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authorTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>2018-04-04 19:53:07 +0900
committerAl Viro <viro@zeniv.linux.org.uk>2018-04-16 02:06:47 -0400
commit8e04944f0ea8b838399049bdcda920ab36ae3b04 (patch)
tree830ce2c35100627212caaf732396cafd7bfc1dc8 /fs
parent4a3877c4cedd95543f8726b0a98743ed8db0c0fb (diff)
downloadlinux-8e04944f0ea8b838399049bdcda920ab36ae3b04.tar.bz2
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=588996a25a2587be2e3a54e8646728fb9cae44e7 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>
Diffstat (limited to 'fs')
-rw-r--r--fs/super.c9
1 files changed, 4 insertions, 5 deletions
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 @@ retry:
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;
}