On Fri, Apr 24, 2020 at 04:13:22PM +0100, Ben Hutchings wrote: > On Fri, 2020-04-24 at 15:52 +0200, Solar Designer wrote: > > On Fri, Apr 24, 2020 at 12:07:15AM +0100, Ben Hutchings wrote: > > > 3.16.83-rc1 review patch. If anyone has any objections, please let me know. > > > > I do. This patch is currently known-buggy, see this thread: > > > > https://www.openwall.com/lists/oss-security/2020/01/28/2 > > > > It is (partially) fixed with these newer commits in 5.5 and 5.5.2: > > > > commit d0cb50185ae942b03c4327be322055d622dc79f6 > > Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > Date: Sun Jan 26 09:29:34 2020 -0500 > > > > do_last(): fetch directory ->i_mode and ->i_uid before it's too late > > > > may_create_in_sticky() call is done when we already have dropped the > > reference to dir. > > > > Fixes: 30aba6656f61e (namei: allow restricted O_CREAT of FIFOs and regular files) > > Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > > > commit d76341d93dedbcf6ed5a08dfc8bce82d3e9a772b > > Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > Date: Sat Feb 1 16:26:45 2020 +0000 > > > > vfs: fix do_last() regression > > > > commit 6404674acd596de41fd3ad5f267b4525494a891a upstream. > [...] > > At least inclusion of the above fixes is mandatory for any backports. > > I know, and those are the next 2 patches in the series. Ah, then no objections from me. > > Also, I think no one has fixed the logic of may_create_in_sticky() so > > that it wouldn't unintentionally apply the "protection" when the file > > is neither a FIFO nor a regular file (something I found and mentioned in > > the oss-security posting above). > [...] > > I think the implementation of may_create_in_sticky() should be rewritten > > such that it'd directly correspond to the textual description in the > > comment above. As we've seen, trying to write the code "more optimally" > > resulted in its logic actually being different from the description. > > > > Meanwhile, I think backporting known-so-buggy code is a bad idea. > > I can see that it's not quite right, but does it matter in practice? > Directories and symlinks are handled separately; sockets can't be > opened anyway; block and character devices wonn't normally appear in a > sticky directory. Clearly, it doesn't matter all that much in practice - I'm not aware of anyone having complained about it causing issues on their system. I think it primarily mattered as an attack vector on the issue fixed with Al's commits above. I think we should nevertheless fix the code to match its intent and the comment, but meanwhile this isn't a blocker for the backport. Alexander
