On Wed, Jul 07, 2010 at 07:33:11PM +0200, Christoph Hellwig wrote: > On Wed, Jul 07, 2010 at 10:31:37AM -0700, Linus Torvalds wrote: > > On Wed, Jul 7, 2010 at 10:11 AM, Ulrich Drepper <drepper@xxxxxxxxxx> wrote: > > > > > > How does this work with old kernels which didn't initialize f_spare? > > > > Some of the compat layers (and older kernels) don't copy the f_spare > > values, so user space should clear the field before doing the system > > call, and you should be ok. > > > > There should be no actual _uninitialized_ values copied from the > > kernel. IOW, either the kernel writes zero, or it doesn't write > > anything at all. Anything else would be a security issue anyway (ie > > kernel stack data leak). Afaik, no kernel does that. > > Sometime before 2.4.0 (I posted the exact release in the previous > thread) the kernel initalized unused fields to 0xff. So if we want to > support these kernels it is an issue. glibc could just set 2.4.0 as the oldest version to test ST_VALID against. I think most distros compile it to support no older than 2.6.something kernels anyway. Should we not allow glibc to assume the mapping is 1:1 except ST_VALID? If other spare fields may be used in future, this could be the best place to do versioning or otherwise make use of some bits. Possibly a couple of bits could be used for version number. -- 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
