Messages in this thread | | | Date | Thu, 6 Nov 2014 16:31:07 +0100 | From | Petr Mladek <> | Subject | Re: [RFC][PATCH 07/12 v3] tracing: Have seq_buf use full buffer |
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On Wed 2014-11-05 16:06:18, Steven Rostedt wrote: > On Wed, 5 Nov 2014 15:21:30 -0500 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > > > I wonder if we want this change at all. It means that we are not able to > > > detect overflow in some functions. It is pity because the users > > > might want to increase the buffer size and try again if the print > > > was incomplete. > > > > What do you mean we can't detect overflow? That's what > > seq_buf_has_overflowed() does. > > > > Although I'm looking at the seq_file versions of the bitmap code, which > does only return the len of what was written and not what would have > been written, and it does have this issue. > > I hate to go back to the -1 of the size of buffer as that causes > inconsistencies within the functions themselves, as proved with the > seq_file code.
Yeah, the -1 and the unused byte is strange and it would be great to avoid it.
On the other hand, I am slightly afraid of the "len = size + 1" that signalizes the buffer overflow. It might be prone for creating security bugs. If people forget to check seq_buf_has_overflowed() before reading or if there is a race, they might read outside of the buffer.
> What I might do as just have the bitmap calls not be allowed to fill > the buffer and keep the logic the same. That is, if the bitmap calls > fill the rest of the length, assume we overflowed, otherwise we are > fine. > > I'm going to change seq_buf to do that instead of my new update with > the bitmask code.
I like the idea of having the exception only in the bitmap code and filling the whole buffer in other cases.
I am now in doubts about the overflow state. A solution would be to add an "overflow" flag to struct seq_bug. I agree that it is ugly but it looks more secure then "len = size + 1".
Well, I do not have that strong opinion about it. What do you think?
Best Regards, Petr
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