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    Subject[PATCH 5.17 187/219] cifs: verify that tcon is valid before dereference in cifs_kill_sb
    Date
    From: Ronnie Sahlberg <lsahlber@redhat.com>

    commit 8b6c58458ee3206dde345fce327a4cb83e69caf9 upstream.

    On umount, cifs_sb->tlink_tree might contain entries that do not represent
    a valid tcon.
    Check the tcon for error before we dereference it.

    Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
    Cc: stable@vger.kernel.org
    Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
    Reported-by: Xiaoli Feng <xifeng@redhat.com>
    Signed-off-by: Steve French <stfrench@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/cifs/cifsfs.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    --- a/fs/cifs/cifsfs.c
    +++ b/fs/cifs/cifsfs.c
    @@ -266,10 +266,11 @@ static void cifs_kill_sb(struct super_bl
    * before we kill the sb.
    */
    if (cifs_sb->root) {
    - node = rb_first(root);
    - while (node != NULL) {
    + for (node = rb_first(root); node; node = rb_next(node)) {
    tlink = rb_entry(node, struct tcon_link, tl_rbnode);
    tcon = tlink_tcon(tlink);
    + if (IS_ERR(tcon))
    + continue;
    cfid = &tcon->crfid;
    mutex_lock(&cfid->fid_mutex);
    if (cfid->dentry) {
    @@ -277,7 +278,6 @@ static void cifs_kill_sb(struct super_bl
    cfid->dentry = NULL;
    }
    mutex_unlock(&cfid->fid_mutex);
    - node = rb_next(node);
    }

    /* finally release root dentry */

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