scsi: iscsi: target: Don't use stack buffer for scatterlist

Fedora got a bug report of a crash with iSCSI:

kernel BUG at include/linux/scatterlist.h:143!
...
RIP: 0010:iscsit_do_crypto_hash_buf+0x154/0x180 [iscsi_target_mod]
...
 Call Trace:
  ? iscsi_target_tx_thread+0x200/0x200 [iscsi_target_mod]
  iscsit_get_rx_pdu+0x4cd/0xa90 [iscsi_target_mod]
  ? native_sched_clock+0x3e/0xa0
  ? iscsi_target_tx_thread+0x200/0x200 [iscsi_target_mod]
  iscsi_target_rx_thread+0x81/0xf0 [iscsi_target_mod]
  kthread+0x120/0x140
  ? kthread_create_worker_on_cpu+0x70/0x70
  ret_from_fork+0x3a/0x50

This is a BUG_ON for using a stack buffer with a scatterlist.  There
are two cases that trigger this bug. Switch to using a dynamically
allocated buffer for one case and do not assign a NULL buffer in
another case.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index 9cdfccbdd06f..cc756a123fd8 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -1416,7 +1416,8 @@ static void iscsit_do_crypto_hash_buf(struct ahash_request *hash,
 
         sg_init_table(sg, ARRAY_SIZE(sg));
         sg_set_buf(sg, buf, payload_length);
-        sg_set_buf(sg + 1, pad_bytes, padding);
+        if (padding)
+                sg_set_buf(sg + 1, pad_bytes, padding);
 
         ahash_request_set_crypt(hash, sg, data_crc, payload_length + padding);
 
@@ -3910,10 +3911,14 @@ static bool iscsi_target_check_conn_state(struct iscsi_conn *conn)
 static void iscsit_get_rx_pdu(struct iscsi_conn *conn)
 {
         int ret;
-        u8 buffer[ISCSI_HDR_LEN], opcode;
+        u8 *buffer, opcode;
         u32 checksum = 0, digest = 0;
         struct kvec iov;
 
+        buffer = kcalloc(ISCSI_HDR_LEN, sizeof(*buffer), GFP_KERNEL);
+        if (!buffer)
+                return;
+
         while (!kthread_should_stop()) {
                 /*
                  * Ensure that both TX and RX per connection kthreads
@@ -3921,7 +3926,6 @@ static void iscsit_get_rx_pdu(struct iscsi_conn *conn)
                  */
                 iscsit_thread_check_cpumask(conn, current, 0);
 
-                memset(buffer, 0, ISCSI_HDR_LEN);
                 memset(&iov, 0, sizeof(struct kvec));
 
                 iov.iov_base    = buffer;
@@ -3930,7 +3934,7 @@ static void iscsit_get_rx_pdu(struct iscsi_conn *conn)
                 ret = rx_data(conn, &iov, 1, ISCSI_HDR_LEN);
                 if (ret != ISCSI_HDR_LEN) {
                         iscsit_rx_thread_wait_for_tcp(conn);
-                        return;
+                        break;
                 }
 
                 if (conn->conn_ops->HeaderDigest) {
@@ -3940,7 +3944,7 @@ static void iscsit_get_rx_pdu(struct iscsi_conn *conn)
                         ret = rx_data(conn, &iov, 1, ISCSI_CRC_LEN);
                         if (ret != ISCSI_CRC_LEN) {
                                 iscsit_rx_thread_wait_for_tcp(conn);
-                                return;
+                                break;
                         }
 
                         iscsit_do_crypto_hash_buf(conn->conn_rx_hash, buffer,
@@ -3964,7 +3968,7 @@ static void iscsit_get_rx_pdu(struct iscsi_conn *conn)
                 }
 
                 if (conn->conn_state == TARG_CONN_STATE_IN_LOGOUT)
-                        return;
+                        break;
 
                 opcode = buffer[0] & ISCSI_OPCODE_MASK;
 
@@ -3975,13 +3979,15 @@ static void iscsit_get_rx_pdu(struct iscsi_conn *conn)
                         " while in Discovery Session, rejecting.\n", opcode);
                         iscsit_add_reject(conn, ISCSI_REASON_PROTOCOL_ERROR,
                                           buffer);
-                        return;
+                        break;
                 }
 
                 ret = iscsi_target_rx_opcode(conn, buffer);
                 if (ret < 0)
-                        return;
+                        break;
         }
+
+        kfree(buffer);
 }
 
 int iscsi_target_rx_thread(void *arg)