sched_ext: bpf_iter_scx_dsq_new() should always initialize iterator

BPF programs may call next() and destroy() on BPF iterators even after new()
returns an error value (e.g. bpf_for_each() macro ignores error returns from
new()). bpf_iter_scx_dsq_new() could leave the iterator in an uninitialized
state after an error return causing bpf_iter_scx_dsq_next() to dereference
garbage data. Make bpf_iter_scx_dsq_new() always clear $kit->dsq so that
next() and destroy() become noops.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 650ba21b131e ("sched_ext: Implement DSQ iterator")
Cc: stable@vger.kernel.org # v6.12+
Acked-by: Andrea Righi <arighi@nvidia.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 4e37b40ce280cb017e38d20ae6673a85d4ba0952..f5133249fd4d92e362fe032473e4aace7689ef5b 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -6827,6 +6827,12 @@ __bpf_kfunc int bpf_iter_scx_dsq_new(struct bpf_iter_scx_dsq *it, u64 dsq_id,
        BUILD_BUG_ON(__alignof__(struct bpf_iter_scx_dsq_kern) !=
                     __alignof__(struct bpf_iter_scx_dsq));
 
+       /*
+        * next() and destroy() will be called regardless of the return value.
+        * Always clear $kit->dsq.
+        */
+       kit->dsq = NULL;
+
        if (flags & ~__SCX_DSQ_ITER_USER_FLAGS)
                return -EINVAL;