[PATCH 3.16 073/328] fuse: Fix oops at process_init_reply()

[Ben Hutchings]

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszer...@redhat.com>

commit e8f3bd773d22f488724dffb886a1618da85c2966 upstream.

syzbot is hitting NULL pointer dereference at process_init_reply().
This is because deactivate_locked_super() is called before response for
initial request is processed.

Fix this by aborting and waiting for all requests (including FUSE_INIT)
before resetting fc->sb.

Original patch by Tetsuo Handa <penguin-ker...@i-love.skaura.ne.jp>.

Reported-by: syzbot <syzbot+b62f08f4d5857755e...@syzkaller.appspotmail.com>
Fixes: e27c9d3877a0 ("fuse: fuse: add time_gran to INIT_OUT")
Signed-off-by: Miklos Szeredi <mszer...@redhat.com>
[bwh: Backported to 3.16:
 - Drop second argument to fuse_abort_conn()
 - fuse_wait_aborted() is not needed]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -380,9 +380,6 @@ static void fuse_put_super(struct super_
 {
        struct fuse_conn *fc = get_fuse_conn_super(sb);
 
-       fuse_send_destroy(fc);
-
-       fuse_abort_conn(fc);
        mutex_lock(&fuse_mutex);
        list_del(&fc->entry);
        fuse_ctl_remove_conn(fc);
@@ -1124,16 +1121,24 @@ static struct dentry *fuse_mount(struct
        return mount_nodev(fs_type, flags, raw_data, fuse_fill_super);
 }
 
-static void fuse_kill_sb_anon(struct super_block *sb)
+static void fuse_sb_destroy(struct super_block *sb)
 {
        struct fuse_conn *fc = get_fuse_conn_super(sb);
 
        if (fc) {
+               fuse_send_destroy(fc);
+
+               fuse_abort_conn(fc);
+
                down_write(&fc->killsb);
                fc->sb = NULL;
                up_write(&fc->killsb);
        }
+}
 
+static void fuse_kill_sb_anon(struct super_block *sb)
+{
+       fuse_sb_destroy(sb);
        kill_anon_super(sb);
 }
 
@@ -1156,14 +1161,7 @@ static struct dentry *fuse_mount_blk(str
 
 static void fuse_kill_sb_blk(struct super_block *sb)
 {
-       struct fuse_conn *fc = get_fuse_conn_super(sb);
-
-       if (fc) {
-               down_write(&fc->killsb);
-               fc->sb = NULL;
-               up_write(&fc->killsb);
-       }
-
+       fuse_sb_destroy(sb);
        kill_block_super(sb);
 }