Re: [PATCH] scsi: fix use-after-free in scsi_init_io()

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On Mon, 2010-08-16 at 16:15 +0200, Tejun Heo wrote:
> scsi_init_io() dereferences scsi_cmnd after putting it in the error
> path leading to oops.  Fix it.
> 
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxx
> ---
>  drivers/scsi/scsi_lib.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Index: block/drivers/scsi/scsi_lib.c
> ===================================================================
> --- block.orig/drivers/scsi/scsi_lib.c
> +++ block/drivers/scsi/scsi_lib.c
> @@ -968,7 +968,9 @@ static int scsi_init_sgtable(struct requ
>   */
>  int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
>  {
> +	struct request *req = cmd->request;
>  	int error = scsi_init_sgtable(cmd->request, &cmd->sdb, gfp_mask);
> +
>  	if (error)
>  		goto err_exit;
> 
> @@ -1012,7 +1014,7 @@ int scsi_init_io(struct scsi_cmnd *cmd,
>  err_exit:
>  	scsi_release_buffers(cmd);
>  	scsi_put_command(cmd);
> -	cmd->request->special = NULL;
> +	req->special = NULL;

Thanks for the bug report.  The fix is a bit heavy handed; what about
this?

James

---

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9ade720..ee02d38 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1011,8 +1011,8 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
 
 err_exit:
 	scsi_release_buffers(cmd);
-	scsi_put_command(cmd);
 	cmd->request->special = NULL;
+	scsi_put_command(cmd);
 	return error;
 }
 EXPORT_SYMBOL(scsi_init_io);


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