On Fri 11-04-08 21:26:56, Pavel Machek wrote: > On Thu 2008-04-10 16:27:00, Jan Kara 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? :) > > Yes. > > > > > > 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 > > Well, this race is more subtle - the window is just one instruction > > wide (stores to f_pos from CPU2 must come between the store of lower and > > upper 32-bits of f_pos on CPU1). And the only result is that f_pos has > > 32-bits from one file pointer and 32-bits from the other one. So I can > > hardly imagine this would be exploitable... > > Don't we have rlimit on max file size? I'd guess this could work > around it? There is this limit but AFAIK it limits max size of file you're able to create. And write/truncate checks already their local variable so the real value used later. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
