[PATCH] nilfs2: fix sysfs interface lifetime

[Ryusuke Konishi]

The current nilfs2 sysfs support has issues with the timing of creation
and deletion of sysfs entries, potentially leading to null pointer
dereferences, use-after-free, and lockdep warnings.

Some of the sysfs attributes for nilfs2 per-filesystem instance refer
to metadata file "cpfile", "sufile", or "dat", but
nilfs_sysfs_create_device_group that creates those attributes is
executed before the inodes for these metadata files are loaded, and
nilfs_sysfs_delete_device_group which deletes these sysfs entries is
called after releasing their metadata file inodes.

Therefore, access to some of these sysfs attributes may occur outside
of the lifetime of these metadata files, resulting in inode NULL pointer
dereferences or use-after-free.

In addition, the call to nilfs_sysfs_create_device_group() is made
during the locking period of the semaphore "ns_sem" of nilfs object,
so the shrinker call caused by the memory allocation for the sysfs
entries, may derive lock dependencies "ns_sem" -> (shrinker) ->
"locks acquired in nilfs_evict_inode()".

Since nilfs2 may acquire "ns_sem" deep in the call stack holding other
locks via its error handler __nilfs_error(), this causes lockdep to
report circular locking.  This is a false positive and no circular
locking actually occurs as no inodes exist yet when
nilfs_sysfs_create_device_group() is called.  Fortunately, the lockdep
warnings can be resolved by simply moving the call to
nilfs_sysfs_create_device_group() out of "ns_sem".

This fixes these sysfs issues by revising where the device's sysfs
interface is created/deleted and keeping its lifetime within the
lifetime of the metadata files above.

Reported-by: syzbot+979fa7f9c0d086fdc282@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/0000000000003414b505f7885f7e@xxxxxxxxxx
Reported-by: syzbot+5b7d542076d9bddc3c6a@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/0000000000006ac86605f5f44eb9@xxxxxxxxxx
Fixes: dd70edbde262 ("nilfs2: integrate sysfs support into driver")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Cc: Viacheslav Dubeyko <slava@xxxxxxxxxxx>
---
 fs/nilfs2/super.c     |  2 ++
 fs/nilfs2/the_nilfs.c | 12 +++++++-----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 1422b8ba24ed..77f1e5778d1c 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -482,6 +482,7 @@ static void nilfs_put_super(struct super_block *sb)
 		up_write(&nilfs->ns_sem);
 	}
 
+	nilfs_sysfs_delete_device_group(nilfs);
 	iput(nilfs->ns_sufile);
 	iput(nilfs->ns_cpfile);
 	iput(nilfs->ns_dat);
@@ -1105,6 +1106,7 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent)
 	nilfs_put_root(fsroot);
 
  failed_unload:
+	nilfs_sysfs_delete_device_group(nilfs);
 	iput(nilfs->ns_sufile);
 	iput(nilfs->ns_cpfile);
 	iput(nilfs->ns_dat);
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 3a4c9c150cbf..2894152a6b25 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -87,7 +87,6 @@ void destroy_nilfs(struct the_nilfs *nilfs)
 {
 	might_sleep();
 	if (nilfs_init(nilfs)) {
-		nilfs_sysfs_delete_device_group(nilfs);
 		brelse(nilfs->ns_sbh[0]);
 		brelse(nilfs->ns_sbh[1]);
 	}
@@ -305,6 +304,10 @@ int load_nilfs(struct the_nilfs *nilfs, struct super_block *sb)
 		goto failed;
 	}
 
+	err = nilfs_sysfs_create_device_group(sb);
+	if (unlikely(err))
+		goto sysfs_error;
+
 	if (valid_fs)
 		goto skip_recovery;
 
@@ -366,6 +369,9 @@ int load_nilfs(struct the_nilfs *nilfs, struct super_block *sb)
 	goto failed;
 
  failed_unload:
+	nilfs_sysfs_delete_device_group(nilfs);
+
+ sysfs_error:
 	iput(nilfs->ns_cpfile);
 	iput(nilfs->ns_sufile);
 	iput(nilfs->ns_dat);
@@ -697,10 +703,6 @@ int init_nilfs(struct the_nilfs *nilfs, struct super_block *sb, char *data)
 	if (err)
 		goto failed_sbh;
 
-	err = nilfs_sysfs_create_device_group(sb);
-	if (err)
-		goto failed_sbh;
-
 	set_nilfs_init(nilfs);
 	err = 0;
  out:
-- 
2.34.1