fuse: fix initial parallel dirops

If parallel dirops are enabled in FUSE_INIT reply, then first operation may
leave fi->mutex held.

Reported-by: syzbot <syzbot+3f7b29af1baa9d0a55be@syzkaller.appspotmail.com>
Fixes: 5c672ab3f0ee ("fuse: serialize dirops by default")
Cc: <stable@vger.kernel.org> # v4.7
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

3 files changed, 18 insertions, 10 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 56231b31f806..606909ed5f21 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -355,11 +355,12 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
         struct inode *inode;
         struct dentry *newent;
         bool outarg_valid = true;
+        bool locked;
 
-        fuse_lock_inode(dir);
+        locked = fuse_lock_inode(dir);
         err = fuse_lookup_name(dir->i_sb, get_node_id(dir), &entry->d_name,
                                &outarg, &inode);
-        fuse_unlock_inode(dir);
+        fuse_unlock_inode(dir, locked);
         if (err == -ENOENT) {
                 outarg_valid = false;
                 err = 0;
@@ -1340,6 +1341,7 @@ static int fuse_readdir(struct file *file, struct dir_context *ctx)
         struct fuse_conn *fc = get_fuse_conn(inode);
         struct fuse_req *req;
         u64 attr_version = 0;
+        bool locked;
 
         if (is_bad_inode(inode))
                 return -EIO;
@@ -1367,9 +1369,9 @@ static int fuse_readdir(struct file *file, struct dir_context *ctx)
                 fuse_read_fill(req, file, ctx->pos, PAGE_SIZE,
                                FUSE_READDIR);
         }
-        fuse_lock_inode(inode);
+        locked = fuse_lock_inode(inode);
         fuse_request_send(fc, req);
-        fuse_unlock_inode(inode);
+        fuse_unlock_inode(inode, locked);
         nbytes = req->out.args[0].size;
         err = req->out.h.error;
         fuse_put_request(fc, req);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 582b1756a011..f78e9614bb5f 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -975,8 +975,8 @@ int fuse_do_setattr(struct dentry *dentry, struct iattr *attr,
 
 void fuse_set_initialized(struct fuse_conn *fc);
 
-void fuse_unlock_inode(struct inode *inode);
-void fuse_lock_inode(struct inode *inode);
+void fuse_unlock_inode(struct inode *inode, bool locked);
+bool fuse_lock_inode(struct inode *inode);
 
 int fuse_setxattr(struct inode *inode, const char *name, const void *value,
                   size_t size, int flags);
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 0115c2f0a428..2dbd487390a3 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -357,15 +357,21 @@ int fuse_reverse_inval_inode(struct super_block *sb, u64 nodeid,
         return 0;
 }
 
-void fuse_lock_inode(struct inode *inode)
+bool fuse_lock_inode(struct inode *inode)
 {
-        if (!get_fuse_conn(inode)->parallel_dirops)
+        bool locked = false;
+
+        if (!get_fuse_conn(inode)->parallel_dirops) {
                 mutex_lock(&get_fuse_inode(inode)->mutex);
+                locked = true;
+        }
+
+        return locked;
 }
 
-void fuse_unlock_inode(struct inode *inode)
+void fuse_unlock_inode(struct inode *inode, bool locked)
 {
-        if (!get_fuse_conn(inode)->parallel_dirops)
+        if (locked)
                 mutex_unlock(&get_fuse_inode(inode)->mutex);
 }