Re: [PATCH v4] ceph: fix NULL pointer dereference for req->r_session

On Thu, Nov 10, 2022 at 3:08 AM xiubli@redhat.com wrote:

From: Xiubo Li xiubli@redhat.com

The request's r_session maybe changed when it was forwarded or resent.

Cc: stable@vger.kernel.org URL: https://bugzilla.redhat.com/show_bug.cgi?id=2137955 Signed-off-by: Xiubo Li xiubli@redhat.com

---

Changed in V4:

• move mdsc->mutex acquisition and max_sessions assignment into "if (req1 || req2)" branch

fs/ceph/caps.c | 54 +++++++++++++++----------------------------------- 1 file changed, 16 insertions(+), 38 deletions(-)

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c index 894adfb4a092..1c84be839087 100644 --- a/fs/ceph/caps.c +++ b/fs/ceph/caps.c @@ -2297,7 +2297,6 @@ static int flush_mdlog_and_wait_inode_unsafe_requests(struct inode *inode) struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc; struct ceph_inode_info *ci = ceph_inode(inode); struct ceph_mds_request *req1 = NULL, *req2 = NULL;

•   unsigned int max_sessions;
    int ret, err = 0;
  
    spin_lock(&ci->i_unsafe_lock);
  

@@ -2315,28 +2314,24 @@ static int flush_mdlog_and_wait_inode_unsafe_requests(struct inode *inode) } spin_unlock(&ci->i_unsafe_lock);

•   /*
  

•    * The mdsc->max_sessions is unlikely to be changed
  

•    * mostly, here we will retry it by reallocating the
  

•    * sessions array memory to get rid of the mdsc->mutex
  

•    * lock.
  

•    */
  

-retry:

•   max_sessions = mdsc->max_sessions;
  

•   /*
     * Trigger to flush the journal logs in all the relevant MDSes
     * manually, or in the worst case we must wait at most 5 seconds
     * to wait the journal logs to be flushed by the MDSes periodically.
     */
  

•   if ((req1 || req2) && likely(max_sessions)) {
  

•           struct ceph_mds_session **sessions = NULL;
  

•           struct ceph_mds_session *s;
  

•   if (req1 || req2) {
            struct ceph_mds_request *req;
  

•           struct ceph_mds_session **sessions;
  

•           struct ceph_mds_session *s;
  

•           unsigned int max_sessions;
            int i;
  
  

•           mutex_lock(&mdsc->mutex);
  

•           max_sessions = mdsc->max_sessions;
  

•           sessions = kcalloc(max_sessions, sizeof(s), GFP_KERNEL);
            if (!sessions) {
  

•                   mutex_unlock(&mdsc->mutex);
                    err = -ENOMEM;
                    goto out;
            }
  

@@ -2346,18 +2341,8 @@ static int flush_mdlog_and_wait_inode_unsafe_requests(struct inode *inode) list_for_each_entry(req, &ci->i_unsafe_dirops, r_unsafe_dir_item) { s = req->r_session;

•                           if (!s)
  

•                           if (!s || unlikely(s->s_mds >= max_sessions))
  

Hi Xiubo,

I would be fine with this patch as is but I'm wondering if it can be simplified further. Now that mdsc->mutex is held while sessions array is populated, is checking s->s_mds against max_sessions actually needed? Is it possible for some req->r_session on one of the unsafe lists to have an "out of bounds" s_mds under mdsc->mutex?

Thanks,

Ilya