Messages in this thread | | | Date | Tue, 22 Apr 2014 16:31:52 +0200 | From | Pavel Machek <> | Subject | Re: [RFC 2/2] fs,proc: Respect FMODE_WRITE when opening /proc/pid/fd/N |
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Hi!
> On Mon, Apr 21, 2014 at 6:22 PM, Andy Lutomirski <luto@amacapital.net> wrote: > > This patch does this: > > I can see _what_ the patch does, but your patch lacks any discussion > _why_ it is needed. Can you provide at least one real example where > this fixes a security issue?
Such as here?
http://www.securityfocus.com/archive/1/507386
> > This may break userspace. If so, I would guess that anything broken > > by it is either an actual exploit or is so broken that it doesn't > > deserve to continue working. If it breaks something important, then > > maybe it will need a sysctl. > > This patch breaks the following use-case: > > fd = open("/run", O_RDWR | O_TMPFILE); > sprintf(path, "/proc/self/fd/%d", fd); > fd2 = open(buf, O_RDONLY);
You meant open(path, ) here?
> sprintf(path, "/proc/self/fd/%d", fd2); > linkat(AT_FDCWD, path, AT_FDCWD, "/run/some_lock_file", AT_FOLLOW_SYMLINK); > > I mean I explicitly create the object as _writable_ but then keep a > read-only descriptor for debugging purposes (to make sure that the > program no longer writes to the file). This is no security feature, > but only a safety feature in case something goes wrong. But I still > want to be able to create hard-links (I _do_ have write-permissions on > the object/inode).
Does some real code do it? I believe this deserves to be broken -- you explicitely opened that read-only...
Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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