From: Max Kellermann <max.kellermann@ionos.com>
To: to=idryomov@gmail.com,
	amarkuze@redhat.com,
	ceph-devel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Cc: Max Kellermann <max.kellermann@ionos.com>,
	stable@vger.kernel.org
Subject: [PATCH] fs/ceph: add a bunch of missing ceph_path_info initializers
Date: Tue, 24 Feb 2026 14:10:29 +0100
Message-ID: <20260224131030.3049328-1-max.kellermann@ionos.com>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

ceph_mdsc_build_path() must be called with a zero-initialized
ceph_path_info parameter, or else the following
ceph_mdsc_free_path_info() may crash.

Example crash (on Linux 6.18.12):

  virt_to_cache: Object is not a Slab page!
  WARNING: CPU: 184 PID: 2871736 at mm/slub.c:6732 kmem_cache_free+0x316/0x400
  [...]
  Call Trace:
   [...]
   ceph_open+0x13d/0x3e0
   do_dentry_open+0x134/0x480
   vfs_open+0x2a/0xe0
   path_openat+0x9a3/0x1160
  [...]
  cache_from_obj: Wrong slab cache. names_cache but object is from ceph_inode_info
  WARNING: CPU: 184 PID: 2871736 at mm/slub.c:6746 kmem_cache_free+0x2dd/0x400
  [...]
  kernel BUG at mm/slub.c:634!
  Oops: invalid opcode: 0000 [#1] SMP NOPTI
  RIP: 0010:__slab_free+0x1a4/0x350

Some of the ceph_mdsc_build_path() callers had initializers, but
others had not, even though they were all added by
commit 15f519e9f883 ("ceph: fix race condition validating r_parent
before applying state").
The ones without initializer are suspectible to random
crashes.  (I can imagine it could even be possible to exploit this bug
to elevate privileges.)

Unfortunately, these Ceph functions are undocumented and its semantics
can only be derived from the code.  I see that ceph_mdsc_build_path()
initializes the structure only on success, but not on error.

Calling ceph_mdsc_free_path_info() after a failed
ceph_mdsc_build_path() call does not even make sense, but that's what
all callers do, and for it to be safe, the structure must be
zero-initialized.  The least intrusive approach to fix this is
therefore to add initializers everywhere.

Fixes: 15f519e9f883 ("ceph: fix race condition validating r_parent before applying state")
Cc: stable@vger.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
---
 fs/ceph/debugfs.c | 4 ++--
 fs/ceph/dir.c     | 2 +-
 fs/ceph/file.c    | 4 ++--
 fs/ceph/inode.c   | 2 +-
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index f3fe786b4143..7dc307790240 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -79,7 +79,7 @@ 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) {
-			struct ceph_path_info path_info;
+			struct ceph_path_info path_info = {0};
 			path = ceph_mdsc_build_path(mdsc, req->r_dentry, &path_info, 0);
 			if (IS_ERR(path))
 				path = NULL;
@@ -98,7 +98,7 @@ static int mdsc_show(struct seq_file *s, void *p)
 		}
 
 		if (req->r_old_dentry) {
-			struct ceph_path_info path_info;
+			struct ceph_path_info path_info = {0};
 			path = ceph_mdsc_build_path(mdsc, req->r_old_dentry, &path_info, 0);
 			if (IS_ERR(path))
 				path = NULL;
diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index 86d7aa594ea9..a87c2bc09965 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -1363,7 +1363,7 @@ static int ceph_unlink(struct inode *dir, struct dentry *dentry)
 	if (!dn) {
 		try_async = false;
 	} else {
-		struct ceph_path_info path_info;
+		struct ceph_path_info path_info = {0};
 		path = ceph_mdsc_build_path(mdsc, dn, &path_info, 0);
 		if (IS_ERR(path)) {
 			try_async = false;
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 66bbf6d517a9..5e7c73a29aa3 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -397,7 +397,7 @@ int ceph_open(struct inode *inode, struct file *file)
 	if (!dentry) {
 		do_sync = true;
 	} else {
-		struct ceph_path_info path_info;
+		struct ceph_path_info path_info = {0};
 		path = ceph_mdsc_build_path(mdsc, dentry, &path_info, 0);
 		if (IS_ERR(path)) {
 			do_sync = true;
@@ -807,7 +807,7 @@ int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
 	if (!dn) {
 		try_async = false;
 	} else {
-		struct ceph_path_info path_info;
+		struct ceph_path_info path_info = {0};
 		path = ceph_mdsc_build_path(mdsc, dn, &path_info, 0);
 		if (IS_ERR(path)) {
 			try_async = false;
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index d76f9a79dc0c..d99e12d1100b 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -2551,7 +2551,7 @@ int __ceph_setattr(struct mnt_idmap *idmap, struct inode *inode,
 	if (!dentry) {
 		do_sync = true;
 	} else {
-		struct ceph_path_info path_info;
+		struct ceph_path_info path_info = {0};
 		path = ceph_mdsc_build_path(mdsc, dentry, &path_info, 0);
 		if (IS_ERR(path)) {
 			do_sync = true;
-- 
2.47.3