4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Miklos Szeredi <mszeredi@xxxxxxxxxx> commit 6becdb601bae2a043d7fb9762c4d48699528ea6e upstream. syzbot is reporting NULL pointer dereference at fuse_ctl_remove_conn() [1]. Since fc->ctl_ndents is incremented by fuse_ctl_add_conn() when new_inode() failed, fuse_ctl_remove_conn() reaches an inode-less dentry and tries to clear d_inode(dentry)->i_private field. Fix by only adding the dentry to the array after being fully set up. When tearing down the control directory, do d_invalidate() on it to get rid of any mounts that might have been added. [1] https://syzkaller.appspot.com/bug?id=f396d863067238959c91c0b7cfc10b163638cac6 Reported-by: syzbot <syzbot+32c236387d66c4516827@xxxxxxxxxxxxxxxxxxxxxxxxx> Fixes: bafa96541b25 ("[PATCH] fuse: add control filesystem") Cc: <stable@xxxxxxxxxxxxxxx> # v2.6.18 Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/fuse/control.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) --- a/fs/fuse/control.c +++ b/fs/fuse/control.c @@ -211,10 +211,11 @@ static struct dentry *fuse_ctl_add_dentr if (!dentry) return NULL; - fc->ctl_dentry[fc->ctl_ndents++] = dentry; inode = new_inode(fuse_control_sb); - if (!inode) + if (!inode) { + dput(dentry); return NULL; + } inode->i_ino = get_next_ino(); inode->i_mode = mode; @@ -228,6 +229,9 @@ static struct dentry *fuse_ctl_add_dentr set_nlink(inode, nlink); inode->i_private = fc; d_add(dentry, inode); + + fc->ctl_dentry[fc->ctl_ndents++] = dentry; + return dentry; } @@ -284,7 +288,10 @@ void fuse_ctl_remove_conn(struct fuse_co for (i = fc->ctl_ndents - 1; i >= 0; i--) { struct dentry *dentry = fc->ctl_dentry[i]; d_inode(dentry)->i_private = NULL; - d_drop(dentry); + if (!i) { + /* Get rid of submounts: */ + d_invalidate(dentry); + } dput(dentry); } drop_nlink(d_inode(fuse_control_sb->s_root));
