On Tue, Nov 3, 2015 at 10:58 PM, Willy Tarreau <w@xxxxxx> wrote: > On Tue, Nov 03, 2015 at 03:29:55PM -0800, Kees Cook wrote: >> Using "write" does kill the set-gid bit. I haven't looked at >> why. >> Al or anyone else, is there a meaningful distinction here? > > I remember this one, I got caught once while trying to put a shell into > a suid-writable file to get some privileges someone forgot to offer me :-) > > It's done by should_remove_suid() which is called upon write() and truncate(). > >> Should the >> mmap MAP_SHARED-write trigger the loss of the set-gid bit too? While >> holding the file open with either open or mmap, I get a Text-in-use >> error, so I would kind of expect the same behavior between either >> close() and munmap(). I wonder if this is a bug, and if so, then your >> link patch is indeed useful again. :) > > I don't see how this could be done with mmap(). Maybe we have a way to know > when the first write is performed via this path, I have no idea. do_wp_page might be a decent bet. --Andy -- 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
