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

[Coly Li <colyli@suse.de>]

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@umn.edu>
>> ---
>> 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