[Adding fsdevel list] On Tuesday 08 April 2008 10:05:47 am Meelis Roos 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 (*). 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). I think that it is better to live with tiny-race-on-broken-patterns rather than paying for synchronization which is not needed for correct paths. [*] file_pos_{read,write} (fs/read_write.c) are not called under lock (in sys_read, sys_write, ...), so even if f_pos is written atomically, you will be able to get races when accessing shared descriptor from different threads. I think that POSIX states, that behavior is undefined under these conditions. Best regards -- Michal Hocko SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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
