Re: [PATCH net v7] net/smc: fix lgr/lnk lifetime vs diag reader race

[sashiko-bot@kernel.org]

> The diag dump walks the socket hash table under a read_lock and dereferences
> conn->lgr and conn->lnk. Three paths expose a window where a hashed socket has
> freed or partially freed conn/lgr/lnk state.
> 
> First, smc_conn_abort() calls smc_conn_free() during early handshake aborts
> while the socket is still hashed in SMC_INIT. On the smc_lgr_cleanup_early()
> path this frees the lgr synchronously without holding the hash write_lock. A
> concurrent diag reader can therefore load a non-NULL conn->lgr and dereference
> lgr->is_smcd after the kfree. Guard the conn->lgr->is_smcd load in
> __smc_diag_dump() by skipping it when the socket is in SMC_INIT state. The same
> guard also skips the CONNINFO/LGRINFO/DMBINFO blocks for SMC_CLOSED sockets,
> which may briefly remain hashed after smc_conn_free() when the fd is still open;
> smcss already suppresses those attributes for closed sockets, so there is no
> observability regression.
> 
> Second, in smc_conn_kill() on SMC-D with dmb_nocopy, smcd_buf_detach() NULLs and
> frees conn->sndbuf_desc before the socket is unhashed. A concurrent diag reader
> entering the CONNINFO block can dereference the freed descriptor. Unhash the
> socket at the top of smc_conn_kill(), before smcd_buf_detach().
> 
> Third, in the terminal teardown branches of smc_close_active_abort()
> (PEERCLOSEWAIT and PROCESSABORT groups) and in smc_close_passive_work(),
> smc_conn_free() drops lgr and lnk references while the socket is still hashed.
> Unhash immediately before each smc_conn_free() call at those two sites.
> 
> Fixes: f16a7dd5cf27 ("smc: netlink interface for SMC sockets")
> Fixes: 9dbe086c69b8 ("net/smc: fix invalid link access in dumping SMC-R connections")
> Fixes: ae2be35cbed2 ("net/smc: {at|de}tach sndbuf to peer DMB if supported")
> Cc: stable@vger.kernel.org
> Signed-off-by: Mahanta Jambigi <mjambigi@linux.ibm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260930073029.1201202-1-mjambigi@linux.ibm.com?part=1