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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id j4-20020a170902da8400b0017eb2d62bbesm6014743plx.99.2022.10.06.01.27.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Oct 2022 01:27:39 -0700 (PDT) From: Kees Cook To: Eric Biederman Cc: Kees Cook , Jorge Merlino , Al Viro , "Christian Brauner (Microsoft)" , Thomas Gleixner , Andy Lutomirski , Sebastian Andrzej Siewior , Andrew Morton , John Johansen , Paul Moore , James Morris , "Serge E. Hallyn" , Stephen Smalley , Eric Paris , Richard Haines , Casey Schaufler , Xin Long , "David S. Miller" , Todd Kjos , Ondrej Mosnacek , Prashanth Prahlad , Micah Morton , Fenghua Yu , Andrei Vagin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH 0/2] fs/exec: Explicitly unshare fs_struct on exec Date: Thu, 6 Oct 2022 01:27:33 -0700 Message-Id: <20221006082735.1321612-1-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1735; h=from:subject; bh=8JXgAWBrUCWySpKU2akeepLoIo1ngoevmTcyBBHjAt0=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBjPpF3qES4cYgipY9Yg66d58hnI1s34HzpasPEsrcs AdJZe+KJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYz6RdwAKCRCJcvTf3G3AJvuPD/ sEFuqb2jJFVbuCOokYGoNQsjw0c9Jmc0XwKWYipIHX1SMMd2WkotpH8FIpOwZ4FyBWjaC7R1DvZeLq wpDvCMawMGqka4y/+7g515eraCONHoJNn0oj2fukbMyqECfinzpw5/d4oLtWkFvyiE4HCoYP/6kmKK 0R8NWKCoSDvGWq7Usrp1Ra1BUXvG1UZHbw7j4g9ItLOqgALdmExlSixoeozIYoogVyhKH0WKOVKYth 6CRkWQcZ/xYBwGsWX7qmIQbUWoTiCbt1fTDMB4IZf5Cn6zrxQL7XNaEUK5j1dcf9ZKTqux5G32e7Of 81YIltR3K2wnhH4qLNhRec5guNWZ3ILs2c6YZDh2TFkb9rGX4cajkAKcAV/vMrP3Kjr9vZKHBdRtPd rsnr6zOL9FYSWR+4i8yhrgvEsVDvenhdlfscGxtpeM7wExsxxiICpUQTRZxDvkLJhahLlKMWnxHm1y N2eVoeyvRe9j7JMCjfOqfKyKLHBZfoqFWmfSVi88JV/Gr797J1kRDlGaszfz7SxKiINHJQK1POiTOc Eic3WPt1/rLSOcANGevkuLKRQkzZ0waIkzKR/ddRrxXv/kszRk/EvoQpjPnt81zaCBe+7jXDXKm4N3 wH+iXTk/Lc17bTuykzisNHzRgsTueD8b0Epfk0nQ+rUUKSa20mimgCQla6rA== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi, These changes seek to address an issue reported[1] by Jorge Merlino where high-thread-count processes would sometimes fail to setuid during a setuid execve(). It looks to me like the solution is to explicitly do an unshare_fs(), which should almost always be a no-op. Current testing seems to indicate that only the swapper->init exec triggers this condition (and I'm unclear on whether that's expected or undesirable). This has only received very light testing so far, but I wanted to share it so other folks could look it over. Jorge, can you test with these patches? Your PoC triggered immediately for me on an unpatched kernel, and did not trigger on a patched one. I added this patch on top of the series to see if the code ever fired: Thanks! -Kees [1] https://lore.kernel.org/lkml/20220910211215.140270-1-jorge.merlino@canonical.com/ Kees Cook (2): fs/exec: Explicitly unshare fs_struct on exec exec: Remove LSM_UNSAFE_SHARE fs/exec.c | 26 ++++------------ fs/fs_struct.c | 1 - include/linux/fdtable.h | 1 + include/linux/fs_struct.h | 1 - include/linux/security.h | 5 ++- kernel/fork.c | 62 ++++++++++++++++++++++++++------------ security/apparmor/domain.c | 5 --- security/selinux/hooks.c | 10 ------ 8 files changed, 51 insertions(+), 60 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 53b7248f7a4b..3c197d9d8daa 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -3113,6 +3113,7 @@ int unshare_fs(void) if (error || !new_fs) return error; + pr_notice("UNSHARE of \"%s\" [%d]\n", current->comm, current->pid); unshare_fs_finalize(&new_fs); if (new_fs)