Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH v2] pid: Replace struct pid 1-element array with flex-array | Date | Fri, 30 Jun 2023 11:04:22 -0700 |
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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 <brauner@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Andreas Gruenbacher <agruenba@redhat.com> Cc: Daniel Verkamp <dverkamp@chromium.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Jeff Xu <jeffxu@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Frederic Weisbecker <frederic@kernel.org> Reported-by: syzbot+ac3b41786a2d0565b6d5@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/000000000000c6de2a05fbdecbbb@google.com/ Acked-by: Jeff Xu <jeffxu@google.com> Signed-off-by: Kees Cook <keescook@chromium.org> --- 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
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