserve(b, NULL)) {
> > --
> > 2.25.1
> As stated before, umn.edu is still not allowed to contribute to the
> Linux kernel.  Please work with your administration to resolve this
> issue.

Copied. Thanks for the reminding.

Coly Li