Bug 2517059 (CVE-2026-74493)

Summary: CVE-2026-74493 kernel: net/smc: fix socket use-after-free during link group termination
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's net/smc component. A use-after-free vulnerability occurs during link group termination when a concurrent close operation unregisters a connection and frees its socket before the termination worker can properly hold the socket. This race condition can lead to a system crash, resulting in a denial of service.
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Description OSIDB Bzimport 2026-08-15 12:47:26 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net/smc: fix socket use-after-free during link group termination

__smc_lgr_terminate() drops conns_lock after finding a connection in
lgr->conns_all, but before taking a reference on its socket. The connection
is embedded in the socket, and its registration reference protects it only
while the connection remains in the tree.

A concurrent close can unregister the connection and drop that reference,
freeing the socket before the termination worker reaches sock_hold().

The race is reachable when close overlaps link group termination.
Local stress testing reproduced the use-after-free and KASAN reported:

  BUG: KASAN: slab-use-after-free in __smc_lgr_terminate.part.0 [smc]
  Write of size 4 by task kworker/3:3
  Workqueue: events smc_lgr_terminate_work [smc]
  __smc_lgr_terminate.part.0 [smc]

The socket was allocated by smc_create(), freed through
slab_free_after_rcu_debug(), and was followed by:

  refcount_t: addition on 0; use-after-free.
  __smc_lgr_terminate.part.0 [smc]

Take the socket reference while conns_lock still protects the tree entry.
The unregister path then cannot drop the last reference until termination
has finished using the socket.
Comment 1 Mauro Matteo Cascella 2026-08-19 16:56:23 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081539-CVE-2026-74493-cf51@gregkh/T