linux-kernel - Re: [PATCH] Fix sg_io

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Date:	Wed, 31 Dec 2008 18:08:02 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	akpm@...ux-foundation.org
Cc:	alexey.zaytsev@...il.com, jens.axboe@...cle.com,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	James.Bottomley@...senPartnership.com
Subject: Re: [PATCH] Fix sg_io_hdr.info corruption.

On Tue, 30 Dec 2008 15:46:03 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Sun, 28 Dec 2008 17:50:35 +0300
> Alexey Zaytsev <alexey.zaytsev@...il.com> wrote:
> 
> > sizeof(unsigned (short)) is actually sizeof(function), == 1.
> > Spotted by sparse.
> > 
> > Signed-off-by: Alexey Zaytsev <alexey.zaytsev@...il.com>
> > ---
> >  fs/compat_ioctl.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
> > index 5235c67..7c2d617 100644
> > --- a/fs/compat_ioctl.c
> > +++ b/fs/compat_ioctl.c
> > @@ -784,7 +784,7 @@ static int sg_ioctl_trans(unsigned int fd, unsigned int cmd, unsigned long arg)
> >  
> >  	if (copy_in_user(&sgio->status, &sgio32->status,
> >  			 (4 * sizeof(unsigned char)) +
> > -			 (2 * sizeof(unsigned (short))) +
> > +			 (2 * sizeof(unsigned short)) +
> >  			 (3 * sizeof(int))))
> >  		return -EFAULT;
> 
> gack.
> 
> akpm:/home/akpm> cat t.c
> main()
> {
> 	        printf("%d\n", sizeof(unsigned (short)));
> 	        printf("%d\n", sizeof(unsigned short));
> }
> akpm:/home/akpm> ./a.out
> 1
> 2
> 
> 
> the code has been like this for years and years.  Why hasn't anyone
> noticed?  

The members from 'status' in struct sg_io_hdr to the last are used to
transfer information from kernel to user space. The values that user
space sets are just ignored.

typedef struct sg_io_hdr
{
    int interface_id;           /* [i] 'S' for SCSI generic (required) */
    int dxfer_direction;        /* [i] data transfer direction  */
    unsigned char cmd_len;      /* [i] SCSI command length ( <= 16 bytes) */
    unsigned char mx_sb_len;    /* [i] max length to write to sbp */
    unsigned short iovec_count; /* [i] 0 implies no scatter gather */
    unsigned int dxfer_len;     /* [i] byte count of data transfer */
    void __user *dxferp;	/* [i], [*io] points to data transfer memory
					      or scatter gather list */
    unsigned char __user *cmdp; /* [i], [*i] points to command to perform */
    void __user *sbp;		/* [i], [*o] points to sense_buffer memory */
    unsigned int timeout;       /* [i] MAX_UINT->no timeout (unit: millisec) */
    unsigned int flags;         /* [i] 0 -> default, see SG_FLAG... */
    int pack_id;                /* [i->o] unused internally (normally) */
    void __user * usr_ptr;      /* [i->o] unused internally */
    unsigned char status;       /* [o] scsi status */
    unsigned char masked_status;/* [o] shifted, masked scsi status */
    unsigned char msg_status;   /* [o] messaging level data (optional) */
    unsigned char sb_len_wr;    /* [o] byte count actually written to sbp */
    unsigned short host_status; /* [o] errors from host adapter */
    unsigned short driver_status;/* [o] errors from software driver */
    int resid;                  /* [o] dxfer_len - actual_transferred */
    unsigned int duration;      /* [o] time taken by cmd (unit: millisec) */
    unsigned int info;          /* [o] auxiliary information */
} sg_io_hdr_t;  /* 64 bytes long (on i386) */
--
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