Re: [PATCH v3] sound/oss: remove offset from load_patch callbacks

[Takashi Iwai <tiwai@suse.de>]

At Wed, 23 Mar 2011 10:53:41 -0400,
Dan Rosenberg wrote:
> 
> Was: [PATCH] sound/oss/midi_synth: prevent underflow, use of
> uninitialized value, and signedness issue
> 
> The offset passed to midi_synth_load_patch() can be essentially
> arbitrary.  If it's greater than the header length, this will result in
> a copy_from_user(dst, src, negative_val).  While this will just return
> -EFAULT on x86, on other architectures this may cause memory corruption.
> Additionally, the length field of the sysex_info structure may not be
> initialized prior to its use.  Finally, a signed comparison may result
> in an unintentionally large loop.
> 
> On suggestion by Takashi Iwai, version two removes the offset argument
> from the load_patch callbacks entirely, which also resolves similar
> issues in opl3.  Compile tested only.
> 
> v3 adjusts comments and hopefully gets copy offsets right.
> 
> Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>

Applied now.  Thanks.


Takashi

> ---
>  sound/oss/dev_table.h  |    2 +-
>  sound/oss/midi_synth.c |   30 +++++++++++++-----------------
>  sound/oss/midi_synth.h |    2 +-
>  sound/oss/opl3.c       |    8 ++------
>  sound/oss/sequencer.c  |    2 +-
>  5 files changed, 18 insertions(+), 26 deletions(-)
> 
> diff --git a/sound/oss/dev_table.h b/sound/oss/dev_table.h
> index b7617be..0199a31 100644
> --- a/sound/oss/dev_table.h
> +++ b/sound/oss/dev_table.h
> @@ -271,7 +271,7 @@ struct synth_operations
>  	void (*reset) (int dev);
>  	void (*hw_control) (int dev, unsigned char *event);
>  	int (*load_patch) (int dev, int format, const char __user *addr,
> -	     int offs, int count, int pmgr_flag);
> +	     int count, int pmgr_flag);
>  	void (*aftertouch) (int dev, int voice, int pressure);
>  	void (*controller) (int dev, int voice, int ctrl_num, int value);
>  	void (*panning) (int dev, int voice, int value);
> diff --git a/sound/oss/midi_synth.c b/sound/oss/midi_synth.c
> index 3c09374..2292c23 100644
> --- a/sound/oss/midi_synth.c
> +++ b/sound/oss/midi_synth.c
> @@ -476,7 +476,7 @@ EXPORT_SYMBOL(midi_synth_hw_control);
>  
>  int
>  midi_synth_load_patch(int dev, int format, const char __user *addr,
> -		      int offs, int count, int pmgr_flag)
> +		      int count, int pmgr_flag)
>  {
>  	int             orig_dev = synth_devs[dev]->midi_dev;
>  
> @@ -491,33 +491,29 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,
>  	if (!prefix_cmd(orig_dev, 0xf0))
>  		return 0;
>  
> +	/* Invalid patch format */
>  	if (format != SYSEX_PATCH)
> -	{
> -/*		  printk("MIDI Error: Invalid patch format (key) 0x%x\n", format);*/
>  		  return -EINVAL;
> -	}
> +
> +	/* Patch header too short */
>  	if (count < hdr_size)
> -	{
> -/*		printk("MIDI Error: Patch header too short\n");*/
>  		return -EINVAL;
> -	}
> +
>  	count -= hdr_size;
>  
>  	/*
> -	 * Copy the header from user space but ignore the first bytes which have
> -	 * been transferred already.
> +	 * Copy the header from user space
>  	 */
>  
> -	if(copy_from_user(&((char *) &sysex)[offs], &(addr)[offs], hdr_size - offs))
> +	if (copy_from_user(&sysex, addr, hdr_size))
>  		return -EFAULT;
> - 
> - 	if (count < sysex.len)
> -	{
> -/*		printk(KERN_WARNING "MIDI Warning: Sysex record too short (%d<%d)\n", count, (int) sysex.len);*/
> +
> +	/* Sysex record too short */
> +	if ((unsigned)count < (unsigned)sysex.len)
>  		sysex.len = count;
> -	}
> -  	left = sysex.len;
> -  	src_offs = 0;
> +
> +	left = sysex.len;
> +	src_offs = 0;
>  
>  	for (i = 0; i < left && !signal_pending(current); i++)
>  	{
> diff --git a/sound/oss/midi_synth.h b/sound/oss/midi_synth.h
> index 6bc9d00..b64ddd6 100644
> --- a/sound/oss/midi_synth.h
> +++ b/sound/oss/midi_synth.h
> @@ -8,7 +8,7 @@ int midi_synth_open (int dev, int mode);
>  void midi_synth_close (int dev);
>  void midi_synth_hw_control (int dev, unsigned char *event);
>  int midi_synth_load_patch (int dev, int format, const char __user * addr,
> -		 int offs, int count, int pmgr_flag);
> +		 int count, int pmgr_flag);
>  void midi_synth_panning (int dev, int channel, int pressure);
>  void midi_synth_aftertouch (int dev, int channel, int pressure);
>  void midi_synth_controller (int dev, int channel, int ctrl_num, int value);
> diff --git a/sound/oss/opl3.c b/sound/oss/opl3.c
> index 938c48c..cbf9574 100644
> --- a/sound/oss/opl3.c
> +++ b/sound/oss/opl3.c
> @@ -820,7 +820,7 @@ static void opl3_hw_control(int dev, unsigned char *event)
>  }
>  
>  static int opl3_load_patch(int dev, int format, const char __user *addr,
> -		int offs, int count, int pmgr_flag)
> +		int count, int pmgr_flag)
>  {
>  	struct sbi_instrument ins;
>  
> @@ -830,11 +830,7 @@ static int opl3_load_patch(int dev, int format, const char __user *addr,
>  		return -EINVAL;
>  	}
>  
> -	/*
> -	 * What the fuck is going on here?  We leave junk in the beginning
> -	 * of ins and then check the field pretty close to that beginning?
> -	 */
> -	if(copy_from_user(&((char *) &ins)[offs], addr + offs, sizeof(ins) - offs))
> +	if (copy_from_user(&ins, addr, sizeof(ins)))
>  		return -EFAULT;
>  
>  	if (ins.channel < 0 || ins.channel >= SBFM_MAXINSTR)
> diff --git a/sound/oss/sequencer.c b/sound/oss/sequencer.c
> index 5ea1098..30bcfe4 100644
> --- a/sound/oss/sequencer.c
> +++ b/sound/oss/sequencer.c
> @@ -241,7 +241,7 @@ int sequencer_write(int dev, struct file *file, const char __user *buf, int coun
>  				return -ENXIO;
>  
>  			fmt = (*(short *) &event_rec[0]) & 0xffff;
> -			err = synth_devs[dev]->load_patch(dev, fmt, buf, p + 4, c, 0);
> +			err = synth_devs[dev]->load_patch(dev, fmt, buf + p, c, 0);
>  			if (err < 0)
>  				return err;
>  
> 
>