6.4-stable review patch. If anyone has any objections, please let me know.
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From: Aleksa Sarai cyphar@cyphar.com
[ Upstream commit 99f34659e78b9b781a3248e0b080b4dfca4957e2 ]
Patch series "memfd: cleanups for vm.memfd_noexec", v2.
The most critical issue with vm.memfd_noexec=2 (the fact that passing MFD_EXEC would bypass it entirely[1]) has been fixed in Andrew's tree[2], but there are still some outstanding issues that need to be addressed:
* vm.memfd_noexec=2 shouldn't reject old-style memfd_create(2) syscalls because it will make it far to difficult to ever migrate. Instead it should imply MFD_EXEC.
* The dmesg warnings are pr_warn_once(), which on most systems means that they will be used up by systemd or some other boot process and userspace developers will never see it.
- For the !(flags & (MFD_EXEC | MFD_NOEXEC_SEAL)) case, outputting a rate-limited message to the kernel log is necessary to tell userspace that they should add the new flags.
Arguably the most ideal way to deal with the spam concern[3,4] while still prompting userspace to switch to the new flags would be to only log the warning once per task or something similar. However, adding something to task_struct for tracking this would be needless bloat for a single pr_warn_ratelimited().
So just switch to pr_info_ratelimited() to avoid spamming the log with something that isn't a real warning. There's lots of info-level stuff in dmesg, it seems really unlikely that this should be an actual problem. Most programs are already switching to the new flags anyway.
- For the vm.memfd_noexec=2 case, we need to log a warning for every failure because otherwise userspace will have no idea why their previously working program started returning -EACCES (previously -EINVAL) from memfd_create(2). pr_warn_once() is simply wrong here.
* The racheting mechanism for vm.memfd_noexec makes it incredibly unappealing for most users to enable the sysctl because enabling it on &init_pid_ns means you need a system reboot to unset it. Given the actual security threat being protected against, CAP_SYS_ADMIN users being restricted in this way makes little sense.
The argument for this ratcheting by the original author was that it allows you to have a hierarchical setting that cannot be unset by child pidnses, but this is not accurate -- changing the parent pidns's vm.memfd_noexec setting to be more restrictive didn't affect children.
Instead, switch the vm.memfd_noexec sysctl to be properly hierarchical and allow CAP_SYS_ADMIN users (in the pidns's owning userns) to lower the setting as long as it is not lower than the parent's effective setting. This change also makes it so that changing a parent pidns's vm.memfd_noexec will affect all descendants, providing a properly hierarchical setting. The performance impact of this is incredibly minimal since the maximum depth of pidns is 32 and it is only checked during memfd_create(2) and unshare(CLONE_NEWPID).
* The memfd selftests would not exit with a non-zero error code when certain tests that ran in a forked process (specifically the ones related to MFD_EXEC and MFD_NOEXEC_SEAL) failed.
[1]: https://lore.kernel.org/all/ZJwcsU0vI-nzgOB_@codewreck.org/ [2]: https://lore.kernel.org/all/20230705063315.3680666-1-jeffxu@google.com/ [3]: https://lore.kernel.org/Y5yS8wCnuYGLHMj4@x1n/ [4]: https://lore.kernel.org/f185bb42-b29c-977e-312e-3349eea15383@linuxfoundation...
This patch (of 5):
Before this change, a test runner using this self test would see a return code of 0 when the tests using a child process (namely the MFD_NOEXEC_SEAL and MFD_EXEC tests) failed, masking test failures.
Link: https://lkml.kernel.org/r/20230814-memfd-vm-noexec-uapi-fixes-v2-0-7ff9e3e10... Link: https://lkml.kernel.org/r/20230814-memfd-vm-noexec-uapi-fixes-v2-1-7ff9e3e10... Fixes: 11f75a01448f ("selftests/memfd: add tests for MFD_NOEXEC_SEAL MFD_EXEC") Signed-off-by: Aleksa Sarai cyphar@cyphar.com Reviewed-by: Jeff Xu jeffxu@google.com Cc: "Christian Brauner (Microsoft)" brauner@kernel.org Cc: Daniel Verkamp dverkamp@chromium.org Cc: Dominique Martinet asmadeus@codewreck.org Cc: Kees Cook keescook@chromium.org Cc: Shuah Khan shuah@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/testing/selftests/memfd/memfd_test.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c index dba0e8ba002f8..7fc5d7c3bd65b 100644 --- a/tools/testing/selftests/memfd/memfd_test.c +++ b/tools/testing/selftests/memfd/memfd_test.c @@ -1202,7 +1202,24 @@ static pid_t spawn_newpid_thread(unsigned int flags, int (*fn)(void *))
static void join_newpid_thread(pid_t pid) { - waitpid(pid, NULL, 0); + int wstatus; + + if (waitpid(pid, &wstatus, 0) < 0) { + printf("newpid thread: waitpid() failed: %m\n"); + abort(); + } + + if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) != 0) { + printf("newpid thread: exited with non-zero error code %d\n", + WEXITSTATUS(wstatus)); + abort(); + } + + if (WIFSIGNALED(wstatus)) { + printf("newpid thread: killed by signal %d\n", + WTERMSIG(wstatus)); + abort(); + } }
/*