Re: [PATCH] fix verify_command to allow burning more than 1 DVD

[Peter Osterlund <petero2@telia.com>]

Michal Schmidt <xschmi00@stud.feec.vutbr.cz> writes:

> I use K3B with growisofs to burn DVDs. After boot I can burn a DVD as
> a normal user. But only the first one. When I want to burn another
> one, K3B complains that it is unable to prevent media removal. Then
> only root can burn DVDs.
> The bug is in the kernel in the function verify_command.
> When a process opens the DVD recorder with O_RDONLY and issues a
> command which is marked safe_for_write, this function is supposed to
> just return -EPERM and do nothing more. However, there is a bug that
> causes the command to be marked as CMD_WARNED. From now on no
> non-privileged process is able to issue this command even if it
> correctly opens the device with O_RDWR - because the command is no
> longer marked as CMD_WRITE_SAFE.
> A patch is attached.
> 
> Michal
> --- linux-2.6.11-mm1/drivers/block/scsi_ioctl.c.orig	2005-01-17 20:42:40.000000000 +0100
> +++ linux-2.6.11-mm1/drivers/block/scsi_ioctl.c	2005-01-17 20:43:14.000000000 +0100
> @@ -197,9 +197,7 @@ static int verify_command(struct file *f
>  	if (type & CMD_WRITE_SAFE) {
>  		if (file->f_mode & FMODE_WRITE)
>  			return 0;
> -	}
> -
> -	if (!(type & CMD_WARNED)) {
> +	} else if (!(type & CMD_WARNED)) {
>  		cmd_type[cmd[0]] = CMD_WARNED;
>  		printk(KERN_WARNING "scsi: unknown opcode 0x%02x\n", cmd[0]);
>  	}

That patch will not write the warning message in some cases. I think
this patch is better:

---

 linux-petero/drivers/block/scsi_ioctl.c |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

diff -puN drivers/block/scsi_ioctl.c~scsi-filter drivers/block/scsi_ioctl.c
--- linux/drivers/block/scsi_ioctl.c~scsi-filter	2005-01-18 23:38:37.966026728 +0100
+++ linux-petero/drivers/block/scsi_ioctl.c	2005-01-18 23:38:37.970026120 +0100
@@ -200,7 +200,7 @@ static int verify_command(struct file *f
 	}
 
 	if (!(type & CMD_WARNED)) {
-		cmd_type[cmd[0]] = CMD_WARNED;
+		cmd_type[cmd[0]] |= CMD_WARNED;
 		printk(KERN_WARNING "scsi: unknown opcode 0x%02x\n", cmd[0]);
 	}
 
_

-- 
Peter Osterlund - petero2@telia.com
http://web.telia.com/~u89404340