scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()

Two latent bugs in the Text-phase handler, both present since the
original LIO integration in commit e48354ce07 ("iscsi-target: Add
iSCSI fabric support for target v4.1"):

1) DataDigest CRC buffer overread (4 bytes past text_in).

   text_in is kzalloc()'d at ALIGN(payload_length, 4).  rx_size is then
   incremented by ISCSI_CRC_LEN to make room for the received DataDigest
   in the iovec, but the same (now-bumped) rx_size is passed as the
   buffer length to iscsit_crc_buf():

       if (conn->conn_ops->DataDigest) {
               ...
               rx_size += ISCSI_CRC_LEN;
       }
       ...
       if (conn->conn_ops->DataDigest) {
               data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);

   iscsit_crc_buf() walks rx_size bytes of text_in with crc32c(), so
   when DataDigest is negotiated it reads 4 bytes past the end of the
   text_in allocation.  KASAN reproduces this directly on the unpatched
   mainline tree as slab-out-of-bounds in crc32c() called from the Text
   PDU path.  The OOB bytes feed crc32c() and are then compared against
   the initiator-supplied checksum, so the value does not flow back to
   the attacker, but the kernel does read past the buffer on every Text
   PDU with DataDigest=CRC32C.

   Fix by passing the actual padded payload length
   (ALIGN(payload_length, 4)) that was used for the kzalloc().

2) Stale cmd->text_in_ptr re-free (double-free) on ERL>0 bad DataDigest
   drop.

   On DataDigest mismatch with ErrorRecoveryLevel > 0 the handler
   silently drops the PDU and lets the initiator plug the CmdSN gap:

               kfree(text_in);
               return 0;

   cmd->text_in_ptr still points at the freed buffer.  The next Text
   Request on the same ITT re-enters iscsit_setup_text_cmd(), which
   unconditionally does

       kfree(cmd->text_in_ptr);
       cmd->text_in_ptr = NULL;

   freeing the same pointer a second time.  Session teardown via
   iscsit_release_cmd() has the same shape and hits the same double-free
   if the connection is dropped before a second Text Request arrives.

   On an unmodified mainline tree the bug-1 CRC overread fires first on
   the initial valid Text Request and perturbs the subsequent state, so
   #4 was isolated by building a kernel with only the bug-1 hunk of this
   patch applied plus temporary printk() observability around the three
   relevant kfree() sites.  The observability prints are not part of
   this patch.  On that build, a three-PDU Text Request sequence after
   login produces two back-to-back splats:

       BUG: KASAN: double-free in iscsit_setup_text_cmd+0x??
       BUG: KASAN: double-free in iscsit_release_cmd+0x??

   showing the same pointer freed in the ERL>0 drop path and again in
   iscsit_setup_text_cmd() (next Text Request on the same ITT) and once
   more in iscsit_release_cmd() (session teardown).  On distro kernels
   with CONFIG_SLAB_FREELIST_HARDENED=y (default) the double-free
   becomes a remote kernel BUG(); on non-hardened kernels it corrupts
   the slab freelist.

   Fix by clearing cmd->text_in_ptr after the kfree() in the ERL>0 drop
   path.  With both hunks applied #4 is directly observable on the stock
   tree without observability printks; fixing bug-1 alone would mask #4
   less, not more, so the hunks are submitted together.

Both fixes are one-liners.  The Text PDU state machine is unchanged and
the wire protocol is unaffected.

Fixes: e48354ce07 ("iscsi-target: Add iSCSI fabric support for target v4.1")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Tested-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/iscsi/iscsi_target.c

@@ -2295,7 +2295,9 @@ iscsit_handle_text_cmd(struct iscsit_conn *conn, struct iscsit_cmd *cmd,
 			goto reject;
 
 		if (conn->conn_ops->DataDigest) {
-			data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);
+			data_crc = iscsit_crc_buf(text_in,
+						  ALIGN(payload_length, 4),
+						  0, NULL);
 			if (checksum != data_crc) {
 				pr_err("Text data CRC32C DataDigest"
 					" 0x%08x does not match computed"
@@ -2314,6 +2316,7 @@ iscsit_handle_text_cmd(struct iscsit_conn *conn, struct iscsit_cmd *cmd,
 					" Command CmdSN: 0x%08x due to"
 					" DataCRC error.\n", hdr->cmdsn);
 					kfree(text_in);
+					cmd->text_in_ptr = NULL;
 					return 0;
 				}
 			} else {