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SubjectRe: [PATCH] afs: Fix poential UAF in afs_make_call
Date
Zheng Wang <zyytlz.wz@163.com> wrote:

> There is a function call : afs_fs_get_capabilities calls afs_make_call, in
> afs_make_call, if error occurs in rxrpc_kernel_send_data, it will call
> afs_put_call twice, which will free the call. And the access of
> call->state will trigger a use-after-free bug.

Are you sure of that? Did you actually trigger a UAF?

> - if (cancel_work_sync(&call->async_work))
> - afs_put_call(call);
> + cancel_work_sync(&call->async_work);

The problem with this change is that it will leak a ref if the work item was
queued but gets cancelled before being run, given to it here:

static void afs_wake_up_async_call(struct sock *sk, struct rxrpc_call *rxcall,
unsigned long call_user_ID)
{
struct afs_call *call = (struct afs_call *)call_user_ID;
int r;

trace_afs_notify_call(rxcall, call);
call->need_attention = true;

if (__refcount_inc_not_zero(&call->ref, &r)) { <----
trace_afs_call(call->debug_id, afs_call_trace_wake, r + 1,
atomic_read(&call->net->nr_outstanding_calls),
__builtin_return_address(0));

if (!queue_work(afs_async_calls, &call->async_work))
afs_put_call(call);
}
}

I *think* that cancel_work_sync() returns false if the work item is executing,
but hasn't been requeued.

David

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