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    SubjectRe: file offset corruption on 32-bit machines?
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    On Thursday 10 April 2008 04:01:27 pm Jiri Kosina wrote:
    > On Thu, 10 Apr 2008, Michal Hocko wrote:
    > > > Jeff Robertson analyzes the behaviour of different operating systems'
    > > > 64-bit file offset implementation and concludes that on 32-bit
    > > > machines, Linux and Solaris lack any locking to keep the two 32-bit
    > > > halves in sync and this could cause rare file offset corruption.
    > > > http://jeffr-tech.livejournal.com/21014.html
    > >
    > > AFAICS, this race is theoretically possible, but it is very hard (almost
    > > impossible) to trigger with a sane file usage pattern. Note that you
    > > have to access shared struct file (same file descriptor) in different
    > > threads which should be synchronized by caller anyway (*).
    >
    > ... but not in cases the caller is an intentionally evil code, right? :)

    Ok, but evil code needs to have access to your struct file and in such a case
    he can do worse things ;)
    Or do you have some concrete (innocent looking) example?

    >
    > > I also don't see any security implications from this race, but maybe
    > > someone with more knowlage about fs can see (f_pos is used at many
    > > places in the kernel code).
    >
    > The f_pos races are in fact exploitable, we've already been there. See
    > for example http://www.isec.pl/vulnerabilities/isec-0016-procleaks.txt

    This is different race with file position IMO. If I understand the report
    correctly, problem was with sleeping copy_to_user while the f_pos has
    changed.

    Best regards
    --
    Michal Hocko
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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