CIFS: Fix possible use after free in demultiplex thread

The recent changes that added SMB3 encryption support introduced
a possible use after free in the demultiplex thread. When we
process an encrypted packed we obtain a pointer to SMB session
but do not obtain a reference. This can possibly lead to a situation
when this session was freed before we copy a decryption key from
there. Fix this by obtaining a copy of the key rather than a pointer
to the session under a spinlock.

Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 26 insertions, 6 deletions

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index a44b4dbe4aae..d2cdd9c19d17 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1609,6 +1609,26 @@ static void cifs_crypt_complete(struct crypto_async_request *req, int err)
         complete(&res->completion);
 }
 
+static int
+smb2_get_enc_key(struct TCP_Server_Info *server, __u64 ses_id, int enc, u8 *key)
+{
+        struct cifs_ses *ses;
+        u8 *ses_enc_key;
+
+        spin_lock(&cifs_tcp_ses_lock);
+        list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
+                if (ses->Suid != ses_id)
+                        continue;
+                ses_enc_key = enc ? ses->smb3encryptionkey :
+                                                        ses->smb3decryptionkey;
+                memcpy(key, ses_enc_key, SMB3_SIGN_KEY_SIZE);
+                spin_unlock(&cifs_tcp_ses_lock);
+                return 0;
+        }
+        spin_unlock(&cifs_tcp_ses_lock);
+
+        return 1;
+}
 /*
  * Encrypt or decrypt @rqst message. @rqst has the following format:
  * iov[0] - transform header (associate data),
@@ -1622,10 +1642,10 @@ crypt_message(struct TCP_Server_Info *server, struct smb_rqst *rqst, int enc)
         struct smb2_transform_hdr *tr_hdr =
                         (struct smb2_transform_hdr *)rqst->rq_iov[0].iov_base;
         unsigned int assoc_data_len = sizeof(struct smb2_transform_hdr) - 24;
-        struct cifs_ses *ses;
         int rc = 0;
         struct scatterlist *sg;
         u8 sign[SMB2_SIGNATURE_SIZE] = {};
+        u8 key[SMB3_SIGN_KEY_SIZE];
         struct aead_request *req;
         char *iv;
         unsigned int iv_len;
@@ -1635,9 +1655,10 @@ crypt_message(struct TCP_Server_Info *server, struct smb_rqst *rqst, int enc)
 
         init_completion(&result.completion);
 
-        ses = smb2_find_smb_ses(server, tr_hdr->SessionId);
-        if (!ses) {
-                cifs_dbg(VFS, "%s: Could not find session\n", __func__);
+        rc = smb2_get_enc_key(server, tr_hdr->SessionId, enc, key);
+        if (rc) {
+                cifs_dbg(VFS, "%s: Could not get %scryption key\n", __func__,
+                         enc ? "en" : "de");
                 return 0;
         }
 
@@ -1649,8 +1670,7 @@ crypt_message(struct TCP_Server_Info *server, struct smb_rqst *rqst, int enc)
 
         tfm = enc ? server->secmech.ccmaesencrypt :
                                                 server->secmech.ccmaesdecrypt;
-        rc = crypto_aead_setkey(tfm, enc ? ses->smb3encryptionkey :
-                                ses->smb3decryptionkey, SMB3_SIGN_KEY_SIZE);
+        rc = crypto_aead_setkey(tfm, key, SMB3_SIGN_KEY_SIZE);
         if (rc) {
                 cifs_dbg(VFS, "%s: Failed to set aead key %d\n", __func__, rc);
                 return rc;