fuse: Fix oops at process_init_reply()

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-kernel@I-love.SKAURA.ne.jp>.

Reported-by: syzbot <syzbot+b62f08f4d5857755e3bc@syzkaller.appspotmail.com>
Fixes: e27c9d3877a0 ("fuse: fuse: add time_gran to INIT_OUT")
Cc: <stable@vger.kernel.org> # v3.19
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 11 insertions, 14 deletions

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index eeab70e7904d..0115c2f0a428 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -391,11 +391,6 @@ static void fuse_put_super(struct super_block *sb)
 {
         struct fuse_conn *fc = get_fuse_conn_super(sb);
 
-        fuse_send_destroy(fc);
-
-        fuse_abort_conn(fc, false);
-        fuse_wait_aborted(fc);
-
         mutex_lock(&fuse_mutex);
         list_del(&fc->entry);
         fuse_ctl_remove_conn(fc);
@@ -1212,16 +1207,25 @@ static struct dentry *fuse_mount(struct file_system_type *fs_type,
         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, false);
+                fuse_wait_aborted(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);
 }
 
@@ -1244,14 +1248,7 @@ static struct dentry *fuse_mount_blk(struct file_system_type *fs_type,
 
 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);
 }