CVE-2023-52447

In the Linux kernel, the following vulnerability has been resolved:

bpf: Defer the free of inner map when necessary

When updating or deleting an inner map in map array or map htab, the map may still be accessed by non-sleepable program or sleepable program. However bpfmapfdputptr() decreases the ref-counter of the inner map directly through bpfmapput(), if the ref-counter is the last one (which is true for most cases), the inner map will be freed by ops->mapfree() in a kworker. But for now, most .mapfree() callbacks don't use synchronizercu() or its variants to wait for the elapse of a RCU grace period, so after the invocation of ops->mapfree completes, the bpf program which is accessing the inner map may incur use-after-free problem.

Fix the free of inner map by invoking bpfmapfreedeferred() after both one RCU grace period and one tasks trace RCU grace period if the inner map has been removed from the outer map before. The deferment is accomplished by using callrcu() or callrcutaskstrace() when releasing the last ref-counter of bpf map. The newly-added rcuhead field in bpfmap shares the same storage space with work field to reduce the size of bpfmap.