Message ID | 20230630180418.gonna.286-kees@kernel.org (mailing list archive) |
---|---|
State | Superseded |
Headers | show |
Series | [v2] pid: Replace struct pid 1-element array with flex-array | expand |
On 6/30/23 12:04, Kees Cook wrote: > 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> I would vote in favor of the array over the pointer notation, but anyway... we need to land this change, and that's what matters. Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org> Thanks! -- Gustavo > --- > 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)
On Fri, Jun 30, 2023 at 11:04:22AM -0700, Kees Cook wrote: > 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 Thanks for that. Linus already merged the other version I gave him with his requested changes but without your struct_size_t() update. It didn't exist when you originally sent that patch afaiu and I just realized that it existed right now. In any case, I'm just going to send a trivial follow-up patch switching the two places to struct_size_t(). Thanks, Kees!
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)