buffer overflows in the tty flip buffer in 2.6.17

buffer overflows in the tty flip buffer in 2.6.17

[Mockern]

When data is received from the hardware, it needs to be placed into the tty device's flip buffer. This can be done with the following bit of code:

for (i = 0; i < data_size; ++i) {
        if (tty->flip.count >= TTY_FLIPBUF_SIZE)
                tty_flip_buffer_push(tty);
        tty_insert_flip_char(tty, data[i], 0);
}
tty_flip_buffer_push(tty);

This example makes sure there are no buffer overflows in the tty flip buffer as the data is being added. 

But how it is done in 2.6.17 linux kernel? I did check this "overflow code" in new tty driver's code. This code looks like just removed. But somehow overflow in the tty buffer must be kept.

Re: buffer overflows in the tty flip buffer in 2.6.17

[Jiri Slaby]

Mockern napsal(a):
> When data is received from the hardware, it needs to be placed into the tty device's flip buffer. This can be done with the following bit of code:
> 

> for (i = 0; i < data_size; ++i) {
>         if (tty->flip.count >= TTY_FLIPBUF_SIZE)
>                 tty_flip_buffer_push(tty);
>         tty_insert_flip_char(tty, data[i], 0);
> }
> tty_flip_buffer_push(tty);

size = tty_buffer_request_room(tty, data_size);
tty_insert_flip_string(tty, data, min(data_size, size));
tty_flip_buffer_push(tty);
+ cope with size < data_size (some data_size -= size with 3 lines above in do {} 
while (data_size))

regards,
-- 
http://www.fi.muni.cz/~xslaby/            Jiri Slaby
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
B674 9967 0407 CE62 ACC8  22A0 32CC 55C3 39D4 7A7E

Hnus <hnus@fi.muni.cz> is an alias for /dev/null

Re: buffer overflows in the tty flip buffer in 2.6.17

[Lennart Sorensen]

On Sat, Feb 17, 2007 at 03:29:31PM +0300, Mockern wrote:
> When data is received from the hardware, it needs to be placed into the tty device's flip buffer. This can be done with the following bit of code:
> 
> for (i = 0; i < data_size; ++i) {
>         if (tty->flip.count >= TTY_FLIPBUF_SIZE)
>                 tty_flip_buffer_push(tty);
>         tty_insert_flip_char(tty, data[i], 0);
> }
> tty_flip_buffer_push(tty);
> 
> This example makes sure there are no buffer overflows in the tty flip buffer as the data is being added. 
> 
> But how it is done in 2.6.17 linux kernel? I did check this "overflow code" in new tty driver's code. This code looks like just removed. But somehow overflow in the tty buffer must be kept.

Well there was a problem in 2.6.16, which was fixed by 2.6.18, although
I am not sure if it was done by 2.6.17.  It would loose characters due
to buffer overflow and not properly checking under high load.  I grabbed
a few patches from the git tree that were added after 2.6.16 to fix the
tty problems I was having.

--
Len Sorensen

Re: buffer overflows in the tty flip buffer in 2.6.17

[Mockern]

Thanx for your respond. 

Could you please inform me what patches exactly you have grabbed?

>On Sat, Feb 17, 2007 at 03:29:31PM +0300, Mockern wrote:
>> When data is received from the hardware, it needs to be placed into the tty device's flip buffer. This can be done with the following bit of code:
>> 
>> for (i = 0; i < data_size; ++i) {
>>         if (tty->flip.count >= TTY_FLIPBUF_SIZE)
>>                 tty_flip_buffer_push(tty);
>>         tty_insert_flip_char(tty, data[i], 0);
>> }
>> tty_flip_buffer_push(tty);
>> 
>> This example makes sure there are no buffer overflows in the tty flip buffer as the data is being added. 
>> 
>> But how it is done in 2.6.17 linux kernel? I did check this "overflow code" in new tty driver's code. This code looks like just removed. But somehow overflow in the tty buffer must be kept.
>
>Well there was a problem in 2.6.16, which was fixed by 2.6.18, although
>I am not sure if it was done by 2.6.17.  It would loose characters due
>to buffer overflow and not properly checking under high load.  I grabbed
>a few patches from the git tree that were added after 2.6.16 to fix the
>tty problems I was having.
>
>--
>Len Sorensen
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-- 
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Re: buffer overflows in the tty flip buffer in 2.6.17

[Lennart Sorensen]

On Sat, Feb 17, 2007 at 06:52:03PM +0300, Mockern wrote:
> Thanx for your respond. 
> 
> Could you please inform me what patches exactly you have grabbed?

If you see the thread "Re: Strange problem with tty layer", which I just
posted a final update too, it has the list of linux-2.6 git commits that
I applied to 2.6.16 in order (some of them are probably in 2.6.17
already, while others might not be).

--
Len Sorensen

Re: buffer overflows in the tty flip buffer in 2.6.17

[Alan]

> But how it is done in 2.6.17 linux kernel? I did check this "overflow code" in new tty driver's code. This code looks like just removed. But somehow overflow in the tty buffer must be kept.

The new tty layer manages memory allocation dynamically and handles
overflows itself. Just throw data at it and the right thing will occur in
current kernels.