[PATCH v2 stable/linux-6.6.y 0/3] Backport Fix incorrect overlayfs mmap() and mprotect() LSM access controls

[PATCH v2 stable/linux-6.6.y 0/3] Backport Fix incorrect overlayfs mmap() and mprotect() LSM access controls

[Cai Xinchen]

v2: Add static to struct kmem_cache *lsm_backing_file_cache; and define
lbs_backing_file as int for keeping the same type as 6.6 lts. Use macro
backing_file to replace inline function to eliminate the const warning.

Backport the patch series
"Fix incorrect overlayfs mmap() and mprotect() LSM access controls" [1]
to 6.6 lts

I test selinux-testsuite[2] overlay test, it pass 135 tests.

[1] https://lore.kernel.org/all/20260403030848.731867-5-paul@paul-moore.com/
[2] https://github.com/SELinuxProject/selinux-testsuite

Amir Goldstein (1):
  fs: prepare for adding LSM blob to backing_file

Paul Moore (2):
  lsm: add backing_file LSM hooks
  selinux: fix overlayfs mmap() and mprotect() access checks

 fs/file_table.c                   |  46 +++++-
 fs/internal.h                     |   3 +-
 fs/open.c                         |   7 +-
 fs/overlayfs/file.c               |   8 +-
 include/linux/fs.h                |  15 +-
 include/linux/lsm_audit.h         |   2 +-
 include/linux/lsm_hook_defs.h     |   5 +
 include/linux/lsm_hooks.h         |   1 +
 include/linux/security.h          |  22 +++
 security/security.c               | 110 ++++++++++++++
 security/selinux/hooks.c          | 242 ++++++++++++++++++++++--------
 security/selinux/include/objsec.h |  11 ++
 12 files changed, 395 insertions(+), 77 deletions(-)

-- 
2.18.0.huawei.25

[PATCH v2 stable/linux-6.6.y 1/3] fs: prepare for adding LSM blob to backing_file

[Cai Xinchen]

From: Amir Goldstein <amir73il@gmail.com>

[ Upstream commit 880bd496ec72a6dcb00cb70c430ef752ba242ae7 ]

In preparation to adding LSM blob to backing_file struct, factor out
helpers init_backing_file() and backing_file_free().

Cc: stable@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-unionfs@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
[PM: use the term "LSM blob", fix comment style to match file]
Signed-off-by: Paul Moore <paul@paul-moore.com>
[1. The commit def3ae83da02
("fs: store real path instead of fake path in backing file f_path")
is not merged, The 6.6 LTS version accordingly operates on
&ff->real_path instead of &ff->user_path.

2. Mainline's file_free() does both the backing_file cleanup and the
kmem_cache_free() synchronously.  Linux 6.6.y defers the actual kfree()
to file_free_rcu() via call_rcu(), so only path_put() is done
synchronously in file_free().]
Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>
---
 fs/file_table.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 234284ef72a9..b4c208a77153 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -72,11 +72,16 @@ static void file_free_rcu(struct rcu_head *head)
 		kmem_cache_free(filp_cachep, f);
 }
 
+static inline void backing_file_free(struct backing_file *ff)
+{
+	path_put(&ff->real_path);
+}
+
 static inline void file_free(struct file *f)
 {
 	security_file_free(f);
 	if (unlikely(f->f_mode & FMODE_BACKING))
-		path_put(backing_file_real_path(f));
+		backing_file_free(backing_file(f));
 	if (likely(!(f->f_mode & FMODE_NOACCOUNT)))
 		percpu_counter_dec(&nr_files);
 	call_rcu(&f->f_rcuhead, file_free_rcu);
@@ -252,6 +257,12 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
 	return f;
 }
 
+static int init_backing_file(struct backing_file *ff)
+{
+	memset(&ff->real_path, 0, sizeof(ff->real_path));
+	return 0;
+}
+
 /*
  * Variant of alloc_empty_file() that allocates a backing_file container
  * and doesn't check and modify nr_files.
@@ -274,7 +285,14 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
 		return ERR_PTR(error);
 	}
 
+	/* The f_mode flags must be set before fput(). */
 	ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT;
+	error = init_backing_file(ff);
+	if (unlikely(error)) {
+		fput(&ff->file);
+		return ERR_PTR(error);
+	}
+
 	return &ff->file;
 }
 
-- 
2.18.0.huawei.25

Re: [PATCH v2 stable/linux-6.6.y 1/3] fs: prepare for adding LSM blob to backing_file

[sashiko-bot]

> From: Amir Goldstein <amir73il@gmail.com>
> 
> [ Upstream commit 880bd496ec72a6dcb00cb70c430ef752ba242ae7 ]
> 
> In preparation to adding LSM blob to backing_file struct, factor out
> helpers init_backing_file() and backing_file_free().
> 
> Cc: stable@vger.kernel.org
> Cc: linux-fsdevel@vger.kernel.org
> Cc: linux-unionfs@vger.kernel.org
> Cc: linux-erofs@lists.ozlabs.org
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> Reviewed-by: Serge Hallyn <serge@hallyn.com>
> [PM: use the term "LSM blob", fix comment style to match file]
> Signed-off-by: Paul Moore <paul@paul-moore.com>
> [1. The commit def3ae83da02
> ("fs: store real path instead of fake path in backing file f_path")
> is not merged, The 6.6 LTS version accordingly operates on
> &ff->real_path instead of &ff->user_path.
> 
> 2. Mainline's file_free() does both the backing_file cleanup and the
> kmem_cache_free() synchronously.  Linux 6.6.y defers the actual kfree()
> to file_free_rcu() via call_rcu(), so only path_put() is done
> synchronously in file_free().]
> Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260627065720.1945589-1-caixinchen1@huawei.com?part=1

[PATCH v2 stable/linux-6.6.y 2/3] lsm: add backing_file LSM hooks

[Cai Xinchen]

From: Paul Moore <paul@paul-moore.com>

[ Upstream commit 6af36aeb147a06dea47c49859cd6ca5659aeb987 ]

Stacked filesystems such as overlayfs do not currently provide the
necessary mechanisms for LSMs to properly enforce access controls on the
mmap() and mprotect() operations.  In order to resolve this gap, a LSM
security blob is being added to the backing_file struct and the following
new LSM hooks are being created:

 security_backing_file_alloc()
 security_backing_file_free()
 security_mmap_backing_file()

The first two hooks are to manage the lifecycle of the LSM security blob
in the backing_file struct, while the third provides a new mmap() access
control point for the underlying backing file.  It is also expected that
LSMs will likely want to update their security_file_mprotect() callback
to address issues with their mprotect() controls, but that does not
require a change to the security_file_mprotect() LSM hook.

There are a three other small changes to support these new LSM hooks:
* Pass the user file associated with a backing file down to
alloc_empty_backing_file() so it can be included in the
security_backing_file_alloc() hook.
* Add getter and setter functions for the backing_file struct LSM blob
as the backing_file struct remains private to fs/file_table.c.
* Constify the file struct field in the LSM common_audit_data struct to
better support LSMs that need to pass a const file struct pointer into
the common LSM audit code.

Thanks to Arnd Bergmann for identifying the missing EXPORT_SYMBOL_GPL()
and supplying a fixup.

Cc: stable@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-unionfs@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>
[1. Mainline uses call_int_hook(FUNC, ...) with the default IRC baked
into the macro. Linux 6.6.y uses call_int_hook(FUNC, IRC, ...) requiring
an explicit default return value.

2. fs/backing-file.c does not exist in LTS
Linux 6.6.y places backing_file_open() in fs/open.c and lacks a
dedicated fs/backing-file.c.  The backing_file_mmap() function and
scoped_with_creds() do not exist in 6.6.y.  Therefore the LTS patch calls
security_mmap_backing_file() directly in ovl_mmap() in
fs/overlayfs/file.c rather than modifying backing_file_mmap().

3. Missing filesystems/modules
Linux 6.6.y does not have backing_tmpfile_open(), fs/fuse/passthrough.c,
or the erofs ishare mmap path that the mainline patch touches.  These hunks
are dropped in the 6.6 LTS backport.

4. Use macro backing_file to replace inline function to eliminate the
const warning.]
Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>
---
 fs/file_table.c               |  32 +++++++---
 fs/internal.h                 |   3 +-
 fs/open.c                     |   7 ++-
 fs/overlayfs/file.c           |   8 ++-
 include/linux/fs.h            |  15 ++++-
 include/linux/lsm_audit.h     |   2 +-
 include/linux/lsm_hook_defs.h |   5 ++
 include/linux/lsm_hooks.h     |   1 +
 include/linux/security.h      |  22 +++++++
 security/security.c           | 110 ++++++++++++++++++++++++++++++++++
 10 files changed, 190 insertions(+), 15 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index b4c208a77153..fa4d4c54f790 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -48,12 +48,12 @@ static struct percpu_counter nr_files __cacheline_aligned_in_smp;
 struct backing_file {
 	struct file file;
 	struct path real_path;
+#ifdef CONFIG_SECURITY
+	void *security;
+#endif
 };
 
-static inline struct backing_file *backing_file(struct file *f)
-{
-	return container_of(f, struct backing_file, file);
-}
+#define backing_file(f) container_of(f, struct backing_file, file)
 
 struct path *backing_file_real_path(struct file *f)
 {
@@ -72,8 +72,21 @@ static void file_free_rcu(struct rcu_head *head)
 		kmem_cache_free(filp_cachep, f);
 }
 
+#ifdef CONFIG_SECURITY
+void *backing_file_security(const struct file *f)
+{
+	return backing_file(f)->security;
+}
+
+void backing_file_set_security(struct file *f, void *security)
+{
+	backing_file(f)->security = security;
+}
+#endif /* CONFIG_SECURITY */
+
 static inline void backing_file_free(struct backing_file *ff)
 {
+	security_backing_file_free(&ff->file);
 	path_put(&ff->real_path);
 }
 
@@ -257,10 +270,12 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
 	return f;
 }
 
-static int init_backing_file(struct backing_file *ff)
+static int init_backing_file(struct backing_file *ff,
+			     const struct file *user_file)
 {
 	memset(&ff->real_path, 0, sizeof(ff->real_path));
-	return 0;
+	backing_file_set_security(&ff->file, NULL);
+	return security_backing_file_alloc(&ff->file, user_file);
 }
 
 /*
@@ -270,7 +285,8 @@ static int init_backing_file(struct backing_file *ff)
  * This is only for kernel internal use, and the allocate file must not be
  * installed into file tables or such.
  */
-struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
+struct file *alloc_empty_backing_file(int flags, const struct cred *cred,
+				      const struct file *user_file)
 {
 	struct backing_file *ff;
 	int error;
@@ -287,7 +303,7 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
 
 	/* The f_mode flags must be set before fput(). */
 	ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT;
-	error = init_backing_file(ff);
+	error = init_backing_file(ff, user_file);
 	if (unlikely(error)) {
 		fput(&ff->file);
 		return ERR_PTR(error);
diff --git a/fs/internal.h b/fs/internal.h
index d64ae03998cc..576026e1ce3a 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -93,7 +93,8 @@ extern void chroot_fs_refs(const struct path *, const struct path *);
  */
 struct file *alloc_empty_file(int flags, const struct cred *cred);
 struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred);
-struct file *alloc_empty_backing_file(int flags, const struct cred *cred);
+struct file *alloc_empty_backing_file(int flags, const struct cred *cred,
+				      const struct file *user_file);
 
 static inline void put_file_access(struct file *file)
 {
diff --git a/fs/open.c b/fs/open.c
index b5ea1dcbfb22..5b164481d80b 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1175,18 +1175,19 @@ EXPORT_SYMBOL_GPL(kernel_file_open);
  * the backing inode on the underlying filesystem, which can be
  * retrieved using backing_file_real_path().
  */
-struct file *backing_file_open(const struct path *path, int flags,
+struct file *backing_file_open(const struct file *user_file, int flags,
 			       const struct path *real_path,
 			       const struct cred *cred)
 {
+	const struct path *user_path = &user_file->f_path;
 	struct file *f;
 	int error;
 
-	f = alloc_empty_backing_file(flags, cred);
+	f = alloc_empty_backing_file(flags, cred, user_file);
 	if (IS_ERR(f))
 		return f;
 
-	f->f_path = *path;
+	f->f_path = *user_path;
 	path_get(real_path);
 	*backing_file_real_path(f) = *real_path;
 	error = do_dentry_open(f, d_inode(real_path->dentry), NULL);
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 8be4dc050d1e..07f00cf91977 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -60,7 +60,7 @@ static struct file *ovl_open_realfile(const struct file *file,
 		if (!inode_owner_or_capable(real_idmap, realinode))
 			flags &= ~O_NOATIME;
 
-		realfile = backing_file_open(&file->f_path, flags, realpath,
+		realfile = backing_file_open(file, flags, realpath,
 					     current_cred());
 	}
 	revert_creds(old_cred);
@@ -527,6 +527,7 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 
 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 {
+	struct file *user_file = vma->vm_file;
 	struct file *realfile = file->private_data;
 	const struct cred *old_cred;
 	int ret;
@@ -540,6 +541,11 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 	vma_set_file(vma, realfile);
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
+	ret = security_mmap_backing_file(vma, realfile, user_file);
+	if (ret) {
+		revert_creds(old_cred);
+		return ret;
+	}
 	ret = call_mmap(vma->vm_file, vma);
 	revert_creds(old_cred);
 	ovl_file_accessed(file);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4cdeeaedaa40..5a897ee50f29 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2515,11 +2515,24 @@ struct file *dentry_open(const struct path *path, int flags,
 			 const struct cred *creds);
 struct file *dentry_create(const struct path *path, int flags, umode_t mode,
 			   const struct cred *cred);
-struct file *backing_file_open(const struct path *path, int flags,
+struct file *backing_file_open(const struct file *user_file, int flags,
 			       const struct path *real_path,
 			       const struct cred *cred);
 struct path *backing_file_real_path(struct file *f);
 
+#ifdef CONFIG_SECURITY
+void *backing_file_security(const struct file *f);
+void backing_file_set_security(struct file *f, void *security);
+#else
+static inline void *backing_file_security(const struct file *f)
+{
+	return NULL;
+}
+static inline void backing_file_set_security(struct file *f, void *security)
+{
+}
+#endif /* CONFIG_SECURITY */
+
 /*
  * file_real_path - get the path corresponding to f_inode
  *
diff --git a/include/linux/lsm_audit.h b/include/linux/lsm_audit.h
index 97a8b21eb033..c0a2839253fa 100644
--- a/include/linux/lsm_audit.h
+++ b/include/linux/lsm_audit.h
@@ -93,7 +93,7 @@ struct common_audit_data {
 #endif
 		char *kmod_name;
 		struct lsm_ioctlop_audit *op;
-		struct file *file;
+		const struct file *file;
 		struct lsm_ibpkey_audit *ibpkey;
 		struct lsm_ibendport_audit *ibendport;
 		int reason;
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 2923754c13bc..567d7f16609c 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -169,6 +169,9 @@ LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,
 LSM_HOOK(int, 0, file_permission, struct file *file, int mask)
 LSM_HOOK(int, 0, file_alloc_security, struct file *file)
 LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file)
+LSM_HOOK(int, 0, backing_file_alloc, struct file *backing_file,
+	 const struct file *user_file)
+LSM_HOOK(void, LSM_RET_VOID, backing_file_free, struct file *backing_file)
 LSM_HOOK(int, 0, file_ioctl, struct file *file, unsigned int cmd,
 	 unsigned long arg)
 LSM_HOOK(int, 0, file_ioctl_compat, struct file *file, unsigned int cmd,
@@ -176,6 +179,8 @@ LSM_HOOK(int, 0, file_ioctl_compat, struct file *file, unsigned int cmd,
 LSM_HOOK(int, 0, mmap_addr, unsigned long addr)
 LSM_HOOK(int, 0, mmap_file, struct file *file, unsigned long reqprot,
 	 unsigned long prot, unsigned long flags)
+LSM_HOOK(int, 0, mmap_backing_file, struct vm_area_struct *vma,
+	 struct file *backing_file, struct file *user_file)
 LSM_HOOK(int, 0, file_mprotect, struct vm_area_struct *vma,
 	 unsigned long reqprot, unsigned long prot)
 LSM_HOOK(int, 0, file_lock, struct file *file, unsigned int cmd)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index dcb5e5b5eb13..3b56b60195ce 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -59,6 +59,7 @@ struct security_hook_list {
 struct lsm_blob_sizes {
 	int	lbs_cred;
 	int	lbs_file;
+	int lbs_backing_file;
 	int	lbs_inode;
 	int	lbs_superblock;
 	int	lbs_ipc;
diff --git a/include/linux/security.h b/include/linux/security.h
index 937840870d86..4866ffdb4e6c 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -389,11 +389,17 @@ int security_kernfs_init_security(struct kernfs_node *kn_dir,
 int security_file_permission(struct file *file, int mask);
 int security_file_alloc(struct file *file);
 void security_file_free(struct file *file);
+int security_backing_file_alloc(struct file *backing_file,
+				const struct file *user_file);
+void security_backing_file_free(struct file *backing_file);
 int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 int security_file_ioctl_compat(struct file *file, unsigned int cmd,
 			       unsigned long arg);
 int security_mmap_file(struct file *file, unsigned long prot,
 			unsigned long flags);
+int security_mmap_backing_file(struct vm_area_struct *vma,
+			       struct file *backing_file,
+			       struct file *user_file);
 int security_mmap_addr(unsigned long addr);
 int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
 			   unsigned long prot);
@@ -984,6 +990,15 @@ static inline int security_file_alloc(struct file *file)
 static inline void security_file_free(struct file *file)
 { }
 
+static inline int security_backing_file_alloc(struct file *backing_file,
+					      const struct file *user_file)
+{
+	return 0;
+}
+
+static inline void security_backing_file_free(struct file *backing_file)
+{ }
+
 static inline int security_file_ioctl(struct file *file, unsigned int cmd,
 				      unsigned long arg)
 {
@@ -1003,6 +1018,13 @@ static inline int security_mmap_file(struct file *file, unsigned long prot,
 	return 0;
 }
 
+static inline int security_mmap_backing_file(struct vm_area_struct *vma,
+					     struct file *backing_file,
+					     struct file *user_file)
+{
+	return 0;
+}
+
 static inline int security_mmap_addr(unsigned long addr)
 {
 	return cap_mmap_addr(addr);
diff --git a/security/security.c b/security/security.c
index 1794860fd614..4b61766c3d27 100644
--- a/security/security.c
+++ b/security/security.c
@@ -78,6 +78,7 @@ struct security_hook_heads security_hook_heads __ro_after_init;
 static BLOCKING_NOTIFIER_HEAD(blocking_lsm_notifier_chain);
 
 static struct kmem_cache *lsm_file_cache;
+static struct kmem_cache *lsm_backing_file_cache;
 static struct kmem_cache *lsm_inode_cache;
 
 char *lsm_names;
@@ -200,6 +201,8 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)
 
 	lsm_set_blob_size(&needed->lbs_cred, &blob_sizes.lbs_cred);
 	lsm_set_blob_size(&needed->lbs_file, &blob_sizes.lbs_file);
+	lsm_set_blob_size(&needed->lbs_backing_file,
+			     &blob_sizes.lbs_backing_file);
 	/*
 	 * The inode blob gets an rcu_head in addition to
 	 * what the modules might need.
@@ -374,6 +377,7 @@ static void __init ordered_lsm_init(void)
 
 	init_debug("cred blob size       = %d\n", blob_sizes.lbs_cred);
 	init_debug("file blob size       = %d\n", blob_sizes.lbs_file);
+	init_debug("backing_file blob size  = %d\n", blob_sizes.lbs_backing_file);
 	init_debug("inode blob size      = %d\n", blob_sizes.lbs_inode);
 	init_debug("ipc blob size        = %d\n", blob_sizes.lbs_ipc);
 	init_debug("msg_msg blob size    = %d\n", blob_sizes.lbs_msg_msg);
@@ -388,6 +392,11 @@ static void __init ordered_lsm_init(void)
 		lsm_file_cache = kmem_cache_create("lsm_file_cache",
 						   blob_sizes.lbs_file, 0,
 						   SLAB_PANIC, NULL);
+	if (blob_sizes.lbs_backing_file)
+		lsm_backing_file_cache = kmem_cache_create(
+						   "lsm_backing_file_cache",
+						   blob_sizes.lbs_backing_file,
+						   0, SLAB_PANIC, NULL);
 	if (blob_sizes.lbs_inode)
 		lsm_inode_cache = kmem_cache_create("lsm_inode_cache",
 						    blob_sizes.lbs_inode, 0,
@@ -616,6 +625,30 @@ static int lsm_file_alloc(struct file *file)
 	return 0;
 }
 
+/**
+ * lsm_backing_file_alloc - allocate a composite backing file blob
+ * @backing_file: the backing file
+ *
+ * Allocate the backing file blob for all the modules.
+ *
+ * Returns 0, or -ENOMEM if memory can't be allocated.
+ */
+static int lsm_backing_file_alloc(struct file *backing_file)
+{
+	void *blob;
+
+	if (!lsm_backing_file_cache) {
+		backing_file_set_security(backing_file, NULL);
+		return 0;
+	}
+
+	blob = kmem_cache_zalloc(lsm_backing_file_cache, GFP_KERNEL);
+	backing_file_set_security(backing_file, blob);
+	if (!blob)
+		return -ENOMEM;
+	return 0;
+}
+
 /**
  * lsm_inode_alloc - allocate a composite inode blob
  * @inode: the inode that needs a blob
@@ -2630,6 +2663,57 @@ void security_file_free(struct file *file)
 	}
 }
 
+/**
+ * security_backing_file_alloc() - Allocate and setup a backing file blob
+ * @backing_file: the backing file
+ * @user_file: the associated user visible file
+ *
+ * Allocate a backing file LSM blob and perform any necessary initialization of
+ * the LSM blob.  There will be some operations where the LSM will not have
+ * access to @user_file after this point, so any important state associated
+ * with @user_file that is important to the LSM should be captured in the
+ * backing file's LSM blob.
+ *
+ * LSM's should avoid taking a reference to @user_file in this hook as it will
+ * result in problems later when the system attempts to drop/put the file
+ * references due to a circular dependency.
+ *
+ * Return: Return 0 if the hook is successful, negative values otherwise.
+ */
+int security_backing_file_alloc(struct file *backing_file,
+				const struct file *user_file)
+{
+	int rc;
+
+	rc = lsm_backing_file_alloc(backing_file);
+	if (rc)
+		return rc;
+	rc = call_int_hook(backing_file_alloc, 0, backing_file, user_file);
+	if (unlikely(rc))
+		security_backing_file_free(backing_file);
+
+	return rc;
+}
+
+/**
+ * security_backing_file_free() - Free a backing file blob
+ * @backing_file: the backing file
+ *
+ * Free any LSM state associate with a backing file's LSM blob, including the
+ * blob itself.
+ */
+void security_backing_file_free(struct file *backing_file)
+{
+	void *blob = backing_file_security(backing_file);
+
+	call_void_hook(backing_file_free, backing_file);
+
+	if (blob) {
+		backing_file_set_security(backing_file, NULL);
+		kmem_cache_free(lsm_backing_file_cache, blob);
+	}
+}
+
 /**
  * security_file_ioctl() - Check if an ioctl is allowed
  * @file: associated file
@@ -2723,6 +2807,32 @@ int security_mmap_file(struct file *file, unsigned long prot,
 	return ima_file_mmap(file, prot, prot_adj, flags);
 }
 
+/**
+ * security_mmap_backing_file - Check if mmap'ing a backing file is allowed
+ * @vma: the vm_area_struct for the mmap'd region
+ * @backing_file: the backing file being mmap'd
+ * @user_file: the user file being mmap'd
+ *
+ * Check permissions for a mmap operation on a stacked filesystem.  This hook
+ * is called after the security_mmap_file() and is responsible for authorizing
+ * the mmap on @backing_file.  It is important to note that the mmap operation
+ * on @user_file has already been authorized and the @vma->vm_file has been
+ * set to @backing_file.
+ *
+ * Return: Returns 0 if permission is granted.
+ */
+int security_mmap_backing_file(struct vm_area_struct *vma,
+			       struct file *backing_file,
+			       struct file *user_file)
+{
+	/* recommended by the stackable filesystem devs */
+	if (WARN_ON_ONCE(!(backing_file->f_mode & FMODE_BACKING)))
+		return -EIO;
+
+	return call_int_hook(mmap_backing_file, 0, vma, backing_file, user_file);
+}
+EXPORT_SYMBOL_GPL(security_mmap_backing_file);
+
 /**
  * security_mmap_addr() - Check if mmap'ing an address is allowed
  * @addr: address
-- 
2.18.0.huawei.25

Re: [PATCH v2 stable/linux-6.6.y 2/3] lsm: add backing_file LSM hooks

[sashiko-bot]

> From: Paul Moore <paul@paul-moore.com>
> 
> [ Upstream commit 6af36aeb147a06dea47c49859cd6ca5659aeb987 ]
> 
> Stacked filesystems such as overlayfs do not currently provide the
> necessary mechanisms for LSMs to properly enforce access controls on the
> mmap() and mprotect() operations.  In order to resolve this gap, a LSM
> security blob is being added to the backing_file struct and the following
> new LSM hooks are being created:
> 
>  security_backing_file_alloc()
>  security_backing_file_free()
>  security_mmap_backing_file()
> 
> The first two hooks are to manage the lifecycle of the LSM security blob
> [ ... ]
> are dropped in the 6.6 LTS backport.
> 
> 4. Use macro backing_file to replace inline function to eliminate the
> const warning.]
> Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260627065720.1945589-1-caixinchen1@huawei.com?part=2

[PATCH v2 stable/linux-6.6.y 3/3] selinux: fix overlayfs mmap() and mprotect() access checks

[Cai Xinchen]

From: Paul Moore <paul@paul-moore.com>

[ Upstream commit 82544d36b1729153c8aeb179e84750f0c085d3b1 ]

The existing SELinux security model for overlayfs is to allow access if
the current task is able to access the top level file (the "user" file)
and the mounter's credentials are sufficient to access the lower
level file (the "backing" file).  Unfortunately, the current code does
not properly enforce these access controls for both mmap() and mprotect()
operations on overlayfs filesystems.

This patch makes use of the newly created security_mmap_backing_file()
LSM hook to provide the missing backing file enforcement for mmap()
operations, and leverages the backing file API and new LSM blob to
provide the necessary information to properly enforce the mprotect()
access controls.

Cc: stable@vger.kernel.org
Acked-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
[backing_file_user_path() not available
Mainline uses backing_file_user_path(file) to obtain the user-visible path
from a backing file. The 6.6.y version uses &file->f_path directly]
Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>
---
 security/selinux/hooks.c          | 242 ++++++++++++++++++++++--------
 security/selinux/include/objsec.h |  11 ++
 2 files changed, 189 insertions(+), 64 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 60092d0b013c..3f11c5ae8fbf 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1717,49 +1717,72 @@ static inline int file_path_has_perm(const struct cred *cred,
 static int bpf_fd_pass(const struct file *file, u32 sid);
 #endif
 
-/* Check whether a task can use an open file descriptor to
-   access an inode in a given way.  Check access to the
-   descriptor itself, and then use dentry_has_perm to
-   check a particular permission to the file.
-   Access to the descriptor is implicitly granted if it
-   has the same SID as the process.  If av is zero, then
-   access to the file is not checked, e.g. for cases
-   where only the descriptor is affected like seek. */
-static int file_has_perm(const struct cred *cred,
-			 struct file *file,
-			 u32 av)
+static int __file_has_perm(const struct cred *cred, const struct file *file,
+			   u32 av, bool bf_user_file)
+
 {
-	struct file_security_struct *fsec = selinux_file(file);
-	struct inode *inode = file_inode(file);
 	struct common_audit_data ad;
-	u32 sid = cred_sid(cred);
+	struct inode *inode;
+	u32 ssid = cred_sid(cred);
+	u32 tsid_fd;
 	int rc;
 
-	ad.type = LSM_AUDIT_DATA_FILE;
-	ad.u.file = file;
+	if (bf_user_file) {
+		struct backing_file_security_struct *bfsec;
+		const struct path *path;
 
-	if (sid != fsec->sid) {
-		rc = avc_has_perm(sid, fsec->sid,
-				  SECCLASS_FD,
-				  FD__USE,
-				  &ad);
+		if (WARN_ON(!(file->f_mode & FMODE_BACKING)))
+			return -EIO;
+
+		bfsec = selinux_backing_file(file);
+		path = &file->f_path;
+		tsid_fd = bfsec->uf_sid;
+		inode = d_inode(path->dentry);
+
+		ad.type = LSM_AUDIT_DATA_PATH;
+		ad.u.path = *path;
+	} else {
+		struct file_security_struct *fsec = selinux_file(file);
+
+		tsid_fd = fsec->sid;
+		inode = file_inode(file);
+
+		ad.type = LSM_AUDIT_DATA_FILE;
+		ad.u.file = file;
+	}
+
+	if (ssid != tsid_fd) {
+		rc = avc_has_perm(ssid, tsid_fd, SECCLASS_FD, FD__USE, &ad);
 		if (rc)
-			goto out;
+			return rc;
 	}
 
 #ifdef CONFIG_BPF_SYSCALL
-	rc = bpf_fd_pass(file, cred_sid(cred));
+	/* regardless of backing vs user file, use the underlying file here */
+	rc = bpf_fd_pass(file, ssid);
 	if (rc)
 		return rc;
 #endif
 
 	/* av is zero if only checking access to the descriptor. */
-	rc = 0;
 	if (av)
-		rc = inode_has_perm(cred, inode, av, &ad);
+		return inode_has_perm(cred, inode, av, &ad);
 
-out:
-	return rc;
+	return 0;
+}
+
+/* Check whether a task can use an open file descriptor to
+   access an inode in a given way.  Check access to the
+   descriptor itself, and then use dentry_has_perm to
+   check a particular permission to the file.
+   Access to the descriptor is implicitly granted if it
+   has the same SID as the process.  If av is zero, then
+   access to the file is not checked, e.g. for cases
+   where only the descriptor is affected like seek. */
+static inline int file_has_perm(const struct cred *cred,
+				const struct file *file, u32 av)
+{
+	return __file_has_perm(cred, file, av, false);
 }
 
 /*
@@ -3638,6 +3661,17 @@ static int selinux_file_alloc_security(struct file *file)
 	return 0;
 }
 
+static int selinux_backing_file_alloc(struct file *backing_file,
+				      const struct file *user_file)
+{
+	struct backing_file_security_struct *bfsec;
+
+	bfsec = selinux_backing_file(backing_file);
+	bfsec->uf_sid = selinux_file(user_file)->sid;
+
+	return 0;
+}
+
 /*
  * Check whether a task has the ioctl permission and cmd
  * operation to an inode.
@@ -3755,42 +3789,55 @@ static int selinux_file_ioctl_compat(struct file *file, unsigned int cmd,
 
 static int default_noexec __ro_after_init;
 
-static int file_map_prot_check(struct file *file, unsigned long prot, int shared)
+static int __file_map_prot_check(const struct cred *cred,
+				 const struct file *file, unsigned long prot,
+				 bool shared, bool bf_user_file)
 {
-	const struct cred *cred = current_cred();
-	u32 sid = cred_sid(cred);
-	int rc = 0;
+	struct inode *inode = NULL;
+	bool prot_exec = prot & PROT_EXEC;
+	bool prot_write = prot & PROT_WRITE;
+
+	if (file) {
+		if (bf_user_file)
+			inode = d_inode(file->f_path.dentry);
+		else
+			inode = file_inode(file);
+	}
+
+	if (default_noexec && prot_exec &&
+	    (!file || IS_PRIVATE(inode) || (!shared && prot_write))) {
+		int rc;
+		u32 sid = cred_sid(cred);
 
-	if (default_noexec &&
-	    (prot & PROT_EXEC) && (!file || IS_PRIVATE(file_inode(file)) ||
-				   (!shared && (prot & PROT_WRITE)))) {
 		/*
-		 * We are making executable an anonymous mapping or a
-		 * private file mapping that will also be writable.
-		 * This has an additional check.
+		 * We are making executable an anonymous mapping or a private
+		 * file mapping that will also be writable.
 		 */
-		rc = avc_has_perm(sid, sid, SECCLASS_PROCESS,
-				  PROCESS__EXECMEM, NULL);
+		rc = avc_has_perm(sid, sid, SECCLASS_PROCESS, PROCESS__EXECMEM,
+				  NULL);
 		if (rc)
-			goto error;
+			return rc;
 	}
 
 	if (file) {
-		/* read access is always possible with a mapping */
+		/* "read" always possible, "write" only if shared */
 		u32 av = FILE__READ;
-
-		/* write access only matters if the mapping is shared */
-		if (shared && (prot & PROT_WRITE))
+		if (shared && prot_write)
 			av |= FILE__WRITE;
-
-		if (prot & PROT_EXEC)
+		if (prot_exec)
 			av |= FILE__EXECUTE;
 
-		return file_has_perm(cred, file, av);
+		return __file_has_perm(cred, file, av, bf_user_file);
 	}
 
-error:
-	return rc;
+	return 0;
+}
+
+static inline int file_map_prot_check(const struct cred *cred,
+				      const struct file *file,
+				      unsigned long prot, bool shared)
+{
+	return __file_map_prot_check(cred, file, prot, shared, false);
 }
 
 static int selinux_mmap_addr(unsigned long addr)
@@ -3806,36 +3853,80 @@ static int selinux_mmap_addr(unsigned long addr)
 	return rc;
 }
 
-static int selinux_mmap_file(struct file *file,
-			     unsigned long reqprot __always_unused,
-			     unsigned long prot, unsigned long flags)
+static int selinux_mmap_file_common(const struct cred *cred, struct file *file,
+				    unsigned long prot, bool shared)
 {
-	struct common_audit_data ad;
-	int rc;
-
 	if (file) {
+		int rc;
+		struct common_audit_data ad;
+
 		ad.type = LSM_AUDIT_DATA_FILE;
 		ad.u.file = file;
-		rc = inode_has_perm(current_cred(), file_inode(file),
-				    FILE__MAP, &ad);
+		rc = inode_has_perm(cred, file_inode(file), FILE__MAP, &ad);
 		if (rc)
 			return rc;
 	}
 
-	return file_map_prot_check(file, prot,
-				   (flags & MAP_TYPE) == MAP_SHARED);
+	return file_map_prot_check(cred, file, prot, shared);
+}
+
+static int selinux_mmap_file(struct file *file,
+			     unsigned long reqprot __always_unused,
+			     unsigned long prot, unsigned long flags)
+{
+	return selinux_mmap_file_common(current_cred(), file, prot,
+					(flags & MAP_TYPE) == MAP_SHARED);
+}
+
+/**
+ * selinux_mmap_backing_file - Check mmap permissions on a backing file
+ * @vma: memory region
+ * @backing_file: stacked filesystem backing file
+ * @user_file: user visible file
+ *
+ * This is called after selinux_mmap_file() on stacked filesystems, and it
+ * is this function's responsibility to verify access to @backing_file and
+ * setup the SELinux state for possible later use in the mprotect() code path.
+ *
+ * By the time this function is called, mmap() access to @user_file has already
+ * been authorized and @vma->vm_file has been set to point to @backing_file.
+ *
+ * Return zero on success, negative values otherwise.
+ */
+static int selinux_mmap_backing_file(struct vm_area_struct *vma,
+				     struct file *backing_file,
+				     struct file *user_file __always_unused)
+{
+	unsigned long prot = 0;
+
+	/* translate vma->vm_flags perms into PROT perms */
+	if (vma->vm_flags & VM_READ)
+		prot |= PROT_READ;
+	if (vma->vm_flags & VM_WRITE)
+		prot |= PROT_WRITE;
+	if (vma->vm_flags & VM_EXEC)
+		prot |= PROT_EXEC;
+
+	return selinux_mmap_file_common(backing_file->f_cred, backing_file,
+					prot, vma->vm_flags & VM_SHARED);
 }
 
 static int selinux_file_mprotect(struct vm_area_struct *vma,
 				 unsigned long reqprot __always_unused,
 				 unsigned long prot)
 {
+	int rc;
 	const struct cred *cred = current_cred();
 	u32 sid = cred_sid(cred);
+	const struct file *file = vma->vm_file;
+	bool backing_file;
+	bool shared = vma->vm_flags & VM_SHARED;
+
+	/* check if we need to trigger the "backing files are awful" mode */
+	backing_file = file && (file->f_mode & FMODE_BACKING);
 
 	if (default_noexec &&
 	    (prot & PROT_EXEC) && !(vma->vm_flags & VM_EXEC)) {
-		int rc = 0;
 		/*
 		 * We don't use the vma_is_initial_heap() helper as it has
 		 * a history of problems and is currently broken on systems
@@ -3849,11 +3940,15 @@ static int selinux_file_mprotect(struct vm_area_struct *vma,
 		    vma->vm_end <= vma->vm_mm->brk) {
 			rc = avc_has_perm(sid, sid, SECCLASS_PROCESS,
 					  PROCESS__EXECHEAP, NULL);
-		} else if (!vma->vm_file && (vma_is_initial_stack(vma) ||
+			if (rc)
+				return rc;
+		} else if (!file && (vma_is_initial_stack(vma) ||
 			    vma_is_stack_for_current(vma))) {
 			rc = avc_has_perm(sid, sid, SECCLASS_PROCESS,
 					  PROCESS__EXECSTACK, NULL);
-		} else if (vma->vm_file && vma->anon_vma) {
+			if (rc)
+				return rc;
+		} else if (file && vma->anon_vma) {
 			/*
 			 * We are making executable a file mapping that has
 			 * had some COW done. Since pages might have been
@@ -3861,13 +3956,29 @@ static int selinux_file_mprotect(struct vm_area_struct *vma,
 			 * modified content.  This typically should only
 			 * occur for text relocations.
 			 */
-			rc = file_has_perm(cred, vma->vm_file, FILE__EXECMOD);
+			rc = __file_has_perm(cred, file, FILE__EXECMOD,
+					     backing_file);
+			if (rc)
+				return rc;
+			if (backing_file) {
+				rc = file_has_perm(file->f_cred, file,
+						   FILE__EXECMOD);
+				if (rc)
+					return rc;
+			}
 		}
+	}
+
+	rc = __file_map_prot_check(cred, file, prot, shared, backing_file);
+	if (rc)
+		return rc;
+	if (backing_file) {
+		rc = file_map_prot_check(file->f_cred, file, prot, shared);
 		if (rc)
 			return rc;
 	}
 
-	return file_map_prot_check(vma->vm_file, prot, vma->vm_flags&VM_SHARED);
+	return 0;
 }
 
 static int selinux_file_lock(struct file *file, unsigned int cmd)
@@ -6870,6 +6981,7 @@ static void selinux_bpf_prog_free(struct bpf_prog_aux *aux)
 struct lsm_blob_sizes selinux_blob_sizes __ro_after_init = {
 	.lbs_cred = sizeof(struct task_security_struct),
 	.lbs_file = sizeof(struct file_security_struct),
+	.lbs_backing_file = sizeof(struct backing_file_security_struct),
 	.lbs_inode = sizeof(struct inode_security_struct),
 	.lbs_ipc = sizeof(struct ipc_security_struct),
 	.lbs_msg_msg = sizeof(struct msg_security_struct),
@@ -7074,9 +7186,11 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
 
 	LSM_HOOK_INIT(file_permission, selinux_file_permission),
 	LSM_HOOK_INIT(file_alloc_security, selinux_file_alloc_security),
+	LSM_HOOK_INIT(backing_file_alloc, selinux_backing_file_alloc),
 	LSM_HOOK_INIT(file_ioctl, selinux_file_ioctl),
 	LSM_HOOK_INIT(file_ioctl_compat, selinux_file_ioctl_compat),
 	LSM_HOOK_INIT(mmap_file, selinux_mmap_file),
+	LSM_HOOK_INIT(mmap_backing_file, selinux_mmap_backing_file),
 	LSM_HOOK_INIT(mmap_addr, selinux_mmap_addr),
 	LSM_HOOK_INIT(file_mprotect, selinux_file_mprotect),
 	LSM_HOOK_INIT(file_lock, selinux_file_lock),
diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
index 8159fd53c3de..541933dd295c 100644
--- a/security/selinux/include/objsec.h
+++ b/security/selinux/include/objsec.h
@@ -60,6 +60,10 @@ struct file_security_struct {
 	u32 pseqno;		/* Policy seqno at the time of file open */
 };
 
+struct backing_file_security_struct {
+	u32 uf_sid; /* associated user file fsec->sid */
+};
+
 struct superblock_security_struct {
 	u32 sid;			/* SID of file system superblock */
 	u32 def_sid;			/* default SID for labeling */
@@ -158,6 +162,13 @@ static inline struct file_security_struct *selinux_file(const struct file *file)
 	return file->f_security + selinux_blob_sizes.lbs_file;
 }
 
+static inline struct backing_file_security_struct *
+selinux_backing_file(const struct file *backing_file)
+{
+	void *blob = backing_file_security(backing_file);
+	return blob + selinux_blob_sizes.lbs_backing_file;
+}
+
 static inline struct inode_security_struct *selinux_inode(
 						const struct inode *inode)
 {
-- 
2.18.0.huawei.25

Re: [PATCH v2 stable/linux-6.6.y 3/3] selinux: fix overlayfs mmap() and mprotect() access checks

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Spurious SELinux denial due to checking PROCESS__EXECMEM against mounter's credentials
--

commit 8203c8d28a621e846a03edb5074214a597c8b58e
Author: Paul Moore <paul@paul-moore.com>

selinux: fix overlayfs mmap() and mprotect() access checks

This commit introduces SELinux backing file enforcement for mmap() and
mprotect() on overlayfs filesystems. It uses the new backing file API and
LSM blobs to enforce access controls against both the user file and the
backing file.

> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 60092d0b013ce..3f11c5ae8fbf0 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
[ ... ]
> @@ -3789,17 +3789,28 @@ static int default_noexec __ro_after_init;
>  
> -static int file_map_prot_check(struct file *file, unsigned long prot, int shared)
> +static int __file_map_prot_check(const struct cred *cred,
> +				 const struct file *file, unsigned long prot,
> +				 bool shared, bool bf_user_file)
>  {
[ ... ]
> +	if (default_noexec && prot_exec &&
> +	    (!file || IS_PRIVATE(inode) || (!shared && prot_write))) {
> +		int rc;
> +		u32 sid = cred_sid(cred);
>  
> -		rc = avc_has_perm(sid, sid, SECCLASS_PROCESS,
> -				  PROCESS__EXECMEM, NULL);
> +		/*
> +		 * We are making executable an anonymous mapping or a private
> +		 * file mapping that will also be writable.
> +		 */
> +		rc = avc_has_perm(sid, sid, SECCLASS_PROCESS, PROCESS__EXECMEM,
> +				  NULL);
> +		if (rc)
> +			return rc;

[Severity: High]
When checking PROCESS__EXECMEM, does this inadvertently use the mounter's
credential instead of the current task's credential when called for a
backing file?

Since cred_sid(cred) relies on the passed-in cred argument, if the caller
passes the backing file's credentials, we will check if the mounter has
PROCESS__EXECMEM. Could this lead to spurious SELinux denials for a user
process trying to create a private writable executable mapping (W^X) on
overlayfs, simply because the mounter lacks the execmem permission?

[ ... ]
> @@ -3806,36 +3853,80 @@ static int selinux_mmap_addr(unsigned long addr)
[ ... ]
> +static int selinux_mmap_backing_file(struct vm_area_struct *vma,
> +				     struct file *backing_file,
> +				     struct file *user_file __always_unused)
> +{
> +	unsigned long prot = 0;
> +
> +	/* translate vma->vm_flags perms into PROT perms */
> +	if (vma->vm_flags & VM_READ)
> +		prot |= PROT_READ;
> +	if (vma->vm_flags & VM_WRITE)
> +		prot |= PROT_WRITE;
> +	if (vma->vm_flags & VM_EXEC)
> +		prot |= PROT_EXEC;
> +
> +	return selinux_mmap_file_common(backing_file->f_cred, backing_file,
> +					prot, vma->vm_flags & VM_SHARED);
>  }

[Severity: High]
Does passing backing_file->f_cred here trigger the PROCESS__EXECMEM check
against the mounter rather than the current process during an mmap() system
call?

[ ... ]
> @@ -3849,11 +3940,15 @@ static int selinux_file_mprotect(struct vm_area_struct *vma,
[ ... ]
> +	rc = __file_map_prot_check(cred, file, prot, shared, backing_file);
> +	if (rc)
> +		return rc;
> +	if (backing_file) {
> +		rc = file_map_prot_check(file->f_cred, file, prot, shared);
>  		if (rc)
>  			return rc;
>  	}
>  
> -	return file_map_prot_check(vma->vm_file, prot, vma->vm_flags&VM_SHARED);
> +	return 0;
>  }

[Severity: High]
Similarly, does passing file->f_cred to file_map_prot_check() cause the
same issue for mprotect(), checking PROCESS__EXECMEM against the mounter's
credentials?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260627065720.1945589-1-caixinchen1@huawei.com?part=3

Re: [PATCH v2 stable/linux-6.6.y 0/3] Backport Fix incorrect overlayfs mmap() and mprotect() LSM access controls

[Sasha Levin]

On Sat, Jun 27, 2026 at 02:57:17PM +0800, Cai Xinchen wrote:
> [PATCH v2 stable/linux-6.6.y 0/3] Backport Fix incorrect overlayfs
> mmap() and mprotect() LSM access controls

All three patches are queued for 6.6, thanks.

--
Thanks,
Sasha