On Thu, 7 Nov 2019 21:06:14 -0500 Joel Fernandes joel@joelfernandes.org wrote:
On Thu, Nov 07, 2019 at 05:00:23PM -0800, Andrew Morton wrote:
On Thu, 7 Nov 2019 14:53:54 -0500 "Joel Fernandes (Google)" joel@joelfernandes.org wrote:
F_SEAL_FUTURE_WRITE has unexpected behavior when used with MAP_PRIVATE: A private mapping created after the memfd file that gets sealed with F_SEAL_FUTURE_WRITE loses the copy-on-write at fork behavior, meaning children and parent share the same memory, even though the mapping is private.
That sounds fairly serious. Should this be backported into -stable kernels?
Yes, it should be.
I added
Fixes: ab3948f58ff84 ("mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd") Cc: stable@vger.kernel.org
The F_SEAL_FUTURE_WRITE feature was introduced in v5.1 so v5.3.x stable kernels would need a backport. I can submit a backport tomorrow unless we are Ok with stable automatically picking it up (I believe the stable folks "auto select" fixes which should detect this is a fix since I have said it is a fix in the subject line).
The Cc:stable tag should trigger the appropriate actions, assisted by the Fixes:. I doubt if "fix" in the Subject has much effect.