The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 8e04944f0ea8b838399049bdcda920ab36ae3b04 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Date: Wed, 4 Apr 2018 19:53:07 +0900 Subject: [PATCH] mm,vmscan: Allow preallocating memory for register_shrinker().
syzbot is catching so many bugs triggered by commit 9ee332d99e4d5a97 ("sget(): handle failures of register_shrinker()"). That commit expected that calling kill_sb() from deactivate_locked_super() without successful fill_super() is safe, but the reality was different; some callers assign attributes which are needed for kill_sb() after sget() succeeds.
For example, [1] is a report where sb->s_mode (which seems to be either FMODE_READ | FMODE_EXCL | FMODE_WRITE or FMODE_READ | FMODE_EXCL) is not assigned unless sget() succeeds. But it does not worth complicate sget() so that register_shrinker() failure path can safely call kill_block_super() via kill_sb(). Making alloc_super() fail if memory allocation for register_shrinker() failed is much simpler. Let's avoid calling deactivate_locked_super() from sget_userns() by preallocating memory for the shrinker and making register_shrinker() in sget_userns() never fail.
[1] https://syzkaller.appspot.com/bug?id=588996a25a2587be2e3a54e8646728fb9cae44e...
Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Reported-by: syzbot syzbot+5a170e19c963a2e0df79@syzkaller.appspotmail.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Michal Hocko mhocko@suse.com Signed-off-by: Al Viro viro@zeniv.linux.org.uk
diff --git a/fs/super.c b/fs/super.c index 5fa9a8d8d865..122c402049a2 100644 --- a/fs/super.c +++ b/fs/super.c @@ -167,6 +167,7 @@ static void destroy_unused_super(struct super_block *s) security_sb_free(s); put_user_ns(s->s_user_ns); kfree(s->s_subtype); + free_prealloced_shrinker(&s->s_shrink); /* no delays needed */ destroy_super_work(&s->destroy_work); } @@ -252,6 +253,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags, s->s_shrink.count_objects = super_cache_count; s->s_shrink.batch = 1024; s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE; + if (prealloc_shrinker(&s->s_shrink)) + goto fail; return s;
fail: @@ -518,11 +521,7 @@ struct super_block *sget_userns(struct file_system_type *type, hlist_add_head(&s->s_instances, &type->fs_supers); spin_unlock(&sb_lock); get_filesystem(type); - err = register_shrinker(&s->s_shrink); - if (err) { - deactivate_locked_super(s); - s = ERR_PTR(err); - } + register_shrinker_prepared(&s->s_shrink); return s; }
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h index 388ff2936a87..6794490f25b2 100644 --- a/include/linux/shrinker.h +++ b/include/linux/shrinker.h @@ -75,6 +75,9 @@ struct shrinker { #define SHRINKER_NUMA_AWARE (1 << 0) #define SHRINKER_MEMCG_AWARE (1 << 1)
-extern int register_shrinker(struct shrinker *); -extern void unregister_shrinker(struct shrinker *); +extern int prealloc_shrinker(struct shrinker *shrinker); +extern void register_shrinker_prepared(struct shrinker *shrinker); +extern int register_shrinker(struct shrinker *shrinker); +extern void unregister_shrinker(struct shrinker *shrinker); +extern void free_prealloced_shrinker(struct shrinker *shrinker); #endif diff --git a/mm/vmscan.c b/mm/vmscan.c index 8b920ce3ae02..9b697323a88c 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -303,7 +303,7 @@ unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone /* * Add a shrinker callback to be called from the vm. */ -int register_shrinker(struct shrinker *shrinker) +int prealloc_shrinker(struct shrinker *shrinker) { size_t size = sizeof(*shrinker->nr_deferred);
@@ -313,10 +313,29 @@ int register_shrinker(struct shrinker *shrinker) shrinker->nr_deferred = kzalloc(size, GFP_KERNEL); if (!shrinker->nr_deferred) return -ENOMEM; + return 0; +} + +void free_prealloced_shrinker(struct shrinker *shrinker) +{ + kfree(shrinker->nr_deferred); + shrinker->nr_deferred = NULL; +}
+void register_shrinker_prepared(struct shrinker *shrinker) +{ down_write(&shrinker_rwsem); list_add_tail(&shrinker->list, &shrinker_list); up_write(&shrinker_rwsem); +} + +int register_shrinker(struct shrinker *shrinker) +{ + int err = prealloc_shrinker(shrinker); + + if (err) + return err; + register_shrinker_prepared(shrinker); return 0; } EXPORT_SYMBOL(register_shrinker);