* [PATCH v3 0/2] Fix incorrect overlayfs mmap() and mprotect() LSM access controls
@ 2026-03-27 22:04 Paul Moore
2026-03-27 22:04 ` [PATCH v3 1/2] lsm: add backing_file LSM hooks Paul Moore
2026-03-27 22:04 ` [PATCH v3 2/2] selinux: fix overlayfs mmap() and mprotect() access checks Paul Moore
0 siblings, 2 replies; 7+ messages in thread
From: Paul Moore @ 2026-03-27 22:04 UTC (permalink / raw)
To: linux-security-module, selinux, linux-fsdevel, linux-unionfs,
linux-erofs
Cc: Amir Goldstein, Gao Xiang, Christian Brauner
A very minor update to the v2 patchset[2] posted earlier this week. The
changelog is below. The primary reason for posting such a lightly revised
patchset is to drop the "RFC" qualifier as I've had the opportunity to do
additional testing and I'm reasonably happy with the results. As always,
anyone reading this is welcome, and encouraged, to do any additional
testing they believe might be helpful.
I plan to merge this into lsm/stable-7.0 either later tonight, or sometime
over the weekend, so the patchset has some time in linux-next. As we're
fairly close to the v7.1 merge window, I may decide to hold this for Linus
until then; let's see how things turn out with linux-next as well as any
additional review comments.
[2] https://lore.kernel.org/linux-security-module/20260323042510.3331778-4-paul@paul-moore.com/
--
CHANGELOG:
v3:
- fix the LSM hook stubs (kernel robot, Ryan Lee)
- fix the lsm_backing_file_cache allocation size (Ryan Lee)
- minor style, simplicity tweaks to the SELinux patch
v2:
- remove the user O_PATH file patch from Amir
- add the backing_file LSM blob and lifecycle hooks
- update the SELinux code to reflect the other changes
v1:
- initial version
--
Paul Moore (2):
lsm: add backing_file LSM hooks
selinux: fix overlayfs mmap() and mprotect() access checks
fs/backing-file.c | 18 +-
fs/erofs/ishare.c | 10 +
fs/file_table.c | 21 ++
fs/fuse/passthrough.c | 2
fs/internal.h | 3
fs/overlayfs/dir.c | 2
fs/overlayfs/file.c | 2
include/linux/backing-file.h | 4
include/linux/fs.h | 1
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/lsm.h | 1
security/lsm_init.c | 9 +
security/security.c | 100 +++++++++++
security/selinux/hooks.c | 256 +++++++++++++++++++++---------
security/selinux/include/objsec.h | 17 +
18 files changed, 389 insertions(+), 87 deletions(-)
^ permalink raw reply [flat|nested] 7+ messages in thread* [PATCH v3 1/2] lsm: add backing_file LSM hooks 2026-03-27 22:04 [PATCH v3 0/2] Fix incorrect overlayfs mmap() and mprotect() LSM access controls Paul Moore @ 2026-03-27 22:04 ` Paul Moore 2026-03-28 8:29 ` Amir Goldstein 2026-03-30 8:35 ` Amir Goldstein 2026-03-27 22:04 ` [PATCH v3 2/2] selinux: fix overlayfs mmap() and mprotect() access checks Paul Moore 1 sibling, 2 replies; 7+ messages in thread From: Paul Moore @ 2026-03-27 22:04 UTC (permalink / raw) To: linux-security-module, selinux, linux-fsdevel, linux-unionfs, linux-erofs Cc: Amir Goldstein, Gao Xiang, Christian Brauner 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 two other small changes to support these new LSM hooks. We 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, and we 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 Acked-by: Christian Brauner <brauner@kernel.org> Signed-off-by: Paul Moore <paul@paul-moore.com> --- fs/backing-file.c | 18 ++++-- fs/erofs/ishare.c | 10 +++- fs/file_table.c | 21 ++++++- fs/fuse/passthrough.c | 2 +- fs/internal.h | 3 +- fs/overlayfs/dir.c | 2 +- fs/overlayfs/file.c | 2 +- include/linux/backing-file.h | 4 +- include/linux/fs.h | 1 + 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/lsm.h | 1 + security/lsm_init.c | 9 +++ security/security.c | 100 ++++++++++++++++++++++++++++++++++ 16 files changed, 187 insertions(+), 16 deletions(-) diff --git a/fs/backing-file.c b/fs/backing-file.c index 45da8600d564..1f3bbfc75882 100644 --- a/fs/backing-file.c +++ b/fs/backing-file.c @@ -12,6 +12,7 @@ #include <linux/backing-file.h> #include <linux/splice.h> #include <linux/mm.h> +#include <linux/security.h> #include "internal.h" @@ -29,14 +30,15 @@ * returned file into a container structure that also stores the stacked * file's path, which can be retrieved using backing_file_user_path(). */ -struct file *backing_file_open(const struct path *user_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; @@ -52,15 +54,16 @@ struct file *backing_file_open(const struct path *user_path, int flags, } EXPORT_SYMBOL_GPL(backing_file_open); -struct file *backing_tmpfile_open(const struct path *user_path, int flags, +struct file *backing_tmpfile_open(const struct file *user_file, int flags, const struct path *real_parentpath, umode_t mode, const struct cred *cred) { struct mnt_idmap *real_idmap = mnt_idmap(real_parentpath->mnt); + 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; @@ -336,8 +339,13 @@ int backing_file_mmap(struct file *file, struct vm_area_struct *vma, vma_set_file(vma, file); - scoped_with_creds(ctx->cred) + scoped_with_creds(ctx->cred) { + ret = security_mmap_backing_file(vma, file, user_file); + if (ret) + return ret; + ret = vfs_mmap(vma->vm_file, vma); + } if (ctx->accessed) ctx->accessed(user_file); diff --git a/fs/erofs/ishare.c b/fs/erofs/ishare.c index 829d50d5c717..ec3fc5ac1a55 100644 --- a/fs/erofs/ishare.c +++ b/fs/erofs/ishare.c @@ -4,6 +4,7 @@ */ #include <linux/xxhash.h> #include <linux/mount.h> +#include <linux/security.h> #include "internal.h" #include "xattr.h" @@ -106,7 +107,8 @@ static int erofs_ishare_file_open(struct inode *inode, struct file *file) if (file->f_flags & O_DIRECT) return -EINVAL; - realfile = alloc_empty_backing_file(O_RDONLY|O_NOATIME, current_cred()); + realfile = alloc_empty_backing_file(O_RDONLY|O_NOATIME, current_cred(), + file); if (IS_ERR(realfile)) return PTR_ERR(realfile); ihold(sharedinode); @@ -150,8 +152,14 @@ static ssize_t erofs_ishare_file_read_iter(struct kiocb *iocb, static int erofs_ishare_mmap(struct file *file, struct vm_area_struct *vma) { struct file *realfile = file->private_data; + int err; vma_set_file(vma, realfile); + + err = security_mmap_backing_file(vma, realfile, file); + if (err) + return err; + return generic_file_readonly_mmap(file, vma); } diff --git a/fs/file_table.c b/fs/file_table.c index aaa5faaace1e..0bdc26cae138 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -50,6 +50,7 @@ struct backing_file { struct path user_path; freeptr_t bf_freeptr; }; + void *security; }; #define backing_file(f) container_of(f, struct backing_file, file) @@ -66,6 +67,11 @@ void backing_file_set_user_path(struct file *f, const struct path *path) } EXPORT_SYMBOL_GPL(backing_file_set_user_path); +void *backing_file_security(const struct file *f) +{ + return backing_file(f)->security; +} + static inline void file_free(struct file *f) { security_file_free(f); @@ -73,8 +79,11 @@ static inline void file_free(struct file *f) percpu_counter_dec(&nr_files); put_cred(f->f_cred); if (unlikely(f->f_mode & FMODE_BACKING)) { - path_put(backing_file_user_path(f)); - kmem_cache_free(bfilp_cachep, backing_file(f)); + struct backing_file *ff = backing_file(f); + + security_backing_file_free(&ff->security); + path_put(&ff->user_path); + kmem_cache_free(bfilp_cachep, ff); } else { kmem_cache_free(filp_cachep, f); } @@ -290,7 +299,8 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred) * 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; @@ -306,6 +316,11 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred) } ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT; + error = security_backing_file_alloc(&ff->security, user_file); + if (unlikely(error)) { + fput(&ff->file); + return ERR_PTR(error); + } return &ff->file; } EXPORT_SYMBOL_GPL(alloc_empty_backing_file); diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c index 72de97c03d0e..f2d08ac2459b 100644 --- a/fs/fuse/passthrough.c +++ b/fs/fuse/passthrough.c @@ -167,7 +167,7 @@ struct fuse_backing *fuse_passthrough_open(struct file *file, int backing_id) goto out; /* Allocate backing file per fuse file to store fuse path */ - backing_file = backing_file_open(&file->f_path, file->f_flags, + backing_file = backing_file_open(file, file->f_flags, &fb->file->f_path, fb->cred); err = PTR_ERR(backing_file); if (IS_ERR(backing_file)) { diff --git a/fs/internal.h b/fs/internal.h index cbc384a1aa09..77e90e4124e0 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -106,7 +106,8 @@ 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); void backing_file_set_user_path(struct file *f, const struct path *path); static inline void file_put_write_access(struct file *file) diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index ff3dbd1ca61f..f2f20a611af3 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -1374,7 +1374,7 @@ static int ovl_create_tmpfile(struct file *file, struct dentry *dentry, return PTR_ERR(cred); ovl_path_upper(dentry->d_parent, &realparentpath); - realfile = backing_tmpfile_open(&file->f_path, flags, &realparentpath, + realfile = backing_tmpfile_open(file, flags, &realparentpath, mode, current_cred()); err = PTR_ERR_OR_ZERO(realfile); pr_debug("tmpfile/open(%pd2, 0%o) = %i\n", realparentpath.dentry, mode, err); diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index 97bed2286030..27cc07738f33 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -48,7 +48,7 @@ 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_user_path(file), + realfile = backing_file_open(file, flags, realpath, current_cred()); } } diff --git a/include/linux/backing-file.h b/include/linux/backing-file.h index 1476a6ed1bfd..c939cd222730 100644 --- a/include/linux/backing-file.h +++ b/include/linux/backing-file.h @@ -18,10 +18,10 @@ struct backing_file_ctx { void (*end_write)(struct kiocb *iocb, ssize_t); }; -struct file *backing_file_open(const struct path *user_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 file *backing_tmpfile_open(const struct path *user_path, int flags, +struct file *backing_tmpfile_open(const struct file *user_file, int flags, const struct path *real_parentpath, umode_t mode, const struct cred *cred); ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter, diff --git a/include/linux/fs.h b/include/linux/fs.h index 8b3dd145b25e..8f5702cfb5e0 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2474,6 +2474,7 @@ struct file *dentry_open_nonotify(const struct path *path, int flags, struct file *dentry_create(struct path *path, int flags, umode_t mode, const struct cred *cred); const struct path *backing_file_user_path(const struct file *f); +void *backing_file_security(const struct file *f); /* * When mmapping a file on a stackable filesystem (e.g., overlayfs), the file diff --git a/include/linux/lsm_audit.h b/include/linux/lsm_audit.h index 382c56a97bba..584db296e43b 100644 --- a/include/linux/lsm_audit.h +++ b/include/linux/lsm_audit.h @@ -94,7 +94,7 @@ 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 8c42b4bde09c..2c4da40757ad 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -191,6 +191,9 @@ 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_release, struct file *file) LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file) +LSM_HOOK(int, 0, backing_file_alloc, void *backing_file_blobp, + const struct file *user_file) +LSM_HOOK(void, LSM_RET_VOID, backing_file_free, void *backing_file_blobp) 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, @@ -198,6 +201,8 @@ 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 d48bf0ad26f4..b4f8cad53ddb 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -104,6 +104,7 @@ struct security_hook_list { struct lsm_blob_sizes { unsigned int lbs_cred; unsigned int lbs_file; + unsigned int lbs_backing_file; unsigned int lbs_ib; unsigned int lbs_inode; unsigned int lbs_sock; diff --git a/include/linux/security.h b/include/linux/security.h index 83a646d72f6f..0a726bb70479 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -471,11 +471,17 @@ int security_file_permission(struct file *file, int mask); int security_file_alloc(struct file *file); void security_file_release(struct file *file); void security_file_free(struct file *file); +int security_backing_file_alloc(void **backing_file_blobp, + const struct file *user_file); +void security_backing_file_free(void **backing_file_blobp); 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); @@ -1140,6 +1146,15 @@ static inline void security_file_release(struct file *file) static inline void security_file_free(struct file *file) { } +static inline int security_backing_file_alloc(void **backing_file_blobp, + const struct file *user_file) +{ + return 0; +} + +static inline void security_backing_file_free(void **backing_file_blobp) +{ } + static inline int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { @@ -1159,6 +1174,13 @@ 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/lsm.h b/security/lsm.h index db77cc83e158..32f808ad4335 100644 --- a/security/lsm.h +++ b/security/lsm.h @@ -29,6 +29,7 @@ extern struct lsm_blob_sizes blob_sizes; /* LSM blob caches */ extern struct kmem_cache *lsm_file_cache; +extern struct kmem_cache *lsm_backing_file_cache; extern struct kmem_cache *lsm_inode_cache; /* LSM blob allocators */ diff --git a/security/lsm_init.c b/security/lsm_init.c index 573e2a7250c4..7c0fd17f1601 100644 --- a/security/lsm_init.c +++ b/security/lsm_init.c @@ -293,6 +293,8 @@ static void __init lsm_prepare(struct lsm_info *lsm) blobs = lsm->blobs; lsm_blob_size_update(&blobs->lbs_cred, &blob_sizes.lbs_cred); lsm_blob_size_update(&blobs->lbs_file, &blob_sizes.lbs_file); + lsm_blob_size_update(&blobs->lbs_backing_file, + &blob_sizes.lbs_backing_file); lsm_blob_size_update(&blobs->lbs_ib, &blob_sizes.lbs_ib); /* inode blob gets an rcu_head in addition to LSM blobs. */ if (blobs->lbs_inode && blob_sizes.lbs_inode == 0) @@ -441,6 +443,8 @@ int __init security_init(void) if (lsm_debug) { lsm_pr("blob(cred) size %d\n", blob_sizes.lbs_cred); lsm_pr("blob(file) size %d\n", blob_sizes.lbs_file); + lsm_pr("blob(backing_file) size %d\n", + blob_sizes.lbs_backing_file); lsm_pr("blob(ib) size %d\n", blob_sizes.lbs_ib); lsm_pr("blob(inode) size %d\n", blob_sizes.lbs_inode); lsm_pr("blob(ipc) size %d\n", blob_sizes.lbs_ipc); @@ -462,6 +466,11 @@ int __init security_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, diff --git a/security/security.c b/security/security.c index 67af9228c4e9..651a0d643c9f 100644 --- a/security/security.c +++ b/security/security.c @@ -81,6 +81,7 @@ const struct lsm_id *lsm_idlist[MAX_LSM_COUNT]; struct lsm_blob_sizes blob_sizes; struct kmem_cache *lsm_file_cache; +struct kmem_cache *lsm_backing_file_cache; struct kmem_cache *lsm_inode_cache; #define SECURITY_HOOK_ACTIVE_KEY(HOOK, IDX) security_hook_active_##HOOK##_##IDX @@ -172,6 +173,28 @@ static int lsm_file_alloc(struct file *file) return 0; } +/** + * lsm_backing_file_alloc - allocate a composite backing file blob + * @backing_file_blobp: pointer to the backing file LSM blob pointer + * + * 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(void **backing_file_blobp) +{ + if (!lsm_backing_file_cache) { + *backing_file_blobp = NULL; + return 0; + } + + *backing_file_blobp = kmem_cache_zalloc(lsm_backing_file_cache, + GFP_KERNEL); + if (*backing_file_blobp == NULL) + return -ENOMEM; + return 0; +} + /** * lsm_blob_alloc - allocate a composite blob * @dest: the destination for the blob @@ -2417,6 +2440,57 @@ void security_file_free(struct file *file) } } +/** + * security_backing_file_alloc() - Allocate and setup a backing file blob + * @backing_file_blobp: pointer to the backing file LSM blob pointer + * @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(void **backing_file_blobp, + const struct file *user_file) +{ + int rc; + + rc = lsm_backing_file_alloc(backing_file_blobp); + if (rc) + return rc; + rc = call_int_hook(backing_file_alloc, *backing_file_blobp, user_file); + if (unlikely(rc)) + security_backing_file_free(backing_file_blobp); + + return rc; +} + +/** + * security_backing_file_free() - Free a backing file blob + * @backing_file_blobp: pointer to the backing file LSM blob pointer + * + * Free any LSM state associate with a backing file's LSM blob, including the + * blob itself. + */ +void security_backing_file_free(void **backing_file_blobp) +{ + void *backing_file_blob = *backing_file_blobp; + + call_void_hook(backing_file_free, backing_file_blob); + + if (backing_file_blob) { + *backing_file_blobp = NULL; + kmem_cache_free(lsm_backing_file_cache, backing_file_blob); + } +} + /** * security_file_ioctl() - Check if an ioctl is allowed * @file: associated file @@ -2505,6 +2579,32 @@ int security_mmap_file(struct file *file, unsigned long prot, 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, 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 -- 2.53.0 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v3 1/2] lsm: add backing_file LSM hooks 2026-03-27 22:04 ` [PATCH v3 1/2] lsm: add backing_file LSM hooks Paul Moore @ 2026-03-28 8:29 ` Amir Goldstein 2026-03-28 16:34 ` Paul Moore 2026-03-30 8:35 ` Amir Goldstein 1 sibling, 1 reply; 7+ messages in thread From: Amir Goldstein @ 2026-03-28 8:29 UTC (permalink / raw) To: Paul Moore Cc: linux-security-module, selinux, linux-fsdevel, linux-unionfs, linux-erofs, Gao Xiang, Christian Brauner, Miklos Szeredi On Fri, Mar 27, 2026 at 11:05 PM Paul Moore <paul@paul-moore.com> wrote: > > 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 two other small changes to support these new LSM hooks. We > 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, and we 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 > Acked-by: Christian Brauner <brauner@kernel.org> > Signed-off-by: Paul Moore <paul@paul-moore.com> > --- I 100% agree with Christian. This is much better than my O_PATH file hack It is also what Miklos had initially suggested. I have a minor suggestion for API change though > fs/backing-file.c | 18 ++++-- > fs/erofs/ishare.c | 10 +++- > fs/file_table.c | 21 ++++++- > fs/fuse/passthrough.c | 2 +- > fs/internal.h | 3 +- > fs/overlayfs/dir.c | 2 +- > fs/overlayfs/file.c | 2 +- > include/linux/backing-file.h | 4 +- > include/linux/fs.h | 1 + > 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/lsm.h | 1 + > security/lsm_init.c | 9 +++ > security/security.c | 100 ++++++++++++++++++++++++++++++++++ > 16 files changed, 187 insertions(+), 16 deletions(-) > > diff --git a/fs/backing-file.c b/fs/backing-file.c > index 45da8600d564..1f3bbfc75882 100644 > --- a/fs/backing-file.c > +++ b/fs/backing-file.c > @@ -12,6 +12,7 @@ > #include <linux/backing-file.h> > #include <linux/splice.h> > #include <linux/mm.h> > +#include <linux/security.h> > > #include "internal.h" > > @@ -29,14 +30,15 @@ > * returned file into a container structure that also stores the stacked > * file's path, which can be retrieved using backing_file_user_path(). > */ > -struct file *backing_file_open(const struct path *user_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; > > @@ -52,15 +54,16 @@ struct file *backing_file_open(const struct path *user_path, int flags, > } > EXPORT_SYMBOL_GPL(backing_file_open); > > -struct file *backing_tmpfile_open(const struct path *user_path, int flags, > +struct file *backing_tmpfile_open(const struct file *user_file, int flags, > const struct path *real_parentpath, > umode_t mode, const struct cred *cred) > { > struct mnt_idmap *real_idmap = mnt_idmap(real_parentpath->mnt); > + 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; > > @@ -336,8 +339,13 @@ int backing_file_mmap(struct file *file, struct vm_area_struct *vma, > > vma_set_file(vma, file); > > - scoped_with_creds(ctx->cred) > + scoped_with_creds(ctx->cred) { > + ret = security_mmap_backing_file(vma, file, user_file); > + if (ret) > + return ret; > + > ret = vfs_mmap(vma->vm_file, vma); > + } > > if (ctx->accessed) > ctx->accessed(user_file); > diff --git a/fs/erofs/ishare.c b/fs/erofs/ishare.c > index 829d50d5c717..ec3fc5ac1a55 100644 > --- a/fs/erofs/ishare.c > +++ b/fs/erofs/ishare.c > @@ -4,6 +4,7 @@ > */ > #include <linux/xxhash.h> > #include <linux/mount.h> > +#include <linux/security.h> > #include "internal.h" > #include "xattr.h" > > @@ -106,7 +107,8 @@ static int erofs_ishare_file_open(struct inode *inode, struct file *file) > > if (file->f_flags & O_DIRECT) > return -EINVAL; > - realfile = alloc_empty_backing_file(O_RDONLY|O_NOATIME, current_cred()); > + realfile = alloc_empty_backing_file(O_RDONLY|O_NOATIME, current_cred(), > + file); > if (IS_ERR(realfile)) > return PTR_ERR(realfile); > ihold(sharedinode); > @@ -150,8 +152,14 @@ static ssize_t erofs_ishare_file_read_iter(struct kiocb *iocb, > static int erofs_ishare_mmap(struct file *file, struct vm_area_struct *vma) > { > struct file *realfile = file->private_data; > + int err; > > vma_set_file(vma, realfile); > + > + err = security_mmap_backing_file(vma, realfile, file); > + if (err) > + return err; > + > return generic_file_readonly_mmap(file, vma); > } > > diff --git a/fs/file_table.c b/fs/file_table.c > index aaa5faaace1e..0bdc26cae138 100644 > --- a/fs/file_table.c > +++ b/fs/file_table.c > @@ -50,6 +50,7 @@ struct backing_file { > struct path user_path; > freeptr_t bf_freeptr; > }; Shouldn't we wrap this with #ifdef CONFIG_SECURITY > + void *security; please initialize it in init_file() > }; > > #define backing_file(f) container_of(f, struct backing_file, file) > @@ -66,6 +67,11 @@ void backing_file_set_user_path(struct file *f, const struct path *path) > } > EXPORT_SYMBOL_GPL(backing_file_set_user_path); > > +void *backing_file_security(const struct file *f) > +{ > + return backing_file(f)->security; I think LSM code should be completely responsible for this ptr assignment/free so you should export void **backing_file_security_ptr(const struct file *f) { return &backing_file(f)->security; } > + > static inline void file_free(struct file *f) > { > security_file_free(f); > @@ -73,8 +79,11 @@ static inline void file_free(struct file *f) > percpu_counter_dec(&nr_files); > put_cred(f->f_cred); > if (unlikely(f->f_mode & FMODE_BACKING)) { > - path_put(backing_file_user_path(f)); > - kmem_cache_free(bfilp_cachep, backing_file(f)); > + struct backing_file *ff = backing_file(f); > + > + security_backing_file_free(&ff->security); Why do you need to add this in vfs code? Can't you do the same in security_file_free(f)? if (unlikely(f->f_mode & FMODE_BACKING)) security_backing_file_free(backing_file_security_ptr(f)); > + path_put(&ff->user_path); > + kmem_cache_free(bfilp_cachep, ff); > } else { > kmem_cache_free(filp_cachep, f); > } > @@ -290,7 +299,8 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred) > * 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; > @@ -306,6 +316,11 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred) > } > > ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT; > + error = security_backing_file_alloc(&ff->security, user_file);> + if (unlikely(error)) { > + fput(&ff->file); > + return ERR_PTR(error); > + } > return &ff->file; > } > EXPORT_SYMBOL_GPL(alloc_empty_backing_file); Maybe, and I am not sure, alloc_empty_backing_file() should call ONLY error = security_backing_file_alloc(&ff->file, user_file); Instead of security_file_alloc() AND security_backing_file_alloc() and security_backing_file_alloc() can make use of backing_file_security_ptr() accessor internally? I think this will further abstract LSM implementation details from vfs and avoid the need to spray #ifdef SECURITY in vfs code. WDYT? Thanks for following through with this elegant and clean API! Amir. ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3 1/2] lsm: add backing_file LSM hooks 2026-03-28 8:29 ` Amir Goldstein @ 2026-03-28 16:34 ` Paul Moore 0 siblings, 0 replies; 7+ messages in thread From: Paul Moore @ 2026-03-28 16:34 UTC (permalink / raw) To: Amir Goldstein Cc: linux-security-module, selinux, linux-fsdevel, linux-unionfs, linux-erofs, Gao Xiang, Christian Brauner, Miklos Szeredi On Sat, Mar 28, 2026 at 4:29 AM Amir Goldstein <amir73il@gmail.com> wrote: > On Fri, Mar 27, 2026 at 11:05 PM Paul Moore <paul@paul-moore.com> wrote: > > > > 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 two other small changes to support these new LSM hooks. We > > 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, and we 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 > > Acked-by: Christian Brauner <brauner@kernel.org> > > Signed-off-by: Paul Moore <paul@paul-moore.com> > > --- > > I 100% agree with Christian. > This is much better than my O_PATH file hack I'm not surprised that both you and Christian prefer this solution, it moves all the pain of resolving this issue to the individual LSMs. Just look at how the SELinux code has changed, even trying to pretty it up as best as possible, it's objectively much uglier now, not to mention more complicated. From my perspective the root cause of this issue lies in the overlayfs/backing-file design, specifically how overlayfs hides multiple files under a single file so that it can plug into the existing VFS/userspace paradigm of a single file. While the design and abstraction are no doubt very clever things, and for the most part they "just work", there are definitely some corner cases that require special handling, e.g. LSM access controls around mprotect(). In my opinion, the burden of hiding any ugliness associated with this special handling lies with the subsystem implementing the abstraction, which is why I was pushing for a solution where the VFS and/or backing-file layer would provide the user file (or a stand-in) for the LSMs to use. Unfortunately, that was not something the overlayfs and VFS communities were willing to tolerate, so those of us in the LSM space were left with a terrible choice: accept that the overlayfs/VFS folks don't care and hack around the shortcomings of overlayfs, or leave a public vulnerability for an unknown period of time while the overlayfs/VFS folks argue over a solution, with the a non-trivial chance that the LSMs would need to hack around the problem anyway. That's my view of were things were at, and why I begrudgingly took this approach. I'm sure you have your own perspecitve, and I'm not going to be surprised if you view this primarily as a LSM problem; it's a common viewpoint amongst Linux kernel maintainers not responsible for a LSM. > It is also what Miklos had initially suggested. Perhaps I've lost the mail, but going back to when this issue was first discovered, I don't see anything from Miklos relating to this in either my inbox or the mailing lists. > > diff --git a/fs/file_table.c b/fs/file_table.c > > index aaa5faaace1e..0bdc26cae138 100644 > > --- a/fs/file_table.c > > +++ b/fs/file_table.c > > @@ -50,6 +50,7 @@ struct backing_file { > > struct path user_path; > > freeptr_t bf_freeptr; > > }; > > Shouldn't we wrap this with > #ifdef CONFIG_SECURITY Sure, I'll change that. > > + void *security; > > please initialize it in init_file() We lack a clean way to access the backing_file struct in init_file(). I placed the security_backing_file_alloc() initializer in alloc_empty_backing_file() as it was the first place where we could both allocate the necessary LSM blob and initialize it with the data from the user file at the same time. If you want to intialize backing_file->security in init_file(), init_file() we will need to add a FMODE_BACKING check in init_file and split the security_backing_file_alloc() hook into two: one in init_file() to do the allocation and basic init, one in alloc_empty_backing_file() to capture the necessary user file data. Do you still prefer to move the backing_file->security initializtion into init_file()? > > +void *backing_file_security(const struct file *f) > > +{ > > + return backing_file(f)->security; > > I think LSM code should be completely responsible for this ptr > assignment/free so you should export > > void **backing_file_security_ptr(const struct file *f) > { > return &backing_file(f)->security; > } Doing so would require us to also move the backing_file struct definition into include/linux/backing-file.h (or similar), which I tried very hard to avoid as I suspected you would not approve of that. I figured if you had wanted to expose the struct definition you would have defined it in backing-file.h as opposed to file_table.c. Would you like me to move the backing_file struct definition into include/linux/backing-file.h? > > @@ -73,8 +79,11 @@ static inline void file_free(struct file *f) > > percpu_counter_dec(&nr_files); > > put_cred(f->f_cred); > > if (unlikely(f->f_mode & FMODE_BACKING)) { > > - path_put(backing_file_user_path(f)); > > - kmem_cache_free(bfilp_cachep, backing_file(f)); > > + struct backing_file *ff = backing_file(f); > > + > > + security_backing_file_free(&ff->security); > > Why do you need to add this in vfs code? > > Can't you do the same in security_file_free(f)? > if (unlikely(f->f_mode & FMODE_BACKING)) > security_backing_file_free(backing_file_security_ptr(f)); See my comments above regarding the visibility of the backing_file struct. > > + path_put(&ff->user_path); > > + kmem_cache_free(bfilp_cachep, ff); > > } else { > > kmem_cache_free(filp_cachep, f); > > } > > @@ -290,7 +299,8 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred) > > * 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; > > @@ -306,6 +316,11 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred) > > } > > > > ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT; > > + error = security_backing_file_alloc(&ff->security, user_file);> + if (unlikely(error)) { > > + fput(&ff->file); > > + return ERR_PTR(error); > > + } > > return &ff->file; > > } > > EXPORT_SYMBOL_GPL(alloc_empty_backing_file); > > Maybe, and I am not sure, > alloc_empty_backing_file() should call ONLY > error = security_backing_file_alloc(&ff->file, user_file); > > Instead of security_file_alloc() AND security_backing_file_alloc() > and security_backing_file_alloc() can make use of > backing_file_security_ptr() accessor internally? This is another case of the code being structured so that we don't need to expose the backing_file struct definition to the LSMs. If you would prefer to expose the backing_file struct in include/linux I can probably make a few additional simplifications to the code. -- paul-moore.com ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v3 1/2] lsm: add backing_file LSM hooks 2026-03-27 22:04 ` [PATCH v3 1/2] lsm: add backing_file LSM hooks Paul Moore 2026-03-28 8:29 ` Amir Goldstein @ 2026-03-30 8:35 ` Amir Goldstein 2026-03-31 2:13 ` Paul Moore 1 sibling, 1 reply; 7+ messages in thread From: Amir Goldstein @ 2026-03-30 8:35 UTC (permalink / raw) To: Paul Moore Cc: linux-security-module, selinux, linux-fsdevel, linux-unionfs, linux-erofs, Gao Xiang, Christian Brauner [-- Attachment #1: Type: text/plain, Size: 6230 bytes --] On Fri, Mar 27, 2026 at 11:05 PM Paul Moore <paul@paul-moore.com> wrote: > > 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 two other small changes to support these new LSM hooks. We > 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, and we 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 > Acked-by: Christian Brauner <brauner@kernel.org> > Signed-off-by: Paul Moore <paul@paul-moore.com> > --- > fs/backing-file.c | 18 ++++-- > fs/erofs/ishare.c | 10 +++- > fs/file_table.c | 21 ++++++- > fs/fuse/passthrough.c | 2 +- > fs/internal.h | 3 +- > fs/overlayfs/dir.c | 2 +- > fs/overlayfs/file.c | 2 +- > include/linux/backing-file.h | 4 +- > include/linux/fs.h | 1 + > 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/lsm.h | 1 + > security/lsm_init.c | 9 +++ > security/security.c | 100 ++++++++++++++++++++++++++++++++++ > 16 files changed, 187 insertions(+), 16 deletions(-) > That looks like a nice clean abstraction to me. ... > diff --git a/fs/file_table.c b/fs/file_table.c > index aaa5faaace1e..0bdc26cae138 100644 > --- a/fs/file_table.c > +++ b/fs/file_table.c > @@ -50,6 +50,7 @@ struct backing_file { > struct path user_path; > freeptr_t bf_freeptr; > }; > + void *security; This needs ifdef SECURITY and the name should be user_security > }; > > #define backing_file(f) container_of(f, struct backing_file, file) > @@ -66,6 +67,11 @@ void backing_file_set_user_path(struct file *f, const struct path *path) > } > EXPORT_SYMBOL_GPL(backing_file_set_user_path); > > +void *backing_file_security(const struct file *f) > +{ > + return backing_file(f)->security; > +} I prefer the name backing_file_user_security() Terminology here is very confusing but when saying "backing file" it is more natural that one is referring to the backing xfs file with overlayfs has opened. The "backing file" already has an LSM blob f->f_security which is fair the call it the "backing file's LSM blob" Therefore, I think we need to make a distinction, as we did with backing_file_user_path() and refer to this as something along the lines of the "backing file's user LSM blob". > + > static inline void file_free(struct file *f) > { > security_file_free(f); > @@ -73,8 +79,11 @@ static inline void file_free(struct file *f) > percpu_counter_dec(&nr_files); > put_cred(f->f_cred); > if (unlikely(f->f_mode & FMODE_BACKING)) { > - path_put(backing_file_user_path(f)); > - kmem_cache_free(bfilp_cachep, backing_file(f)); > + struct backing_file *ff = backing_file(f); > + > + security_backing_file_free(&ff->security); > + path_put(&ff->user_path); > + kmem_cache_free(bfilp_cachep, ff); Not directly related to your patch, but as this is growing, IMO this would look cleaner with backing_file_free() inline helper (see attached path). > } else { > kmem_cache_free(filp_cachep, f); > } > @@ -290,7 +299,8 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred) > * 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; > @@ -306,6 +316,11 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred) > } > > ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT; > + error = security_backing_file_alloc(&ff->security, user_file); > + if (unlikely(error)) { > + fput(&ff->file); > + return ERR_PTR(error); > + } > return &ff->file; > } There is an API issue here. in order to call fput() we must ensure that user_security was initialized to NULL (or allocated). I don't think that we want security_backing_file_alloc() to provide this semantic and the current patch does not implement it. Furthermore, user_path is also not initialized in the error case. Attached UNTESTED fixup patch to suggest a cleanup with init_backing_file() helper. It also changes the variable and helper name to user_security and plays some trick to avoid many ifdef SECURITY. Feel free to take whichever bits you like with/without attribution. If you prefer, attached also a proper prep patch. compile tested only. Thanks, Amir. [-- Attachment #2: 0001-backing_file_user_security.patch --] [-- Type: text/x-patch, Size: 3765 bytes --] From 4858f610d960454ab4de0f29f3557016e80848bd Mon Sep 17 00:00:00 2001 From: Amir Goldstein <amir73il@gmail.com> Date: Mon, 30 Mar 2026 08:26:01 +0200 Subject: [PATCH] backing_file_user_security --- fs/file_table.c | 47 ++++++++++++++++++++++++++++++++++++---------- include/linux/fs.h | 2 +- 2 files changed, 38 insertions(+), 11 deletions(-) diff --git a/fs/file_table.c b/fs/file_table.c index 0bdc26cae1389..4666e88ba687d 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -43,14 +43,19 @@ static struct kmem_cache *bfilp_cachep __ro_after_init; static struct percpu_counter nr_files __cacheline_aligned_in_smp; -/* Container for backing file with optional user path */ +/* Container for backing file with optional user path and security blob */ struct backing_file { struct file file; union { struct path user_path; freeptr_t bf_freeptr; + void *dummy_security; }; - void *security; +#ifdef CONFIG_SECURITY + void *user_security; +#else +#define user_security dummy_security +#endif }; #define backing_file(f) container_of(f, struct backing_file, file) @@ -67,9 +72,16 @@ void backing_file_set_user_path(struct file *f, const struct path *path) } EXPORT_SYMBOL_GPL(backing_file_set_user_path); -void *backing_file_security(const struct file *f) +void *backing_file_user_security(struct file *f) { - return backing_file(f)->security; + return backing_file(f)->user_security; +} + +static inline void backing_file_free(struct backing_file *ff) +{ + security_backing_file_free(&ff->user_security); + path_put(&ff->user_path); + kmem_cache_free(bfilp_cachep, ff); } static inline void file_free(struct file *f) @@ -79,11 +91,7 @@ static inline void file_free(struct file *f) percpu_counter_dec(&nr_files); put_cred(f->f_cred); if (unlikely(f->f_mode & FMODE_BACKING)) { - struct backing_file *ff = backing_file(f); - - security_backing_file_free(&ff->security); - path_put(&ff->user_path); - kmem_cache_free(bfilp_cachep, ff); + backing_file_free(backing_file(f)); } else { kmem_cache_free(filp_cachep, f); } @@ -292,6 +300,23 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred) return f; } +static int init_backing_file(struct backing_file *ff, + const struct file *user_file) +{ + int error; + + memset(&ff->user_path, 0, sizeof(ff->user_path)); + ff->user_security = NULL; + + error = security_backing_file_alloc(&ff->user_security, user_file); + if (unlikely(error)) { + fput(&ff->file); + return ERR_PTR(error); + } + + return 0; +} + /* * Variant of alloc_empty_file() that allocates a backing_file container * and doesn't check and modify nr_files. @@ -315,12 +340,14 @@ 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 = security_backing_file_alloc(&ff->security, user_file); + error = init_backing_file(ff, user_file); if (unlikely(error)) { fput(&ff->file); return ERR_PTR(error); } + return &ff->file; } EXPORT_SYMBOL_GPL(alloc_empty_backing_file); diff --git a/include/linux/fs.h b/include/linux/fs.h index 8f5702cfb5e0b..60450a0790add 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2474,7 +2474,7 @@ struct file *dentry_open_nonotify(const struct path *path, int flags, struct file *dentry_create(struct path *path, int flags, umode_t mode, const struct cred *cred); const struct path *backing_file_user_path(const struct file *f); -void *backing_file_security(const struct file *f); +void *backing_file_user_security(const struct file *f); /* * When mmapping a file on a stackable filesystem (e.g., overlayfs), the file -- 2.53.0 [-- Attachment #3: 0001-fs-prepare-for-adding-user_security-block-to-backing.patch --] [-- Type: text/x-patch, Size: 2128 bytes --] From cad1df280bcc935289c787f5f4deb4a23ea20fcd Mon Sep 17 00:00:00 2001 From: Amir Goldstein <amir73il@gmail.com> Date: Mon, 30 Mar 2026 10:27:51 +0200 Subject: [PATCH] fs: prepare for adding user_security block to backing_file In preparation to adding user_security blob to backing_file struct, factor out helpers init_backing_file() and backing_file_free(). Signed-off-by: Amir Goldstein <amir73il@gmail.com> --- fs/file_table.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/fs/file_table.c b/fs/file_table.c index aaa5faaace1e9..9e02c1f16db3c 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -66,6 +66,12 @@ void backing_file_set_user_path(struct file *f, const struct path *path) } EXPORT_SYMBOL_GPL(backing_file_set_user_path); +static inline void backing_file_free(struct backing_file *ff) +{ + path_put(&ff->user_path); + kmem_cache_free(bfilp_cachep, ff); +} + static inline void file_free(struct file *f) { security_file_free(f); @@ -73,8 +79,7 @@ static inline void file_free(struct file *f) percpu_counter_dec(&nr_files); put_cred(f->f_cred); if (unlikely(f->f_mode & FMODE_BACKING)) { - path_put(backing_file_user_path(f)); - kmem_cache_free(bfilp_cachep, backing_file(f)); + backing_file_free(backing_file(f)); } else { kmem_cache_free(filp_cachep, f); } @@ -283,6 +288,12 @@ 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->user_path, 0, sizeof(ff->user_path)); + return 0; +} + /* * Variant of alloc_empty_file() that allocates a backing_file container * and doesn't check and modify nr_files. @@ -305,7 +316,14 @@ 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; } EXPORT_SYMBOL_GPL(alloc_empty_backing_file); -- 2.53.0 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v3 1/2] lsm: add backing_file LSM hooks 2026-03-30 8:35 ` Amir Goldstein @ 2026-03-31 2:13 ` Paul Moore 0 siblings, 0 replies; 7+ messages in thread From: Paul Moore @ 2026-03-31 2:13 UTC (permalink / raw) To: Amir Goldstein Cc: linux-security-module, selinux, linux-fsdevel, linux-unionfs, linux-erofs, Gao Xiang, Christian Brauner On Mon, Mar 30, 2026 at 4:35 AM Amir Goldstein <amir73il@gmail.com> wrote: > On Fri, Mar 27, 2026 at 11:05 PM Paul Moore <paul@paul-moore.com> wrote: > > > > 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 ... ... > > diff --git a/fs/file_table.c b/fs/file_table.c > > index aaa5faaace1e..0bdc26cae138 100644 > > --- a/fs/file_table.c > > +++ b/fs/file_table.c > > @@ -50,6 +50,7 @@ struct backing_file { > > struct path user_path; > > freeptr_t bf_freeptr; > > }; > > + void *security; > > This needs ifdef SECURITY Yep. That will require some other changes, but I should be able to keep those fairly limited. > and the name should be user_security I'd strongly prefer to keep it as "security" both because "void *security" is a very common pattern in the kernel when adding LSM blobs to structs, and we don't know what each and every LSM may need to store in the backing_file LSM blob. > > +void *backing_file_security(const struct file *f) > > +{ > > + return backing_file(f)->security; > > +} > > I prefer the name backing_file_user_security() > > Terminology here is very confusing but when saying > "backing file" it is more natural that one is referring to the > backing xfs file with overlayfs has opened. > > The "backing file" already has an LSM blob f->f_security > which is fair the call it the "backing file's LSM blob" ... From a LSM dev's perspective, I would call file->f_security blob a file's LSM blob regardless of if the file is a user or backing file; the backing_file->security blob would be a backing file LSM blob. If you look at what the SELinux code does, specifically in the __file_has_perm() and __file_map_prot_check() functions (newly added in this patchset), you'll see this supported by the code: the file->f_security field is basically handled the same regardless of if it is a user or backing file whereas the backing_file->security field is handled very differently because it is a backing file. While I think it makes sense to match the accessor function's name to the struct field, ultimately I care more about the struct field's name. If you really feel strongly about changing backing_file_security() to backing_file_user_security() I can live with that so long as we keep backing_file->security intact. > > @@ -73,8 +79,11 @@ static inline void file_free(struct file *f) > > percpu_counter_dec(&nr_files); > > put_cred(f->f_cred); > > if (unlikely(f->f_mode & FMODE_BACKING)) { > > - path_put(backing_file_user_path(f)); > > - kmem_cache_free(bfilp_cachep, backing_file(f)); > > + struct backing_file *ff = backing_file(f); > > + > > + security_backing_file_free(&ff->security); > > + path_put(&ff->user_path); > > + kmem_cache_free(bfilp_cachep, ff); > > Not directly related to your patch, but as this is growing, IMO > this would look cleaner with backing_file_free() inline helper > (see attached path). Sure, I'll include your patch in the patchset. I'll also fix the comment style in the patch to match C style in the rest of the file (I'll note the change in the metadata). > > } else { > > kmem_cache_free(filp_cachep, f); > > } > > @@ -290,7 +299,8 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred) > > * 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; > > @@ -306,6 +316,11 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred) > > } > > > > ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT; > > + error = security_backing_file_alloc(&ff->security, user_file); > > + if (unlikely(error)) { > > + fput(&ff->file); > > + return ERR_PTR(error); > > + } > > return &ff->file; > > } > > There is an API issue here. > in order to call fput() we must ensure that user_security was initialized to > NULL (or allocated). > > I don't think that we want security_backing_file_alloc() to provide this > semantic and the current patch does not implement it. > > Furthermore, user_path is also not initialized in the error case. > > Attached UNTESTED fixup patch to suggest a cleanup with > init_backing_file() helper. > > It also changes the variable and helper name to user_security > and plays some trick to avoid many ifdef SECURITY. > Feel free to take whichever bits you like with/without attribution. I think I've got a cleaner approach than what you've proposed, let me code it up, test it all, and I'll post a new revision of the patchset soon. -- paul-moore.com ^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v3 2/2] selinux: fix overlayfs mmap() and mprotect() access checks 2026-03-27 22:04 [PATCH v3 0/2] Fix incorrect overlayfs mmap() and mprotect() LSM access controls Paul Moore 2026-03-27 22:04 ` [PATCH v3 1/2] lsm: add backing_file LSM hooks Paul Moore @ 2026-03-27 22:04 ` Paul Moore 1 sibling, 0 replies; 7+ messages in thread From: Paul Moore @ 2026-03-27 22:04 UTC (permalink / raw) To: linux-security-module, selinux, linux-fsdevel, linux-unionfs, linux-erofs Cc: Amir Goldstein, Gao Xiang, Christian Brauner 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 Signed-off-by: Paul Moore <paul@paul-moore.com> --- security/selinux/hooks.c | 256 +++++++++++++++++++++--------- security/selinux/include/objsec.h | 17 ++ 2 files changed, 202 insertions(+), 71 deletions(-) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index d8224ea113d1..d8557da79480 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -1745,6 +1745,60 @@ static inline int file_path_has_perm(const struct cred *cred, static int bpf_fd_pass(const struct file *file, u32 sid); #endif +static int __file_has_perm(const struct cred *cred, const struct file *file, + u32 av, bool bf_user_file) + +{ + struct common_audit_data ad; + struct inode *inode; + u32 ssid = cred_sid(cred); + u32 tsid_fd; + int rc; + + if (bf_user_file) { + struct backing_file_security_struct *bfsec; + const struct path *path; + + if (WARN_ON(!(file->f_mode & FMODE_BACKING))) + return -EIO; + + bfsec = selinux_backing_file(file); + path = backing_file_user_path(file); + 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) + return rc; + } + +#ifdef CONFIG_BPF_SYSCALL + /* 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. */ + if (av) + return inode_has_perm(cred, inode, av, &ad); + + 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 @@ -1753,41 +1807,10 @@ static int bpf_fd_pass(const struct file *file, u32 sid); 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 inline int file_has_perm(const struct cred *cred, + const struct file *file, u32 av) { - struct file_security_struct *fsec = selinux_file(file); - struct inode *inode = file_inode(file); - struct common_audit_data ad; - u32 sid = cred_sid(cred); - int rc; - - ad.type = LSM_AUDIT_DATA_FILE; - ad.u.file = file; - - if (sid != fsec->sid) { - rc = avc_has_perm(sid, fsec->sid, - SECCLASS_FD, - FD__USE, - &ad); - if (rc) - goto out; - } - -#ifdef CONFIG_BPF_SYSCALL - rc = bpf_fd_pass(file, cred_sid(cred)); - 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); - -out: - return rc; + return __file_has_perm(cred, file, av, false); } /* @@ -3825,6 +3848,17 @@ static int selinux_file_alloc_security(struct file *file) return 0; } +static int selinux_backing_file_alloc(void *backing_file_blob, + const struct file *user_file) +{ + struct backing_file_security_struct *bfsec; + + bfsec = selinux_backing_file_raw(backing_file_blob); + bfsec->uf_sid = selinux_file(user_file)->sid; + + return 0; +} + /* * Check whether a task has the ioctl permission and cmd * operation to an inode. @@ -3942,42 +3976,55 @@ 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(backing_file_user_path(file)->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) @@ -3993,36 +4040,80 @@ 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 @@ -4036,11 +4127,15 @@ 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 @@ -4048,13 +4143,29 @@ 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) @@ -7393,6 +7504,7 @@ struct lsm_blob_sizes selinux_blob_sizes __ro_after_init = { .lbs_cred = sizeof(struct cred_security_struct), .lbs_task = 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_key = sizeof(struct key_security_struct), @@ -7498,9 +7610,11 @@ 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 5bddd28ea5cb..8ec493064aa2 100644 --- a/security/selinux/include/objsec.h +++ b/security/selinux/include/objsec.h @@ -88,6 +88,10 @@ 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 */ @@ -195,6 +199,19 @@ 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_raw(void *blob) +{ + return blob + selinux_blob_sizes.lbs_backing_file; +} + +static inline struct backing_file_security_struct * +selinux_backing_file(const struct file *backing_file) +{ + void *blob = backing_file_security(backing_file); + return selinux_backing_file_raw(blob); +} + static inline struct inode_security_struct * selinux_inode(const struct inode *inode) { -- 2.53.0 ^ permalink raw reply related [flat|nested] 7+ messages in thread
end of thread, other threads:[~2026-03-31 2:14 UTC | newest] Thread overview: 7+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2026-03-27 22:04 [PATCH v3 0/2] Fix incorrect overlayfs mmap() and mprotect() LSM access controls Paul Moore 2026-03-27 22:04 ` [PATCH v3 1/2] lsm: add backing_file LSM hooks Paul Moore 2026-03-28 8:29 ` Amir Goldstein 2026-03-28 16:34 ` Paul Moore 2026-03-30 8:35 ` Amir Goldstein 2026-03-31 2:13 ` Paul Moore 2026-03-27 22:04 ` [PATCH v3 2/2] selinux: fix overlayfs mmap() and mprotect() access checks Paul Moore
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