CVE-2026-98173smb: client: fix use-after-free of iface in cifs_try_adding_channels()

Official description

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix use-after-free of iface in cifs_try_adding_channels() cifs_try_adding_channels() iterates ses->iface_list with list_for_each_entry_safe_from(), which captures the next entry (niface) under iface_lock. The loop body then drops iface_lock for the whole duration of cifs_ses_add_channel(). A concurrent interface refresh (SMB3_request_interfaces() -> parse_server_interfaces()) marks all ifaces inactive and removes and frees any that are not re-advertised via list_del() + kref_put(), where release_iface() is a bare kfree(). Since niface typically has no channel holding a reference, the list reference is its last and it can be freed inside the unlocked window. On continue, the iterator advance step then dereferences niface->iface_head.next, and the loop body reads iface->rdma_capable/is_active, both on freed memory. Fix this by never keeping an unreferenced list pointer across the unlocked window. Each channel attempt now re-scans the list from the head under iface_lock, takes a kref on the selected candidate, and passes only that referenced candidate to cifs_ses_add_channel(). weight_fulfilled still tracks selection progress, so restarting the scan preserves the original weighted distribution and the weight_fulfilled-before-kref_put ordering on the failure path. Add a per-pass attempts cap so a flapping interface refresh cannot keep the inner loop spinning within a single tries increment.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/93e8a49adb2a575202c5ee766435eff2f9f95f5b
• https://git.kernel.org/stable/c/ee0d8f83d68f6e6509f092c997ccab3c8c801538
• https://git.kernel.org/stable/c/c941f1ebfd26f683de81091473f3596a218abff0
• https://git.kernel.org/stable/c/e99040e5e9c60441e6b4725e1a7b88c3106ae903
• https://git.kernel.org/stable/c/ec36b38e65596950e6c29bed7dfc90b98707c19c
• https://git.kernel.org/stable/c/d034e836eefd7ce75e588f7031cffbeec594f5ac