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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id fe16-20020a056a002f1000b0063d6666ee4csm60165pfb.34.2023.05.17.15.58.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 May 2023 15:58:45 -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] pid: Replace struct pid 1-element array with flex-array Date: Wed, 17 May 2023 15:58:42 -0700 Message-Id: <20230517225838.never.965-kees@kernel.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3762; h=from:subject:message-id; bh=3VIzDUhfVBdAPvNGcA/e9saxBOkZkK+WtkJ5LzKNWZA=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBkZVwi+zjxK1xfiObiQXf1FPTnZFGfAWWd4T4RQyUa PXEWeOCJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZGVcIgAKCRCJcvTf3G3AJqyrEA CvteYy+49n7gSRsFTro4fVccGpHcRN/iGrbnn5vBk3RZ/nZr6tvvNCKV+vCDUj6XH1qkIKIGg4lKe3 0qbgGGC//Dr0Fj/iFSV/0WCgbeiuXH1bPtal/Ee2K9o9Gh+hggH459j/CijEDV/NxTemY5OAQSLPgA ibc+hJHMvn8zXGON5/E2l7TVmaycTExeRIRRPx/pM75xtiqez9so+Pa0AjBSrN5zkg32V5gzbbnrh1 sUsHy3SxFoVr0RplRzsoM71gkR4A2YXVpGVRv1m9tawuaGXMvtbV9T6arD989Xgormk13pxnFVztAp 91qpk2GYZ1hgGRQlBwBWDfNMdPRpptPoA1jSE4b1gwnvmCTPPUg703GFxDmspm1p96gf5qrp3bK3iz EQc94i0KrRDWZGL1FC1SpWn3F8mR6LLABhyNUetq0PjPX/NwtcJdeoQZ/4eCOQxLurC+k6Mc7SzK/K 4aKKSc0BRfUcnA/OeuIm34ZTCYaQfhMVZKc2ZzPSG7rWv647eoIqbqqYgO+FcT0gjQsTp8Gvo/hCEf iWQGZJRy7T28twW+zV1LyofKTUqPSB1o3NjyVn+y6kdGzQp67mFq59DrU/r77sGakJN+0oODtL1vc7 DnZcQtnRKAcS0FNpM/zMeldeAtrc5vPGrhMLIz8b4p6M0gPegStdTNGU80Og== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 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: https://lore.kernel.org/lkml/20230517-bushaltestelle-super-e223978c1ba6@brauner 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 Signed-off-by: Kees Cook Acked-by: Jeff Xu --- include/linux/pid.h | 2 +- kernel/pid.c | 13 ++++++++----- kernel/pid_namespace.c | 2 +- 3 files changed, 10 insertions(+), 7 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..f5008146e2e4 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -131,7 +131,7 @@ void free_pid(struct pid *pid) spin_lock_irqsave(&pidmap_lock, flags); for (i = 0; i <= pid->level; i++) { - struct upid *upid = pid->numbers + i; + struct upid *upid = &pid->numbers[i]; struct pid_namespace *ns = upid->ns; switch (--ns->pid_allocated) { case 2: @@ -265,7 +265,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, init_waitqueue_head(&pid->wait_pidfd); INIT_HLIST_HEAD(&pid->inodes); - upid = pid->numbers + ns->level; + upid = &pid->numbers[ns->level]; spin_lock_irq(&pidmap_lock); if (!(ns->pid_allocated & PIDNS_ADDING)) goto out_unlock; @@ -285,7 +285,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, out_free: spin_lock_irq(&pidmap_lock); while (++i <= ns->level) { - upid = pid->numbers + i; + upid = &pid->numbers[i]; idr_remove(&upid->ns->idr, upid->nr); } @@ -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 *)0, 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..ebb20091a9da 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((struct pid *)0, numbers, level + 1); mutex_lock(&pid_caches_mutex); /* Name collision forces to do allocation under mutex. */ if (!*pkc)