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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id q5-20020a631f45000000b0051b7d83ff22sm10807050pgm.80.2023.06.30.11.04.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Jun 2023 11:04:26 -0700 (PDT) From: Kees Cook To: Christian Brauner Cc: Kees Cook , Jan Kara , Andreas Gruenbacher , Daniel Verkamp , "Paul E. McKenney" , Jeff Xu , Andrew Morton , Boqun Feng , Luis Chamberlain , Frederic Weisbecker , syzbot+ac3b41786a2d0565b6d5@syzkaller.appspotmail.com, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2] pid: Replace struct pid 1-element array with flex-array Date: Fri, 30 Jun 2023 11:04:22 -0700 Message-Id: <20230630180418.gonna.286-kees@kernel.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3300; i=keescook@chromium.org; h=from:subject:message-id; bh=MagSs+PRfh/Kgz8NQm3FmzmJ1z+sWa88uteLAKWLid4=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBknxklc/3X2AVavA3o7LUqjJp9Zl9UWIfvAUGOp vZQk32H6pGJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZJ8ZJQAKCRCJcvTf3G3A JtW1EACwkxvYH1JUSSTQ4A5vFqIK0eBAt9R3jddnmb58Md7SeX06isfl5qXfjjARFOGDoiCKowU O1aF0w7bu9vvDOzk2PIRVbuTFwuVpEb/n09QaySp6ZO0Ig1BcFXoDObSVflvCzMFtwH1dI8YxRj S2aDqdHavcGLwXNMVLK9rBFm5Z1FMKB4hkbl6M/4j5eTXmJEGElZu3i81M9P/MGxVA0b4d2mzda zYVMFMa0Vyg3saNNaWteXc1xUlb42dnW2hiw4igJVwQu/hXWHBrzl4wlvV/hGvmUuwXB1o2bD1D oYzw41MPbahBXZ6QPlnFYHUqHtcf4t2DX8dMt1snXmItFM36VZUiq7T5xyJDE2qaCWsrZO0a7yV K0d7lBW2n8PGZzeEru6YsF5MupfiIUu78v9xzrvY4DgTHqo0ysxL+3fA4hqrUm6te3OsDB3b2g5 iGhmAHvaVHmZuoCRDNdydEvTnsg/qaZR8e4FE77ePan4pTgOoYCtQpyk2yXfyjxWP/hKlfkQYBN 4Hg7T+cjI/dRa+mWki5vlcZg4hTjFFTdz0/EqXrWjCxlWhgECLRCAtbf76C49d6MjGYJiUe55zh zCCN2wNuxmJJMxN1NldWHdFTFNDDu/H/Rbwg7PS2cEUvB4iA/48EqnEaTwOBqossj3yn3d5ns9N l/PTrmM ooAdmK4Q== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org For pid namespaces, struct pid uses a dynamically sized array member, "numbers". This was implemented using the ancient 1-element fake flexible array, which has been deprecated for decades. Replace it with a C99 flexible array, refactor the array size calculations to use struct_size(), and address elements via indexes. Note that the static initializer (which defines a single element) works as-is, and requires no special handling. Without this, CONFIG_UBSAN_BOUNDS (and potentially CONFIG_FORTIFY_SOURCE) will trigger bounds checks when entering a pid namespace: https://lore.kernel.org/lkml/20230517-bushaltestelle-super-e223978c1ba6@brauner For example: unshare --fork --pid --mount-proc readlink /proc/self Cc: Christian Brauner Cc: Jan Kara Cc: Andreas Gruenbacher Cc: Daniel Verkamp Cc: "Paul E. McKenney" Cc: Jeff Xu Cc: Andrew Morton Cc: Boqun Feng Cc: Luis Chamberlain Cc: Frederic Weisbecker Reported-by: syzbot+ac3b41786a2d0565b6d5@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/000000000000c6de2a05fbdecbbb@google.com/ Acked-by: Jeff Xu Signed-off-by: Kees Cook --- v2: - drop pointer math to array index conversions (torvalds) - use struct_size_t now that it exists (torvalds) - updated commit log with reproducer example v1: https://lore.kernel.org/lkml/20230517225838.never.965-kees@kernel.org/ --- include/linux/pid.h | 2 +- kernel/pid.c | 7 +++++-- kernel/pid_namespace.c | 2 +- 3 files changed, 7 insertions(+), 4 deletions(-) diff --git a/include/linux/pid.h b/include/linux/pid.h index b75de288a8c2..653a527574c4 100644 --- a/include/linux/pid.h +++ b/include/linux/pid.h @@ -67,7 +67,7 @@ struct pid /* wait queue for pidfd notifications */ wait_queue_head_t wait_pidfd; struct rcu_head rcu; - struct upid numbers[1]; + struct upid numbers[]; }; extern struct pid init_struct_pid; diff --git a/kernel/pid.c b/kernel/pid.c index f93954a0384d..6a1d23a11026 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -656,8 +656,11 @@ void __init pid_idr_init(void) idr_init(&init_pid_ns.idr); - init_pid_ns.pid_cachep = KMEM_CACHE(pid, - SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT); + init_pid_ns.pid_cachep = kmem_cache_create("pid", + struct_size_t(struct pid, numbers, 1), + __alignof__(struct pid), + SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT, + NULL); } static struct file *__pidfd_fget(struct task_struct *task, int fd) diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index b43eee07b00c..0bf44afe04dd 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -48,7 +48,7 @@ static struct kmem_cache *create_pid_cachep(unsigned int level) return kc; snprintf(name, sizeof(name), "pid_%u", level + 1); - len = sizeof(struct pid) + level * sizeof(struct upid); + len = struct_size_t(struct pid, numbers, level + 1); mutex_lock(&pid_caches_mutex); /* Name collision forces to do allocation under mutex. */ if (!*pkc) -- 2.34.1