filepath-securejoin v0.3 gave us a much safer re-open primitive, we
should use it to avoid any theoretical attacks. Rather than using it
direcly, add a small pathrs wrapper to make libpathrs migrations in the
future easier...
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Prior to kernel Linux 5.5, F_SEAL_FUTURE_WRITE has a bug which maps
memory as shared between processes even if it is set as private. See
kernel commit 05d351102dbe ("mm, memfd: fix COW issue on MAP_PRIVATE and
F_SEAL_FUTURE_WRITE mappings") for more details.
According to the fcntl(2) man pages, F_SEAL_WRITE is enough:
> Furthermore, trying to create new shared, writable memory-mappings via
> mmap(2) will also fail with EPERM.
>
> Using the F_ADD_SEALS operation to set the F_SEAL_WRITE seal fails
> with EBUSY if any writable, shared mapping exists. Such mappings must
> be unmapped before you can add this seal.
F_SEAL_FUTURE_WRITE only makes sense if a read-write shared mapping in
one process should be read-only in another process. This is not case for
runc, especially not for the /proc/self/exe we are protecting.
Signed-off-by: Tomasz Duda <tomaszduda23@gmail.com>
(cyphar: improve the comment regarding F_SEAL_FUTURE_WRITE)
(cyphar: improve commit message)
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
The "dmz" name was originally used because the libcontainer/dmz package
housed the runc-dmz binary, but since we removed it in commit
871057d863 ("drop runc-dmz solution according to overlay solution")
the name is an anachronism and we should just give it a more
self-explanatory name.
So, call it libcontainer/exeseal because the purpose of the package is
to provide tools to seal /proc/self/exe against attackers.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Kir Kolyshkin