[PATCH net] tipc: fix slab-use-after-free Read in tipc_aead_decrypt_done

[Doruk Tan Ozturk <doruk@0sec.ai>]

The async decrypt completion path mirrors the encrypt one but is missing
the net reference that guards against the tipc_crypto being freed during
netns teardown.

When crypto_aead_decrypt() is offloaded to cryptd (the SIMD aead wrapper
queues the request when crypto_simd_usable() is false), the cryptd worker
runs tipc_aead_decrypt_done() asynchronously. If the bearer's netns is
torn down in the meantime, tipc_exit_net() -> tipc_crypto_stop() frees the
tipc_crypto, and the completion then reads it: tipc_aead_decrypt_done()
dereferences aead->crypto->stats and aead->crypto->net, and
tipc_crypto_rcv_complete() dereferences aead->crypto->aead[] and the node
table, reading freed memory:

  BUG: KASAN: slab-use-after-free in tipc_crypto_rcv_complete
  Read of size 8 at addr ffff888104c8c808 by task kworker/3:2/70
  Workqueue: cryptd cryptd_queue_worker
  Call Trace:
   tipc_crypto_rcv_complete+0x1dd6/0x2240
   tipc_aead_decrypt_done+0x1c3/0x300
   cryptd_aead_crypt+0x3ae/0x660
   cryptd_queue_worker+0x12b/0x200
   process_one_work+0x66c/0x10c0
   worker_thread+0x55d/0xc80
   kthread+0x269/0x340
  Allocated by task 1550:
   tipc_crypto_start+0x7e/0x890
   tipc_init_net+0x30d/0x480
   ...
  Freed by task 116:
   tipc_crypto_stop+0x1a4/0x2a0
   tipc_exit_net+0x11c/0x1c0
   cleanup_net+0x510/0xaf0

This is the same class of bug that commit e279024617134 ("net/tipc: fix
slab-use-after-free Read in tipc_aead_encrypt_done") fixed for the
encrypt side. The encrypt path takes maybe_get_net(aead->crypto->net)
before crypto_aead_encrypt() and drops it with put_net() on the
synchronous return paths and in tipc_aead_encrypt_done(); the -EINPROGRESS
/-EBUSY return keeps the reference for the async callback to release. The
decrypt path was left without the equivalent guard.

Mirror the encrypt-side fix on the decrypt path: take a net reference
before crypto_aead_decrypt() (failing with -ENODEV and the matching
bearer put if it cannot be acquired), keep it across the -EINPROGRESS/
-EBUSY async return, and drop it with put_net() on the synchronous
success/error return and at the end of tipc_aead_decrypt_done().

Reproduced under KASAN on v6.12.92: a UDP bearer with a cluster key is
flooded with encrypted frames from an unknown peer (driving the cluster-
key decrypt path) while the bearer's netns is repeatedly torn down. The
SIMD aead must be forced onto its cryptd async child for the completion
to outlive tipc_crypto_stop(), and the cryptd worker was delayed to land
the narrow race deterministically; with the patch applied the same
workload runs cleanly. Found by 0sec automated security-research tooling
while auditing the siblings of commit e279024617134.

Found by 0sec automated security-research tooling (https://0sec.ai).

Fixes: fc1b6d6de220 ("tipc: introduce TIPC encryption & authentication")
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
---
 net/tipc/crypto.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/tipc/crypto.c b/net/tipc/crypto.c
index 6d3b6b89b1d1..84a6489da036 100644
--- a/net/tipc/crypto.c
+++ b/net/tipc/crypto.c
@@ -941,12 +941,20 @@ static int tipc_aead_decrypt(struct net *net, struct tipc_aead *aead,
 		goto exit;
 	}
 
+	/* Get net to avoid freed tipc_crypto when delete namespace */
+	if (!maybe_get_net(aead->crypto->net)) {
+		tipc_bearer_put(b);
+		rc = -ENODEV;
+		goto exit;
+	}
+
 	/* Now, do decrypt */
 	rc = crypto_aead_decrypt(req);
 	if (rc == -EINPROGRESS || rc == -EBUSY)
 		return rc;
 
 	tipc_bearer_put(b);
+	put_net(aead->crypto->net);
 
 exit:
 	kfree(ctx);
@@ -984,6 +992,7 @@ static void tipc_aead_decrypt_done(void *data, int err)
 	}
 
 	tipc_bearer_put(b);
+	put_net(net);
 }
 
 static inline int tipc_ehdr_size(struct tipc_ehdr *ehdr)
-- 
2.43.0