Commit b69f0aeb authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds
Browse files

pid: Replace struct pid 1-element array with flex-array 

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:

  https://lore.kernel.org/lkml/20230517-bushaltestelle-super-e223978c1ba6@brauner



Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Xu <jeffxu@google.com>
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: default avatar <syzbot+ac3b41786a2d0565b6d5@syzkaller.appspotmail.com>
[brauner: dropped unrelated changes and remove 0 with NULL cast]
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 112e7e21

include/linux/pid.h

+1 −1
Original line number Diff line number Diff line
@@ -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;

kernel/pid.c

+5 −2
Original line number Diff line number Diff line
@@ -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((struct pid *)NULL, numbers, 1),

			__alignof__(struct pid),

			SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT,

			NULL);

}



static struct file *__pidfd_fget(struct task_struct *task, int fd)

kernel/pid_namespace.c

+1 −1
Original line number Diff line number Diff line
@@ -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((struct pid *)NULL, numbers, level + 1);

	mutex_lock(&pid_caches_mutex);

	/* Name collision forces to do allocation under mutex. */

	if (!*pkc)