Messages in this thread | | | Date | Tue, 27 Dec 2011 15:23:44 -0800 | From | Andrew Morton <> | Subject | Re: [patch 1/4] Add routine for generating an ID for kernel pointer |
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On Fri, 23 Dec 2011 16:47:42 +0400 Cyrill Gorcunov <gorcunov@openvz.org> wrote:
> The routine XORs the given pointer with a random value > producing an ID (32 or 64 bit, depending on the arch). > > Since it's a valuable information -- only CAP_SYS_ADMIN > is allowed to obtain it. > > - Tejun worried about the single poison value was a weak side - > leaking one makes all the IDs vulnerable. To address this > several poison values - one per object type - are introduced. > They are stored in a plain array. > - Pekka proposed to initialized poison values in the late_initcall callback > - ... and move the code to mm/util.c
I'm trying to remember what this is all about, and I don't want to have to remember all the discussion from last time this came up!
Please, do cover all this in the changelogs: tell us what the code is all for and try to capture the design decisions thus far. It's a useful reminder for current reviewers and is very valuable for new reviewers.
The root-only restriction sounds like a pretty bad one. I suspect it really isn't that bad but again, the changelog should discuss the pros and cons here.
A thought: if all we're trying to do here is to check for the sameness of objects, can we push the comparison into the kernel so we don't have this exporting-sensitive-info problem at all? Just return a boolean to userspace?
Something like
int sys_pid_fields_equal(pid_t pid1, pid_t pid2, enum pid_field field_id);
?
For /proc/pid/fdinfo/* userspace can open /proc/pid1/fdinfo/0 and /proc/pid2/fdinfo/0 and call sys_are_these_files_the_same(fd1, fd2, ...).
Perhaps sys_pid_fields_equal() can use sys_are_these_files_the_same() as well, if we can think up a way of passing it two fds to represent the two pids.
Have a think about it ;)
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