smb: client: fix UAF in decryption with multichannel

After commit f7025d8 ("smb: client: allocate crypto only for
primary server") and commit b0abcd6 ("smb: client: fix UAF in
async decryption"), the channels started reusing AEAD TFM from primary
channel to perform synchronous decryption, but that can't done as
there could be multiple cifsd threads (one per channel) simultaneously
accessing it to perform decryption.

This fixes the following KASAN splat when running fstest generic/249
with 'vers=3.1.1,multichannel,max_channels=4,seal' against Windows
Server 2022:

BUG: KASAN: slab-use-after-free in gf128mul_4k_lle+0xba/0x110
Read of size 8 at addr ffff8881046c18a0 by task cifsd/986
CPU: 3 UID: 0 PID: 986 Comm: cifsd Not tainted 6.15.0-rc1 #1
PREEMPT(voluntary)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-3.fc41
04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x5d/0x80
 print_report+0x156/0x528
 ? gf128mul_4k_lle+0xba/0x110
 ? __virt_addr_valid+0x145/0x300
 ? __phys_addr+0x46/0x90
 ? gf128mul_4k_lle+0xba/0x110
 kasan_report+0xdf/0x1a0
 ? gf128mul_4k_lle+0xba/0x110
 gf128mul_4k_lle+0xba/0x110
 ghash_update+0x189/0x210
 shash_ahash_update+0x295/0x370
 ? __pfx_shash_ahash_update+0x10/0x10
 ? __pfx_shash_ahash_update+0x10/0x10
 ? __pfx_extract_iter_to_sg+0x10/0x10
 ? ___kmalloc_large_node+0x10e/0x180
 ? __asan_memset+0x23/0x50
 crypto_ahash_update+0x3c/0xc0
 gcm_hash_assoc_remain_continue+0x93/0xc0
 crypt_message+0xe09/0xec0 [cifs]
 ? __pfx_crypt_message+0x10/0x10 [cifs]
 ? _raw_spin_unlock+0x23/0x40
 ? __pfx_cifs_readv_from_socket+0x10/0x10 [cifs]
 decrypt_raw_data+0x229/0x380 [cifs]
 ? __pfx_decrypt_raw_data+0x10/0x10 [cifs]
 ? __pfx_cifs_read_iter_from_socket+0x10/0x10 [cifs]
 smb3_receive_transform+0x837/0xc80 [cifs]
 ? __pfx_smb3_receive_transform+0x10/0x10 [cifs]
 ? __pfx___might_resched+0x10/0x10
 ? __pfx_smb3_is_transform_hdr+0x10/0x10 [cifs]
 cifs_demultiplex_thread+0x692/0x1570 [cifs]
 ? __pfx_cifs_demultiplex_thread+0x10/0x10 [cifs]
 ? rcu_is_watching+0x20/0x50
 ? rcu_lockdep_current_cpu_online+0x62/0xb0
 ? find_held_lock+0x32/0x90
 ? kvm_sched_clock_read+0x11/0x20
 ? local_clock_noinstr+0xd/0xd0
 ? trace_irq_enable.constprop.0+0xa8/0xe0
 ? __pfx_cifs_demultiplex_thread+0x10/0x10 [cifs]
 kthread+0x1fe/0x380
 ? kthread+0x10f/0x380
 ? __pfx_kthread+0x10/0x10
 ? local_clock_noinstr+0xd/0xd0
 ? ret_from_fork+0x1b/0x60
 ? local_clock+0x15/0x30
 ? lock_release+0x29b/0x390
 ? rcu_is_watching+0x20/0x50
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x31/0x60
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>

Tested-by: David Howells <[email protected]>
Reported-by: Steve French <[email protected]>
Closes: https://lore.kernel.org/r/CAH2r5mu6Yc0-RJXM3kFyBYUB09XmXBrNodOiCVR4EDrmxq5Szg@mail.gmail.com
Fixes: f7025d8 ("smb: client: allocate crypto only for primary server")
Fixes: b0abcd6 ("smb: client: fix UAF in async decryption")
Signed-off-by: Paulo Alcantara (Red Hat) <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: pcacjr

fs/smb/client/cifsencrypt.c

@@ -704,18 +704,12 @@ cifs_crypto_secmech_release(struct TCP_Server_Info *server)
 	cifs_free_hash(&server->secmech.md5);
 	cifs_free_hash(&server->secmech.sha512);
 
-	if (!SERVER_IS_CHAN(server)) {
-		if (server->secmech.enc) {
-			crypto_free_aead(server->secmech.enc);
-			server->secmech.enc = NULL;
-		}
-
-		if (server->secmech.dec) {
-			crypto_free_aead(server->secmech.dec);
-			server->secmech.dec = NULL;
-		}
-	} else {
+	if (server->secmech.enc) {
+		crypto_free_aead(server->secmech.enc);
 		server->secmech.enc = NULL;
+	}
+	if (server->secmech.dec) {
+		crypto_free_aead(server->secmech.dec);
 		server->secmech.dec = NULL;
 	}
 }

fs/smb/client/smb2ops.c

@@ -4555,9 +4555,9 @@ decrypt_raw_data(struct TCP_Server_Info *server, char *buf,
 			return rc;
 		}
 	} else {
-		if (unlikely(!server->secmech.dec))
-			return -EIO;
-
+		rc = smb3_crypto_aead_allocate(server);
+		if (unlikely(rc))
+			return rc;
 		tfm = server->secmech.dec;
 	}
 

fs/smb/client/smb2pdu.c

@@ -1252,15 +1252,8 @@ SMB2_negotiate(const unsigned int xid,
 			cifs_server_dbg(VFS, "Missing expected negotiate contexts\n");
 	}
 
-	if (server->cipher_type && !rc) {
-		if (!SERVER_IS_CHAN(server)) {
-			rc = smb3_crypto_aead_allocate(server);
-		} else {
-			/* For channels, just reuse the primary server crypto secmech. */
-			server->secmech.enc = server->primary_server->secmech.enc;
-			server->secmech.dec = server->primary_server->secmech.dec;
-		}
-	}
+	if (server->cipher_type && !rc)
+		rc = smb3_crypto_aead_allocate(server);
 neg_exit:
 	free_rsp_buf(resp_buftype, rsp);
 	return rc;