On Fri, Jan 9, 2015 at 3:12 PM, Rich Felker <dalias@xxxxxxxxxx> wrote: > On Fri, Jan 09, 2015 at 10:57:43PM +0000, Al Viro wrote: >> On Fri, Jan 09, 2015 at 05:42:52PM -0500, Rich Felker wrote: >> >> > Here's a very simple way it could work -- it could put the O_PATH fd >> > on a previously-unused fd number, and put a special flag on the fd, >> > like FD_CLOEXEC, but that causes the kernel to close it whenever it's >> > opened. The pathname passed could then simply be /dev/fd/%d or >> > /proc/self/fd/%d, and although this is presently dependent on /proc >> > being mounted, virtual /dev/fd/* could someday be something completely >> > independent of procfs. The kernel keeps all the freedom to choose how >> > to pass the name to the interpreter. I'm not proposing any kernel >> > API/ABI lock-in and I'm with you in opposing such lock-in. >> >> Huh? open() on procfs symlinks does *NOT* work the way - the symlink is >> traversed and after that point there is no information whatsoever how we >> got to that vfsmount/dentry pair. I can imagine several kludges that would >> work, but they are unspeakably ugly, and do_last() is already far too >> convoluted as it is. > > I'm not sure where you're disagreeing with me. open of procfs symlinks > does not resolve the symlink and open the resulting pathname. They are > "magic symlinks" which are bound to the inode of the open file. I > don't see why this action, which is already special for magic > symlinks, can't check a flag on the magic symlink and possibly close > the corresponding file descriptor as part of its action. > > In any case, whether/how fexecve works with interpreters is something > the kernel can change without breaking userspace expectations. My goal > is to avoid creating any new API/ABI requirement here. > I think that, if we really want to support clean fexecve on O_CLOEXEC scripts some day, the right way to do it is to fix the script interface for real. Have a special flag in the headers of script interpreters that support a new interface that says "when I'm a script interpreter, I expect an auxv entry AT_SCRIPT_FD with an open fd with CLOEXEC set". Then we can directly exec scripts by fd, even with O_CLOEXEC set, without any races. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
