Messages in this thread | | | Date | Sun, 19 May 2002 21:57:53 +0200 (CEST) | From | Roman Zippel <> | Subject | Re: AUDIT: copy_from_user is a deathtrap. |
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Hi,
On Sun, 19 May 2002, Linus Torvalds wrote:
> A faulting write will fill some subsequent memory area with zeroes, but a > subsequent write can complete the original one. > > It has to _commit_ the whole area, because it uses the pre-fault size > information to optimize away reads etc, ie if you do a > > write(fd, buf, 4096); > > at a page-aligned offset, the write code knows that it shouldn't read the > old contents because they get overwritten. > > Which is why we need to commit the whole 4096 bytes, even if we only > actually were able to get a single byte from user space.
I basically agree, but I think there is a special case: writing at the end of the file. Instead of writing zeros, we have to truncate the file, otherwise you can't restart append writes. Currently we get this wrong.
bye, Roman
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