[PATCH v3] ceph: fix NULL pointer dereference for req->r_session

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From: Xiubo Li <xiubli@xxxxxxxxxx>

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

Cc: stable@xxxxxxxxxxxxxxx
URL: https://bugzilla.redhat.com/show_bug.cgi?id=2137955
Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
---
 fs/ceph/caps.c | 60 ++++++++++++++++----------------------------------
 1 file changed, 19 insertions(+), 41 deletions(-)

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 894adfb4a092..83f9e18e3169 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -2297,8 +2297,10 @@ 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;
+	struct ceph_mds_session **sessions = NULL;
+	struct ceph_mds_session *s;
 	unsigned int max_sessions;
-	int ret, err = 0;
+	int i, ret, err = 0;
 
 	spin_lock(&ci->i_unsafe_lock);
 	if (S_ISDIR(inode->i_mode) && !list_empty(&ci->i_unsafe_dirops)) {
@@ -2315,28 +2317,19 @@ 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;
+	mutex_lock(&mdsc->mutex);
+	max_sessions = mdsc->max_sessions;
+	if (req1 || req2) {
 		struct ceph_mds_request *req;
-		int i;
 
 		sessions = kcalloc(max_sessions, sizeof(s), GFP_KERNEL);
 		if (!sessions) {
+			mutex_unlock(&mdsc->mutex);
 			err = -ENOMEM;
 			goto out;
 		}
@@ -2346,18 +2339,8 @@ 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))
 					continue;
-				if (unlikely(s->s_mds >= max_sessions)) {
-					spin_unlock(&ci->i_unsafe_lock);
-					for (i = 0; i < max_sessions; i++) {
-						s = sessions[i];
-						if (s)
-							ceph_put_mds_session(s);
-					}
-					kfree(sessions);
-					goto retry;
-				}
 				if (!sessions[s->s_mds]) {
 					s = ceph_get_mds_session(s);
 					sessions[s->s_mds] = s;
@@ -2368,18 +2351,8 @@ static int flush_mdlog_and_wait_inode_unsafe_requests(struct inode *inode)
 			list_for_each_entry(req, &ci->i_unsafe_iops,
 					    r_unsafe_target_item) {
 				s = req->r_session;
-				if (!s)
+				if (!s || unlikely(s->s_mds >= max_sessions))
 					continue;
-				if (unlikely(s->s_mds >= max_sessions)) {
-					spin_unlock(&ci->i_unsafe_lock);
-					for (i = 0; i < max_sessions; i++) {
-						s = sessions[i];
-						if (s)
-							ceph_put_mds_session(s);
-					}
-					kfree(sessions);
-					goto retry;
-				}
 				if (!sessions[s->s_mds]) {
 					s = ceph_get_mds_session(s);
 					sessions[s->s_mds] = s;
@@ -2391,13 +2364,18 @@ static int flush_mdlog_and_wait_inode_unsafe_requests(struct inode *inode)
 		/* the auth MDS */
 		spin_lock(&ci->i_ceph_lock);
 		if (ci->i_auth_cap) {
-		      s = ci->i_auth_cap->session;
-		      if (!sessions[s->s_mds])
-			      sessions[s->s_mds] = ceph_get_mds_session(s);
+			s = ci->i_auth_cap->session;
+			if (likely(s->s_mds < max_sessions)
+			    && !sessions[s->s_mds]) {
+				sessions[s->s_mds] = ceph_get_mds_session(s);
+			}
 		}
 		spin_unlock(&ci->i_ceph_lock);
+	}
+	mutex_unlock(&mdsc->mutex);
 
-		/* send flush mdlog request to MDSes */
+	/* send flush mdlog request to MDSes */
+	if (sessions) {
 		for (i = 0; i < max_sessions; i++) {
 			s = sessions[i];
 			if (s) {
@@ -2405,7 +2383,6 @@ static int flush_mdlog_and_wait_inode_unsafe_requests(struct inode *inode)
 				ceph_put_mds_session(s);
 			}
 		}
-		kfree(sessions);
 	}
 
 	dout("%s %p wait on tid %llu %llu\n", __func__,
@@ -2424,6 +2401,7 @@ static int flush_mdlog_and_wait_inode_unsafe_requests(struct inode *inode)
 	}
 
 out:
+	kfree(sessions);
 	if (req1)
 		ceph_mdsc_put_request(req1);
 	if (req2)
-- 
2.31.1




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