Messages in this thread | | | Date | Tue, 22 Apr 2014 14:44:50 +0200 | Subject | Re: [RFC 2/2] fs,proc: Respect FMODE_WRITE when opening /proc/pid/fd/N | From | David Herrmann <> |
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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?
> 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); 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).
Thanks David
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