Messages in this thread | | | Date | Fri, 13 Nov 2020 15:00:52 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH] lib: vsprintf: Avoid 32-bit truncation in vsscanf number parsing |
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On Thu 2020-11-12 12:04:27, Steven Rostedt wrote: > On Thu, 12 Nov 2020 15:46:46 +0000 > Richard Fitzgerald <rf@opensource.cirrus.com> wrote: > > > See this thread from 2014 where the field width problem was raised and > > explained: > > http://lkml.iu.edu/hypermail/linux/kernel/1401.1/03443.html > > > > and the reply from Linus Torvalds that was against fixing field width > > handling: > > http://lkml.iu.edu/hypermail/linux/kernel/1401.1/03488.html > > Thanks for the pointers, but note, that references to older emails should > use https://lore.kernel.org/ as these links format the output really > horribly. > > > > > which I assume is why the field handling wasn't unoptimized to be > > strictly correct.
Honestly, the handling of the number width by div does not look like a real optimization to me. It avoids the need of the temporary buffer by expensive and error-prone operation.
IMHO, it is safe to assume that the width will be limited so that the value would never overflow.
The longest supported number would be (2^64 - 1) in octal. If I am counting correctly, it is
01777777777777777777777
and it fits into buf[24] including the trailing '\0'.
We could call WARN_ON_ONCE() when the width >= 24 is higher. And we could add a compiler check when long long is bigger than 64-bit.
> Yes, but perhaps its time to fix the real problem and not just add > band-aids. That thread is over 6 years old (the email was from Jan 14, 2014) > > $ git diff `git rev-list --before 'Jan 14 2014' HEAD --max-count=1` | > grep '^+' | grep sscanf | wc -l > 622 > > There's been over 600 new additions of sscanf(). Now is the time to just > fix it correctly.
And the following one might suffer from this problem:
drivers/soundwire/slave.c: ret = sscanf(compat, "sdw%01x%04hx%04hx%02hhx", &sdw_version,
I agree with Steven that it is time to fix it properly.
Best Regards, Petr
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