From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Subject: 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@xxxxxxxxxxxxxxxxxxxxxxxxx: 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@xxxxxxxxxxxxxxxx Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> Cc: Davidlohr Bueso <dbueso@xxxxxxx> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- ipc/msg.c | 2 +- ipc/sem.c | 2 +- ipc/shm.c | 2 ++ ipc/util.c | 10 ++++++++-- 4 files changed, 12 insertions(+), 4 deletions(-) --- a/ipc/msg.c~ipc-utilc-use-ipc_rcu_putref-for-failues-in-ipc_addid +++ a/ipc/msg.c @@ -163,7 +163,7 @@ static int newque(struct ipc_namespace * /* 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; } --- a/ipc/sem.c~ipc-utilc-use-ipc_rcu_putref-for-failues-in-ipc_addid +++ a/ipc/sem.c @@ -557,7 +557,7 @@ static int newary(struct ipc_namespace * /* 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; --- a/ipc/shm.c~ipc-utilc-use-ipc_rcu_putref-for-failues-in-ipc_addid +++ a/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; --- a/ipc/util.c~ipc-utilc-use-ipc_rcu_putref-for-failues-in-ipc_addid +++ a/ipc/util.c @@ -251,7 +251,9 @@ static inline int ipc_idr_alloc(struct i * 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, struc 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, struc 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, struc 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, struc } } if (idx < 0) { + new->deleted = true; spin_unlock(&new->lock); rcu_read_unlock(); return idx; _
