Message-Id: <20250804095942.2167541-2-amarkuze@redhat.com>
Date: Mon,  4 Aug 2025 09:59:41 +0000
From: Alex Markuze <amarkuze@...hat.com>
To: ceph-devel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Slava.Dubeyko@....com,
	idryomov@...il.com,
	Alex Markuze <amarkuze@...hat.com>
Subject: [PATCH v2 1/2] ceph: fix client race condition validating r_parent before applying state

Add validation to ensure the cached parent directory inode matches the
directory info in MDS replies. This prevents client-side race conditions
where concurrent operations (e.g. rename) cause r_parent to become stale
between request initiation and reply processing, which could lead to
applying state changes to incorrect directory inodes.
---
 fs/ceph/debugfs.c    |   6 +-
 fs/ceph/mds_client.c | 152 +++++++++++++++++++++++++++----------------
 fs/ceph/mds_client.h |  12 +++-
 3 files changed, 110 insertions(+), 60 deletions(-)

diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index 2ffb29108176..35e621f41039 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -88,8 +88,8 @@ static int mdsc_show(struct seq_file *s, void *p)
 		if (req->r_inode) {
 			seq_printf(s, " #%llx", ceph_ino(req->r_inode));
 		} else if (req->r_dentry) {
-			path = ceph_mdsc_build_path(mdsc, req->r_dentry, &pathlen,
-						    &pathbase, 0);
+			struct ceph_path_info path_info;
+			path = ceph_mdsc_build_path(mdsc, req->r_dentry, &path_info, 0);
 			if (IS_ERR(path))
 				path = NULL;
 			spin_lock(&req->r_dentry->d_lock);
@@ -98,7 +98,7 @@ static int mdsc_show(struct seq_file *s, void *p)
 				   req->r_dentry,
 				   path ? path : "");
 			spin_unlock(&req->r_dentry->d_lock);
-			ceph_mdsc_free_path(path, pathlen);
+			ceph_mdsc_free_path(path, path_info.pathlen);
 		} else if (req->r_path1) {
 			seq_printf(s, " #%llx/%s", req->r_ino1.ino,
 				   req->r_path1);
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 8d9fc5e18b17..d2ae862c3dda 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2732,7 +2732,7 @@ static u8 *get_fscrypt_altname(const struct ceph_mds_request *req, u32 *plen)
  *   foo/.snap/bar -> foo//bar
  */
 char *ceph_mdsc_build_path(struct ceph_mds_client *mdsc, struct dentry *dentry,
-			   int *plen, u64 *pbase, int for_wire)
+			   struct ceph_path_info *path_info, int for_wire)
 {
 	struct ceph_client *cl = mdsc->fsc->client;
 	struct dentry *cur;
@@ -2843,17 +2843,31 @@ char *ceph_mdsc_build_path(struct ceph_mds_client *mdsc, struct dentry *dentry,
 		return ERR_PTR(-ENAMETOOLONG);
 	}
 
-	*pbase = base;
-	*plen = PATH_MAX - 1 - pos;
-	CEPH_SAN_STRNCPY(result_str, sizeof(result_str), path + pos, *plen);
+	/* Initialize the output structure */
+	memset(path_info, 0, sizeof(*path_info));
+
+	path_info->vino.ino = base;
+	path_info->pathlen = PATH_MAX - 1 - pos;
+	path_info->path = path + pos;
+	path_info->freepath = true;
+
+	/* Set snap from dentry if available */
+	if (d_inode(dentry))
+		path_info->vino.snap = ceph_snap(d_inode(dentry));
+	else
+		path_info->vino.snap = CEPH_NOSNAP;
+
+	CEPH_SAN_STRNCPY(result_str, sizeof(result_str), path_info->path, path_info->pathlen);
 	boutc(cl, "on %p %d built %llx '%s'\n", dentry, d_count(dentry),
-	      base, result_str);
+	      path_info->vino.ino, result_str);
 	return path + pos;
 }
 
+
+
 static int build_dentry_path(struct ceph_mds_client *mdsc, struct dentry *dentry,
-			     struct inode *dir, const char **ppath, int *ppathlen,
-			     u64 *pino, bool *pfreepath, bool parent_locked)
+			     struct inode *dir, struct ceph_path_info *path_info,
+			     bool parent_locked)
 {
 	char *path;
 
@@ -2862,41 +2876,47 @@ static int build_dentry_path(struct ceph_mds_client *mdsc, struct dentry *dentry
 		dir = d_inode_rcu(dentry->d_parent);
 	if (dir && parent_locked && ceph_snap(dir) == CEPH_NOSNAP &&
 	    !IS_ENCRYPTED(dir)) {
-		*pino = ceph_ino(dir);
+		path_info->vino.ino = ceph_ino(dir);
+		path_info->vino.snap = ceph_snap(dir);
 		rcu_read_unlock();
-		*ppath = dentry->d_name.name;
-		*ppathlen = dentry->d_name.len;
+		path_info->path = dentry->d_name.name;
+		path_info->pathlen = dentry->d_name.len;
+		path_info->freepath = false;
 		return 0;
 	}
 	rcu_read_unlock();
-	path = ceph_mdsc_build_path(mdsc, dentry, ppathlen, pino, 1);
+	path = ceph_mdsc_build_path(mdsc, dentry, path_info, 1);
 	if (IS_ERR(path))
 		return PTR_ERR(path);
-	*ppath = path;
-	*pfreepath = true;
+	/*
+	 * ceph_mdsc_build_path already fills path_info, including snap handling.
+	 */
 	return 0;
 }
 
-static int build_inode_path(struct inode *inode,
-			    const char **ppath, int *ppathlen, u64 *pino,
-			    bool *pfreepath)
+static int build_inode_path(struct inode *inode, struct ceph_path_info *path_info)
 {
 	struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(inode->i_sb);
 	struct dentry *dentry;
 	char *path;
 
 	if (ceph_snap(inode) == CEPH_NOSNAP) {
-		*pino = ceph_ino(inode);
-		*ppathlen = 0;
+		path_info->vino.ino = ceph_ino(inode);
+		path_info->vino.snap = ceph_snap(inode);
+		path_info->pathlen = 0;
+		path_info->freepath = false;
 		return 0;
 	}
 	dentry = d_find_alias(inode);
-	path = ceph_mdsc_build_path(mdsc, dentry, ppathlen, pino, 1);
+	path = ceph_mdsc_build_path(mdsc, dentry, path_info, 1);
 	dput(dentry);
 	if (IS_ERR(path))
 		return PTR_ERR(path);
-	*ppath = path;
-	*pfreepath = true;
+	/*
+	 * ceph_mdsc_build_path already fills path_info, including snap from dentry.
+	 * Override with inode's snap since that's what this function is for.
+	 */
+	path_info->vino.snap = ceph_snap(inode);
 	return 0;
 }
 
@@ -2906,28 +2926,31 @@ static int build_inode_path(struct inode *inode,
  */
 static int set_request_path_attr(struct ceph_mds_client *mdsc, struct inode *rinode,
 				 struct dentry *rdentry, struct inode *rdiri,
-				 const char *rpath, u64 rino, const char **ppath,
-				 int *pathlen, u64 *ino, bool *freepath,
+				 const char *rpath, u64 rino, struct ceph_path_info *path_info,
 				 bool parent_locked)
 {
 	struct ceph_client *cl = mdsc->fsc->client;
 	char result_str[128];
 	int r = 0;
 
+	/* Initialize the output structure */
+	memset(path_info, 0, sizeof(*path_info));
+
 	if (rinode) {
-		r = build_inode_path(rinode, ppath, pathlen, ino, freepath);
+		r = build_inode_path(rinode, path_info);
 		boutc(cl, " inode %p %llx.%llx\n", rinode, ceph_ino(rinode),
-		      ceph_snap(rinode));
+		ceph_snap(rinode));
 	} else if (rdentry) {
-		r = build_dentry_path(mdsc, rdentry, rdiri, ppath, pathlen, ino,
-					freepath, parent_locked);
-		CEPH_SAN_STRNCPY(result_str, sizeof(result_str), *ppath, *pathlen);
-		boutc(cl, " dentry %p %llx/%s\n", rdentry, *ino, result_str);
+		r = build_dentry_path(mdsc, rdentry, rdiri, path_info, parent_locked);
+		CEPH_SAN_STRNCPY(result_str, sizeof(result_str), path_info->path, path_info->pathlen);
+		boutc(cl, " dentry %p %llx/%s\n", rdentry, path_info->vino.ino, result_str);
 	} else if (rpath || rino) {
-		*ino = rino;
-		*ppath = rpath;
-		*pathlen = rpath ? strlen(rpath) : 0;
-		CEPH_SAN_STRNCPY(result_str, sizeof(result_str), rpath, *pathlen);
+		path_info->vino.ino = rino;
+		path_info->vino.snap = CEPH_NOSNAP;
+		path_info->path = rpath;
+		path_info->pathlen = rpath ? strlen(rpath) : 0;
+		path_info->freepath = false;
+		CEPH_SAN_STRNCPY(result_str, sizeof(result_str), rpath, path_info->pathlen);
 		boutc(cl," path %s\n", result_str);
 	}
 
@@ -3005,11 +3028,8 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 	struct ceph_client *cl = mdsc->fsc->client;
 	struct ceph_msg *msg;
 	struct ceph_mds_request_head_legacy *lhead;
-	const char *path1 = NULL;
-	const char *path2 = NULL;
-	u64 ino1 = 0, ino2 = 0;
-	int pathlen1 = 0, pathlen2 = 0;
-	bool freepath1 = false, freepath2 = false;
+	struct ceph_path_info path_info1 = {0};
+	struct ceph_path_info path_info2 = {0};
 	struct dentry *old_dentry = NULL;
 	int len;
 	u16 releases;
@@ -3019,25 +3039,42 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 	u16 request_head_version = mds_supported_head_version(session);
 	kuid_t caller_fsuid = req->r_cred->fsuid;
 	kgid_t caller_fsgid = req->r_cred->fsgid;
+	bool parent_locked = test_bit(CEPH_MDS_R_PARENT_LOCKED, &req->r_req_flags);
 
-	ret = set_request_path_attr(mdsc, req->r_inode, req->r_dentry,
-			      req->r_parent, req->r_path1, req->r_ino1.ino,
-			      &path1, &pathlen1, &ino1, &freepath1,
-			      test_bit(CEPH_MDS_R_PARENT_LOCKED,
-					&req->r_req_flags));
+		ret = set_request_path_attr(mdsc, req->r_inode, req->r_dentry,
+		      req->r_parent, req->r_path1, req->r_ino1.ino,
+		      &path_info1, parent_locked);
 	if (ret < 0) {
 		msg = ERR_PTR(ret);
 		goto out;
 	}
 
+	/*
+	 * When the parent directory's i_rwsem is *not* locked, req->r_parent may
+	 * have become stale (e.g. after a concurrent rename) between the time the
+	 * dentry was looked up and now.  If we detect that the stored r_parent
+	 * does not match the inode number we just encoded for the request, switch
+	 * to the correct inode so that the MDS receives a valid parent reference.
+	 */
+	if (!parent_locked &&
+	    	req->r_parent && path_info1.vino.ino && ceph_ino(req->r_parent) != path_info1.vino.ino) {
+		struct inode *correct_dir = ceph_get_inode(mdsc->fsc->sb, path_info1.vino, NULL);
+		if (!IS_ERR(correct_dir)) {
+			WARN(1, "ceph: r_parent mismatch (had %llx wanted %llx) - updating\n",
+			     ceph_ino(req->r_parent), path_info1.vino.ino);
+			iput(req->r_parent);
+			req->r_parent = correct_dir;
+		}
+	}
+
 	/* If r_old_dentry is set, then assume that its parent is locked */
 	if (req->r_old_dentry &&
 	    !(req->r_old_dentry->d_flags & DCACHE_DISCONNECTED))
 		old_dentry = req->r_old_dentry;
 	ret = set_request_path_attr(mdsc, NULL, old_dentry,
-			      req->r_old_dentry_dir,
-			      req->r_path2, req->r_ino2.ino,
-			      &path2, &pathlen2, &ino2, &freepath2, true);
+		      req->r_old_dentry_dir,
+		      req->r_path2, req->r_ino2.ino,
+		      &path_info2, true);
 	if (ret < 0) {
 		msg = ERR_PTR(ret);
 		goto out_free1;
@@ -3068,7 +3105,7 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 
 	/* filepaths */
 	len += 2 * (1 + sizeof(u32) + sizeof(u64));
-	len += pathlen1 + pathlen2;
+	len += path_info1.pathlen + path_info2.pathlen;
 
 	/* cap releases */
 	len += sizeof(struct ceph_mds_request_release) *
@@ -3076,9 +3113,9 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 		 !!req->r_old_inode_drop + !!req->r_old_dentry_drop);
 
 	if (req->r_dentry_drop)
-		len += pathlen1;
+		len += path_info1.pathlen;
 	if (req->r_old_dentry_drop)
-		len += pathlen2;
+		len += path_info2.pathlen;
 
 	/* MClientRequest tail */
 
@@ -3191,8 +3228,8 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 	lhead->ino = cpu_to_le64(req->r_deleg_ino);
 	lhead->args = req->r_args;
 
-	ceph_encode_filepath(&p, end, ino1, path1);
-	ceph_encode_filepath(&p, end, ino2, path2);
+	ceph_encode_filepath(&p, end, path_info1.vino.ino, path_info1.path);
+	ceph_encode_filepath(&p, end, path_info2.vino.ino, path_info2.path);
 
 	/* make note of release offset, in case we need to replay */
 	req->r_request_release_offset = p - msg->front.iov_base;
@@ -3255,11 +3292,11 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 	msg->hdr.data_off = cpu_to_le16(0);
 
 out_free2:
-	if (freepath2)
-		ceph_mdsc_free_path((char *)path2, pathlen2);
+	if (path_info2.freepath)
+		ceph_mdsc_free_path((char *)path_info2.path, path_info2.pathlen);
 out_free1:
-	if (freepath1)
-		ceph_mdsc_free_path((char *)path1, pathlen1);
+	if (path_info1.freepath)
+		ceph_mdsc_free_path((char *)path_info1.path, path_info1.pathlen);
 out:
 	return msg;
 out_err:
@@ -4623,14 +4660,17 @@ static int reconnect_caps_cb(struct inode *inode, int mds, void *arg)
 
 	dentry = d_find_primary(inode);
 	if (dentry) {
+		struct ceph_path_info path_info;
 		/* set pathbase to parent dir when msg_version >= 2 */
-		path = ceph_mdsc_build_path(mdsc, dentry, &pathlen, &pathbase,
+		path = ceph_mdsc_build_path(mdsc, dentry, &path_info,
 					    recon_state->msg_version >= 2);
 		dput(dentry);
 		if (IS_ERR(path)) {
 			err = PTR_ERR(path);
 			goto out_err;
 		}
+		pathlen = path_info.pathlen;
+		pathbase = path_info.vino.ino;
 	} else {
 		path = NULL;
 		pathbase = 0;
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 3e2a6fa7c19a..c4c1ea8d5f5e 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -623,8 +623,18 @@ static inline void ceph_mdsc_free_path(char *path, int len)
 		__putname(path - (PATH_MAX - 1 - len));
 }
 
+/*
+ * Structure to group path-related output parameters for build_*_path functions
+ */
+struct ceph_path_info {
+	const char *path;
+	int pathlen;
+	struct ceph_vino vino;
+	bool freepath;
+};
+
 extern char *ceph_mdsc_build_path(struct ceph_mds_client *mdsc,
-				  struct dentry *dentry, int *plen, u64 *base,
+				  struct dentry *dentry, struct ceph_path_info *path_info,
 				  int for_wire);
 
 extern void __ceph_mdsc_drop_dentry_lease(struct dentry *dentry);
-- 
2.34.1

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