Messages in this thread | | | From | David Laight <> | Subject | RE: Splicing to/from a tty | Date | Thu, 21 Jan 2021 10:08:30 +0000 |
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From: Linus Torvalds > Sent: 21 January 2021 01:04 > On Wed, Jan 20, 2021 at 4:38 PM Al Viro <viro@zeniv.linux.org.uk> wrote: > > > > OK... I wonder how many debugfs writable files allow pwrite() with > > BS results... > > I hope some of them check for "pos == 0" when they start parsing integers. > > But honestly, I don't think it's a big deal. We've had these things > that just basically assume that whenever you write, the offset just > doesn't matter at all, and as long as some number comes in one single > write call, we accept it. > > Because even if you end up doing something like just > > echo $SOMETHING > /sys/xyz/abc > > and that "$SOMETHING" could be done multiple writes, in practice it > all works out just fine and it never really is. You almost have to try > to screw up with something like > > (echo -n 3; echo -n 4) > /sys/xyz/abc > > to actually see two writes of "3" and "4" instead of one write with > "34". And honestly, if somebody does something like that, do we really > care? They might get 3, they might get 4, and they might get 34. They > get what they deserve.
Or worse: echo abc >/sys/xyz/abc echo x | dd bs=1 count=2 oseek=1 conv=notrunc of=/sys/xyz/abc which (if I got the dd command right) would generate "axc" on a real file.
OTOH multiple short reads are quite likely. Best not done on a counter...
David
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