[alsa-devel] [PATCH] ALSA: firewire-lib: fix buffer-over-run when detecting packet discontinuity

[Takashi Iwai]

At Thu, 28 May 2015 00:02:59 +0900,
Takashi Sakamoto wrote:
> 
> When detecting packet discontinuity, handle_in_packet() returns minus value
> and this value is assigned to unsigned int variable, then the variable has
> huge value. As a result, the variable causes buffer-over-run in
> handle_out_packet(). This brings invalid page request and system hangup.
> 
> This commit fixes the bug to add a new argument into handle_in_packet()
> and the number of handled data blocks is assignd to it. The function
> return value is just used to check error.
> 
> I also considered to change the type of local variable to 'int' in
> in_stream_callback(). This idea is based on type-conversion in C standard,
> while it may cause future problems when adding more works. Thus, I dropped
> this idea.
> 
> Fixes: 6fc6b9ce41c6('ALSA: firewire-lib: pass the number of data blocks in incoming packets to outgoing packets')
> Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
> Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>

Applied, thanks.


Takashi

> ---
>  sound/firewire/amdtp.c | 32 ++++++++++++++++----------------
>  1 file changed, 16 insertions(+), 16 deletions(-)
> 
> diff --git a/sound/firewire/amdtp.c b/sound/firewire/amdtp.c
> index 2b3e8b1..7bb988f 100644
> --- a/sound/firewire/amdtp.c
> +++ b/sound/firewire/amdtp.c
> @@ -688,10 +688,10 @@ static int handle_out_packet(struct amdtp_stream *s, unsigned int data_blocks,
>  }
>  
>  static int handle_in_packet(struct amdtp_stream *s,
> -			    unsigned int payload_quadlets, __be32 *buffer)
> +			    unsigned int payload_quadlets, __be32 *buffer,
> +			    unsigned int *data_blocks)
>  {
>  	u32 cip_header[2];
> -	unsigned int data_blocks;
>  	unsigned int data_block_quadlets, data_block_counter, dbc_interval;
>  	struct snd_pcm_substream *pcm = NULL;
>  	bool lost;
> @@ -709,7 +709,7 @@ static int handle_in_packet(struct amdtp_stream *s,
>  		dev_info_ratelimited(&s->unit->device,
>  				"Invalid CIP header for AMDTP: %08X:%08X\n",
>  				cip_header[0], cip_header[1]);
> -		data_blocks = 0;
> +		*data_blocks = 0;
>  		goto end;
>  	}
>  
> @@ -717,7 +717,7 @@ static int handle_in_packet(struct amdtp_stream *s,
>  	if (payload_quadlets < 3 ||
>  	    ((cip_header[1] & CIP_FDF_MASK) ==
>  				(AMDTP_FDF_NO_DATA << CIP_FDF_SHIFT))) {
> -		data_blocks = 0;
> +		*data_blocks = 0;
>  	} else {
>  		data_block_quadlets =
>  			(cip_header[0] & CIP_DBS_MASK) >> CIP_DBS_SHIFT;
> @@ -731,12 +731,12 @@ static int handle_in_packet(struct amdtp_stream *s,
>  		if (s->flags & CIP_WRONG_DBS)
>  			data_block_quadlets = s->data_block_quadlets;
>  
> -		data_blocks = (payload_quadlets - 2) / data_block_quadlets;
> +		*data_blocks = (payload_quadlets - 2) / data_block_quadlets;
>  	}
>  
>  	/* Check data block counter continuity */
>  	data_block_counter = cip_header[0] & CIP_DBC_MASK;
> -	if (data_blocks == 0 && (s->flags & CIP_EMPTY_HAS_WRONG_DBC) &&
> +	if (*data_blocks == 0 && (s->flags & CIP_EMPTY_HAS_WRONG_DBC) &&
>  	    s->data_block_counter != UINT_MAX)
>  		data_block_counter = s->data_block_counter;
>  
> @@ -746,10 +746,10 @@ static int handle_in_packet(struct amdtp_stream *s,
>  	} else if (!(s->flags & CIP_DBC_IS_END_EVENT)) {
>  		lost = data_block_counter != s->data_block_counter;
>  	} else {
> -		if ((data_blocks > 0) && (s->tx_dbc_interval > 0))
> +		if ((*data_blocks > 0) && (s->tx_dbc_interval > 0))
>  			dbc_interval = s->tx_dbc_interval;
>  		else
> -			dbc_interval = data_blocks;
> +			dbc_interval = *data_blocks;
>  
>  		lost = data_block_counter !=
>  		       ((s->data_block_counter + dbc_interval) & 0xff);
> @@ -762,30 +762,30 @@ static int handle_in_packet(struct amdtp_stream *s,
>  		return -EIO;
>  	}
>  
> -	if (data_blocks > 0) {
> +	if (*data_blocks > 0) {
>  		buffer += 2;
>  
>  		pcm = ACCESS_ONCE(s->pcm);
>  		if (pcm)
> -			s->transfer_samples(s, pcm, buffer, data_blocks);
> +			s->transfer_samples(s, pcm, buffer, *data_blocks);
>  
>  		if (s->midi_ports)
> -			read_midi_messages(s, buffer, data_blocks);
> +			read_midi_messages(s, buffer, *data_blocks);
>  	}
>  
>  	if (s->flags & CIP_DBC_IS_END_EVENT)
>  		s->data_block_counter = data_block_counter;
>  	else
>  		s->data_block_counter =
> -				(data_block_counter + data_blocks) & 0xff;
> +				(data_block_counter + *data_blocks) & 0xff;
>  end:
>  	if (queue_in_packet(s) < 0)
>  		return -EIO;
>  
>  	if (pcm)
> -		update_pcm_pointers(s, pcm, data_blocks);
> +		update_pcm_pointers(s, pcm, *data_blocks);
>  
> -	return data_blocks;
> +	return 0;
>  }
>  
>  static void out_stream_callback(struct fw_iso_context *context, u32 cycle,
> @@ -853,8 +853,8 @@ static void in_stream_callback(struct fw_iso_context *context, u32 cycle,
>  			break;
>  		}
>  
> -		data_blocks = handle_in_packet(s, payload_quadlets, buffer);
> -		if (data_blocks < 0) {
> +		if (handle_in_packet(s, payload_quadlets, buffer,
> +							&data_blocks) < 0) {
>  			s->packet_index = -1;
>  			break;
>  		}
> -- 
> 2.1.4
>