On Mon, Nov 3, 2014 at 3:42 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On Mon, Nov 3, 2014 at 7:20 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: >> On Mon, Nov 03, 2014 at 11:48:23AM +0000, David Drysdale wrote: >>> Add a new O_BENEATH flag for openat(2) which restricts the >>> provided path, rejecting (with -EACCES) paths that are not beneath >>> the provided dfd. In particular, reject: >>> - paths that contain .. components >>> - paths that begin with / >>> - symlinks that have paths as above. >> >> Yecch... The degree of usefulness aside (and I'm not convinced that it >> is non-zero), > > This is extremely useful in conjunction with seccomp. Yes, that was my understanding of how the Chrome[OS] folk wanted to use it. >> WTF pass one bit out of nameidata->flags in a separate argument? I'll shift to using nd->flags; not sure what I was thinking of there. (It *might* have made more sense in the full patchset this was extracted from but it certainly doesn't look sensible in this narrower context.) >> Through the mutual recursion, no less... And then you are not even attempting >> to detect symlinks that are not followed by interpretation of _any_ pathname. > > How many symlinks like that are there? Is there anything except > nd_jump_link users? All of those are in /proc. Arguably O_BENEATH > should prevent traversal of all of those links. > > --Andy On a quick search, the 2 users of nd_jump_link (namely proc_pid_follow_link and proc_ns_follow_link) seem to be the only implementations of inode_operations->follow_link that don't just call nd_set_link(). So disallowing that for O_BENEATH might give sensible behaviour. -- 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
