High [CVE-2026-74631] fix splice entry lifetime imbalance in smc_rx_splice

In the Linux kernel, the following vulnerability has been resolved: net: smc: fix splice entry lifetime imbalance in smc_rx_splice smc_rx_splice() passes pages to splice_to_pipe() before taking the references that cover the lifetime of each splice entry.

In the VM-backed RMB path, splice_to_pipe() may drop unqueued entries through smc_rx_spd_release(), while queued entries are released later via the pipe buffer callback.

The old post-splice accounting also derives the number of queued VM pages from an offset mutated while building the descriptor, and a multi-page splice pairs one sock_hold() with multiple sock_put() calls.

Take the page and socket references for every candidate entry before splice_to_pipe(), and drop the matching private state, page reference, and socket reference from smc_rx_spd_release() for entries that never get queued. This fixes a refcount imbalance that can underflow page refcounts and trigger a use-after-free.

This vulnerability arises from an imbalance in the lifetime management of splice entries, where page references are not properly handled before being passed to `splice_to_pipe()`. This can lead to a reference count underflow, resulting in a use-after-free condition.

A successful exploitation of this flaw could potentially lead to arbitrary code execution or a denial of service.