On Thu, Oct 30, 2014 at 3:58 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, Oct 30, 2014 at 3:48 PM, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: >> >> Agreed. Will apply and add the stable cc. > > Ho humm. Thinking about this some more, I'm starting to wonder. Not > about this patch per se (open on a newly created file should indeed > succeed regardless), but about the horrible glibc behavior of screwing > up the third argument. > > If you want to do O_TMPFILE + linkat() (or some eventual future > flink()), the mode really matters. So this idiotic glibc behavior of > only forwarding the third argument if O_CREAT is set seems to be a > bug. Yes, there definitely is a glibc bug: a fix is being worked on and it looks like it will go in. The change replaces the test for O_CREAT by a test for either O_CREAT or O_TMPFILE. > Why the hell does glibc think it's a good idea to intersect system > call semantics? It's not a good idea - it's just stupid in the > extreme. And in this case it seems to actively breaks things. What Andy said: it's the most portable, because of the optional last argument, if you have a bunch of wrappers for open and openat written in C, which they do. Some of these wrappers are for statically checking that the mode argument is present when necessary (using __builtin_constant_p, __builtin_va_arg_pack, and friends), and to "fortify" the code against a malicious (?) injection of O_CREAT in a code path that didn't have it at compile time (where flags was a build constant). Other wrappers add O_LARGEFILE. One wrapper for openat checks that dirfd is a directory (no idea why, as the kernel does the same check -- without a race; maybe to try to guarantee ENOTDIR on some old kernel version? It's been here since 2005, when openat was added to glibc). -- Eric Rannaud <e@xxxxxxxxxxxxxxxx> Nanocritical, CEO -- 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
