From 39cfffd774a2e8818250360a3e028b5eac9d5392 Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Tue, 21 Aug 2018 22:01:29 -0700 Subject: [PATCH] ipc/util.c: use ipc_rcu_putref() for failues in ipc_addid() ipc_addid() is impossible to use: - for certain failures, the caller must not use ipc_rcu_putref(), because the reference counter is not yet initialized. - for other failures, the caller must use ipc_rcu_putref(), because parallel operations could be ongoing already. The patch cleans that up, by initializing the refcount early, and by modifying all callers. The issues is related to the finding of syzbot+2827ef6b3385deb07eaf@syzkaller.appspotmail.com: syzbot found an issue with reading kern_ipc_perm.seq, here both read and write to already released memory could happen. Link: http://lkml.kernel.org/r/20180712185241.4017-4-manfred@colorfullife.com Signed-off-by: Manfred Spraul Cc: Dmitry Vyukov Cc: Kees Cook Cc: Davidlohr Bueso Cc: Davidlohr Bueso Cc: Herbert Xu Cc: Michael Kerrisk Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/msg.c | 2 +- ipc/sem.c | 2 +- ipc/shm.c | 2 ++ ipc/util.c | 10 ++++++++-- 4 files changed, 12 insertions(+), 4 deletions(-) diff --git a/ipc/msg.c b/ipc/msg.c index 7cb89a9b24e2..3132aa27ff88 100644 --- a/ipc/msg.c +++ b/ipc/msg.c @@ -163,7 +163,7 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params) /* ipc_addid() locks msq upon success. */ retval = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni); if (retval < 0) { - call_rcu(&msq->q_perm.rcu, msg_rcu_free); + ipc_rcu_putref(&msq->q_perm, msg_rcu_free); return retval; } diff --git a/ipc/sem.c b/ipc/sem.c index 18e50f464f76..8e72037b894a 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -557,7 +557,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params) /* ipc_addid() locks sma upon success. */ retval = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni); if (retval < 0) { - call_rcu(&sma->sem_perm.rcu, sem_rcu_free); + ipc_rcu_putref(&sma->sem_perm, sem_rcu_free); return retval; } ns->used_sems += nsems; diff --git a/ipc/shm.c b/ipc/shm.c index b3b089315d3b..6e7bd9830549 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -684,6 +684,8 @@ no_id: if (is_file_hugepages(file) && shp->mlock_user) user_shm_unlock(size, shp->mlock_user); fput(file); + ipc_rcu_putref(&shp->shm_perm, shm_rcu_free); + return error; no_file: call_rcu(&shp->shm_perm.rcu, shm_rcu_free); return error; diff --git a/ipc/util.c b/ipc/util.c index e5c9e2b2e4c4..465bbd21d234 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -251,7 +251,9 @@ static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new) * Add an entry 'new' to the ipc ids idr. The permissions object is * initialised and the first free entry is set up and the id assigned * is returned. The 'new' entry is returned in a locked state on success. + * * On failure the entry is not locked and a negative err-code is returned. + * The caller must use ipc_rcu_putref() to free the identifier. * * Called with writer ipc_ids.rwsem held. */ @@ -261,6 +263,9 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) kgid_t egid; int idx, err; + /* 1) Initialize the refcount so that ipc_rcu_putref works */ + refcount_set(&new->refcount, 1); + if (limit > IPCMNI) limit = IPCMNI; @@ -269,9 +274,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) idr_preload(GFP_KERNEL); - refcount_set(&new->refcount, 1); spin_lock_init(&new->lock); - new->deleted = false; rcu_read_lock(); spin_lock(&new->lock); @@ -279,6 +282,8 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) new->cuid = new->uid = euid; new->gid = new->cgid = egid; + new->deleted = false; + idx = ipc_idr_alloc(ids, new); idr_preload_end(); @@ -291,6 +296,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) } } if (idx < 0) { + new->deleted = true; spin_unlock(&new->lock); rcu_read_unlock(); return idx; -- 2.30.2