Bug 2521413 (CVE-2026-74631)

Summary: CVE-2026-74631 kernel: net: smc: fix splice entry lifetime imbalance in smc_rx_splice
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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OS: Linux   
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A flaw was found in the Linux kernel's `smc_rx_splice` function within the net: smc component. 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.
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Description OSIDB Bzimport 2026-08-22 15:44:23 UTC 
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.
Comment 1 Mauro Matteo Cascella 2026-08-24 12:37:11 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082221-CVE-2026-74631-4134@gregkh/T