sysfs: handle failure path correctly for readdir()

commit e5110f411d2ee35bf8d202ccca2e89c633060dca upstream.

In case of 'if (filp->f_pos ==  0 or 1)' of sysfs_readdir(),
the failure from filldir() isn't handled, and the reference counter
of the sysfs_dirent object pointed by filp->private_data will be
released without clearing filp->private_data, so use after free
bug will be triggered later.

This patch returns immeadiately under the situation for fixing the bug,
and it is reasonable to return from readdir() when filldir() fails.

Reported-by: Dave Jones <davej@redhat.com>
Tested-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 309d21a..3899e24 100644 (file)
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -985,6 +985,8 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
                ino = parent_sd->s_ino;
                if (filldir(dirent, ".", 1, filp->f_pos, ino, DT_DIR) == 0)
                        filp->f_pos++;
+               else
+                       return 0;
        }
        if (filp->f_pos == 1) {
                if (parent_sd->s_parent)
@@ -993,6 +995,8 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
                        ino = parent_sd->s_ino;
                if (filldir(dirent, "..", 2, filp->f_pos, ino, DT_DIR) == 0)
                        filp->f_pos++;
+               else
+                       return 0;
        }
        mutex_lock(&sysfs_mutex);
        for (pos = sysfs_dir_pos(ns, parent_sd, filp->f_pos, pos);