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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 /mm
parent4a3877c4cedd95543f8726b0a98743ed8db0c0fb (diff)
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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 'mm')
-rw-r--r--mm/vmscan.c21
1 files changed, 20 insertions, 1 deletions
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);