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[8/8] xen/hvc: replace BUG_ON() with negative return value

Message ID 20210513100302.22027-9-jgross@suse.com
State New
Headers show
Series xen: harden frontends against malicious backends | expand

Commit Message

Juergen Gross May 13, 2021, 10:03 a.m. UTC
Xen frontends shouldn't BUG() in case of illegal data received from
their backends. So replace the BUG_ON()s when reading illegal data from
the ring page with negative return values.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 drivers/tty/hvc/hvc_xen.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

Comments

Christophe Leroy May 13, 2021, 10:16 a.m. UTC | #1
Le 13/05/2021 à 12:03, Juergen Gross a écrit :
> Xen frontends shouldn't BUG() in case of illegal data received from
> their backends. So replace the BUG_ON()s when reading illegal data from
> the ring page with negative return values.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>   drivers/tty/hvc/hvc_xen.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
> index 92c9a476defc..30d7ffb1e04c 100644
> --- a/drivers/tty/hvc/hvc_xen.c
> +++ b/drivers/tty/hvc/hvc_xen.c
> @@ -86,6 +86,11 @@ static int __write_console(struct xencons_info *xencons,
>   	cons = intf->out_cons;
>   	prod = intf->out_prod;
>   	mb();			/* update queue values before going on */
> +
> +	if (WARN_ONCE((prod - cons) > sizeof(intf->out),
> +		      "Illegal ring page indices"))
> +		return -EINVAL;
> +
>   	BUG_ON((prod - cons) > sizeof(intf->out));

Why keep the BUG_ON() ?


>   
>   	while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
> @@ -114,7 +119,10 @@ static int domU_write_console(uint32_t vtermno, const char *data, int len)
>   	 */
>   	while (len) {
>   		int sent = __write_console(cons, data, len);
> -		
> +
> +		if (sent < 0)
> +			return sent;
> +
>   		data += sent;
>   		len -= sent;
>   
> @@ -138,7 +146,10 @@ static int domU_read_console(uint32_t vtermno, char *buf, int len)
>   	cons = intf->in_cons;
>   	prod = intf->in_prod;
>   	mb();			/* get pointers before reading ring */
> -	BUG_ON((prod - cons) > sizeof(intf->in));
> +
> +	if (WARN_ONCE((prod - cons) > sizeof(intf->in),
> +		      "Illegal ring page indices"))
> +		return -EINVAL;
>   
>   	while (cons != prod && recv < len)
>   		buf[recv++] = intf->in[MASK_XENCONS_IDX(cons++, intf->in)];
>
Juergen Gross May 13, 2021, 10:20 a.m. UTC | #2
On 13.05.21 12:16, Christophe Leroy wrote:
> 
> 
> Le 13/05/2021 à 12:03, Juergen Gross a écrit :
>> Xen frontends shouldn't BUG() in case of illegal data received from
>> their backends. So replace the BUG_ON()s when reading illegal data from
>> the ring page with negative return values.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>>   drivers/tty/hvc/hvc_xen.c | 15 +++++++++++++--
>>   1 file changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
>> index 92c9a476defc..30d7ffb1e04c 100644
>> --- a/drivers/tty/hvc/hvc_xen.c
>> +++ b/drivers/tty/hvc/hvc_xen.c
>> @@ -86,6 +86,11 @@ static int __write_console(struct xencons_info 
>> *xencons,
>>       cons = intf->out_cons;
>>       prod = intf->out_prod;
>>       mb();            /* update queue values before going on */
>> +
>> +    if (WARN_ONCE((prod - cons) > sizeof(intf->out),
>> +              "Illegal ring page indices"))
>> +        return -EINVAL;
>> +
>>       BUG_ON((prod - cons) > sizeof(intf->out));
> 
> Why keep the BUG_ON() ?

Oh, failed to delete it. Thanks for noticing.


Juergen
Greg KH May 13, 2021, 10:25 a.m. UTC | #3
On Thu, May 13, 2021 at 12:03:02PM +0200, Juergen Gross wrote:
> Xen frontends shouldn't BUG() in case of illegal data received from
> their backends. So replace the BUG_ON()s when reading illegal data from
> the ring page with negative return values.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  drivers/tty/hvc/hvc_xen.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
> index 92c9a476defc..30d7ffb1e04c 100644
> --- a/drivers/tty/hvc/hvc_xen.c
> +++ b/drivers/tty/hvc/hvc_xen.c
> @@ -86,6 +86,11 @@ static int __write_console(struct xencons_info *xencons,
>  	cons = intf->out_cons;
>  	prod = intf->out_prod;
>  	mb();			/* update queue values before going on */
> +
> +	if (WARN_ONCE((prod - cons) > sizeof(intf->out),
> +		      "Illegal ring page indices"))
> +		return -EINVAL;

How nice, you just rebooted on panic-on-warn systems :(

> +
>  	BUG_ON((prod - cons) > sizeof(intf->out));

Why keep this line?

Please just fix this up properly, if userspace can trigger this, then
both the WARN_ON() and BUG_ON() are not correct and need to be correctly
handled.


>  
>  	while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
> @@ -114,7 +119,10 @@ static int domU_write_console(uint32_t vtermno, const char *data, int len)
>  	 */
>  	while (len) {
>  		int sent = __write_console(cons, data, len);
> -		
> +
> +		if (sent < 0)
> +			return sent;
> +
>  		data += sent;
>  		len -= sent;
>  
> @@ -138,7 +146,10 @@ static int domU_read_console(uint32_t vtermno, char *buf, int len)
>  	cons = intf->in_cons;
>  	prod = intf->in_prod;
>  	mb();			/* get pointers before reading ring */
> -	BUG_ON((prod - cons) > sizeof(intf->in));
> +
> +	if (WARN_ONCE((prod - cons) > sizeof(intf->in),
> +		      "Illegal ring page indices"))
> +		return -EINVAL;

Same here, you still just paniced a machine :(

thanks,

greg k-h
Juergen Gross May 13, 2021, 10:35 a.m. UTC | #4
On 13.05.21 12:25, Greg Kroah-Hartman wrote:
> On Thu, May 13, 2021 at 12:03:02PM +0200, Juergen Gross wrote:
>> Xen frontends shouldn't BUG() in case of illegal data received from
>> their backends. So replace the BUG_ON()s when reading illegal data from
>> the ring page with negative return values.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>>   drivers/tty/hvc/hvc_xen.c | 15 +++++++++++++--
>>   1 file changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
>> index 92c9a476defc..30d7ffb1e04c 100644
>> --- a/drivers/tty/hvc/hvc_xen.c
>> +++ b/drivers/tty/hvc/hvc_xen.c
>> @@ -86,6 +86,11 @@ static int __write_console(struct xencons_info *xencons,
>>   	cons = intf->out_cons;
>>   	prod = intf->out_prod;
>>   	mb();			/* update queue values before going on */
>> +
>> +	if (WARN_ONCE((prod - cons) > sizeof(intf->out),
>> +		      "Illegal ring page indices"))
>> +		return -EINVAL;
> 
> How nice, you just rebooted on panic-on-warn systems :(
> 
>> +
>>   	BUG_ON((prod - cons) > sizeof(intf->out));
> 
> Why keep this line?

Failed to delete it, sorry.

> 
> Please just fix this up properly, if userspace can trigger this, then
> both the WARN_ON() and BUG_ON() are not correct and need to be correctly
> handled.

It can be triggered by the console backend, but I agree a WARN isn't the
way to go here.


Juergen
diff mbox series

Patch

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index 92c9a476defc..30d7ffb1e04c 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -86,6 +86,11 @@  static int __write_console(struct xencons_info *xencons,
 	cons = intf->out_cons;
 	prod = intf->out_prod;
 	mb();			/* update queue values before going on */
+
+	if (WARN_ONCE((prod - cons) > sizeof(intf->out),
+		      "Illegal ring page indices"))
+		return -EINVAL;
+
 	BUG_ON((prod - cons) > sizeof(intf->out));
 
 	while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
@@ -114,7 +119,10 @@  static int domU_write_console(uint32_t vtermno, const char *data, int len)
 	 */
 	while (len) {
 		int sent = __write_console(cons, data, len);
-		
+
+		if (sent < 0)
+			return sent;
+
 		data += sent;
 		len -= sent;
 
@@ -138,7 +146,10 @@  static int domU_read_console(uint32_t vtermno, char *buf, int len)
 	cons = intf->in_cons;
 	prod = intf->in_prod;
 	mb();			/* get pointers before reading ring */
-	BUG_ON((prod - cons) > sizeof(intf->in));
+
+	if (WARN_ONCE((prod - cons) > sizeof(intf->in),
+		      "Illegal ring page indices"))
+		return -EINVAL;
 
 	while (cons != prod && recv < len)
 		buf[recv++] = intf->in[MASK_XENCONS_IDX(cons++, intf->in)];