Messages in this thread | | | Date | Fri, 31 Aug 2007 19:48:12 -0600 | From | Robert Hancock <> | Subject | Re: Copy large memory regions from & to userspace |
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Clemens Kolbitsch wrote: > On Friday 31 August 2007 15:25:40 you wrote: >> On 8/30/07, Clemens Kolbitsch <clemens.kol@gmx.at> wrote: >>> Hi! >>> Just a short question: What is the correct method of copying large areas >>> of memory from userspace into userspace when running in kernel-mode? >> relayfs? > > no... I'm copying user-memory to user-memory, not kernel-to-user, however > running the code in kernel-mode. > > what i wanted to know is how to check the access-rights... > i didn't get any other answers, so for now i'm just using > > if (access_ok(VERIFY_READ, from, PAGE_SIZE) && > access_ok(VERIFY_WRITE, to, PAGE_SIZE)) > { > memcpy(to, from, PAGE_SIZE); > } > > and hope that this is the *correct* way to do it...
No, it's not. access_ok does not guarantee that the memory region can be validly read or written. It only allows using __copy_to_user or __copy_from_user which skips the same checks that access_ok does.
I'm not aware of any code in the kernel that does userspace-to-userspace copies directly. Likely because there's rarely a need for it?
-- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from hancockr@nospamshaw.ca Home Page: http://www.roberthancock.com/
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