[PATCH v2] bpf: have bpf_real_data_inode() take a struct file

[PATCH v2] bpf: have bpf_real_data_inode() take a struct file

[Christian Brauner]

bpf_real_data_inode() must be usable from the bprm_check_security,
mmap_file and file_mprotect hooks for systemd's RestrictFilesystemAccess
BPF LSM program, so have it take a struct file instead of a dentry.

Amir Goldstein <amir73il@gmail.com> suggests:

  While doing so, rename it from bpf_real_inode() to
  bpf_real_data_inode(). For a regular file on a union/overlay
  filesystem it resolves to the underlying inode that hosts the data,
  but for a non-regular file it returns the overlay inode. The new name
  makes the "inode hosting the data" intent explicit and avoids the
  ambiguity of "the real inode backing a file". Document the
  non-regular-file behavior in the kfunc too.

Both the signature change and the rename are safe because the kfunc
landed this cycle and has no released users.

Fixes: 9af8c8a54f6e ("bpf: add bpf_real_inode() kfunc")
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
Changes in v2:
- Rename bpf_real_inode() -> bpf_real_data_inode() (Amir); the new name
  makes the "inode hosting the data" intent explicit.
- Document that the kfunc returns the overlay inode for non-regular files.
- Link to v1: https://patch.msgid.link/20260622-work-bpf-real_inode-v1-1-4014eb4cbefd@kernel.org
---
 fs/bpf_fs_kfuncs.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
index 768aca2dc0f0..f1863a891db6 100644
--- a/fs/bpf_fs_kfuncs.c
+++ b/fs/bpf_fs_kfuncs.c
@@ -360,18 +360,23 @@ __bpf_kfunc int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__s
 #endif /* CONFIG_CGROUPS */
 
 /**
- * bpf_real_inode - get the real inode backing a dentry
- * @dentry: dentry to resolve
+ * bpf_real_data_inode - get the real inode hosting a file's data
+ * @file: file to resolve
  *
- * If the dentry is on a union/overlay filesystem, return the underlying, real
- * inode that hosts the data.  Otherwise return the inode attached to the
- * dentry itself.
+ * Resolve @file to the inode that hosts its data. For a regular file on a
+ * union/overlay filesystem this is the underlying (upper or lower) inode that
+ * stores the data, not the overlay inode.
  *
- * Return: The real inode backing the dentry, or NULL for a negative dentry.
+ * Data resolution only applies to regular files. For a non-regular file (e.g.
+ * a device node, fifo or socket) on a union/overlay filesystem the overlay
+ * inode itself is returned; for any file on a non-union filesystem the inode
+ * attached to @file is returned.
+ *
+ * Return: The inode hosting @file's data, or NULL.
  */
-__bpf_kfunc struct inode *bpf_real_inode(struct dentry *dentry)
+__bpf_kfunc struct inode *bpf_real_data_inode(struct file *file)
 {
-	return d_real_inode(dentry);
+	return d_real_inode(file_dentry(file));
 }
 
 __bpf_kfunc_end_defs();
@@ -384,7 +389,7 @@ BTF_ID_FLAGS(func, bpf_get_dentry_xattr, KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_set_dentry_xattr, KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_remove_dentry_xattr, KF_SLEEPABLE)
-BTF_ID_FLAGS(func, bpf_real_inode, KF_SLEEPABLE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_real_data_inode, KF_SLEEPABLE | KF_RET_NULL)
 BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)
 
 static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)

---
base-commit: 5b33fc6492a7b7a62359157db0f92f5b6e9af690
change-id: 20260622-work-bpf-real_inode-c3202dbaf0ab

Re: [PATCH v2] bpf: have bpf_real_data_inode() take a struct file

[Amir Goldstein]

On Tue, Jun 23, 2026 at 11:32 AM Christian Brauner <brauner@kernel.org> wrote:
>
> bpf_real_data_inode() must be usable from the bprm_check_security,
> mmap_file and file_mprotect hooks for systemd's RestrictFilesystemAccess
> BPF LSM program, so have it take a struct file instead of a dentry.
>
> Amir Goldstein <amir73il@gmail.com> suggests:
>
>   While doing so, rename it from bpf_real_inode() to
>   bpf_real_data_inode(). For a regular file on a union/overlay
>   filesystem it resolves to the underlying inode that hosts the data,
>   but for a non-regular file it returns the overlay inode. The new name
>   makes the "inode hosting the data" intent explicit and avoids the
>   ambiguity of "the real inode backing a file". Document the
>   non-regular-file behavior in the kfunc too.
>
> Both the signature change and the rename are safe because the kfunc
> landed this cycle and has no released users.
>
> Fixes: 9af8c8a54f6e ("bpf: add bpf_real_inode() kfunc")
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

> ---
> Changes in v2:
> - Rename bpf_real_inode() -> bpf_real_data_inode() (Amir); the new name
>   makes the "inode hosting the data" intent explicit.
> - Document that the kfunc returns the overlay inode for non-regular files.
> - Link to v1: https://patch.msgid.link/20260622-work-bpf-real_inode-v1-1-4014eb4cbefd@kernel.org
> ---
>  fs/bpf_fs_kfuncs.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> index 768aca2dc0f0..f1863a891db6 100644
> --- a/fs/bpf_fs_kfuncs.c
> +++ b/fs/bpf_fs_kfuncs.c
> @@ -360,18 +360,23 @@ __bpf_kfunc int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__s
>  #endif /* CONFIG_CGROUPS */
>
>  /**
> - * bpf_real_inode - get the real inode backing a dentry
> - * @dentry: dentry to resolve
> + * bpf_real_data_inode - get the real inode hosting a file's data
> + * @file: file to resolve
>   *
> - * If the dentry is on a union/overlay filesystem, return the underlying, real
> - * inode that hosts the data.  Otherwise return the inode attached to the
> - * dentry itself.
> + * Resolve @file to the inode that hosts its data. For a regular file on a
> + * union/overlay filesystem this is the underlying (upper or lower) inode that
> + * stores the data, not the overlay inode.
>   *
> - * Return: The real inode backing the dentry, or NULL for a negative dentry.
> + * Data resolution only applies to regular files. For a non-regular file (e.g.
> + * a device node, fifo or socket) on a union/overlay filesystem the overlay
> + * inode itself is returned; for any file on a non-union filesystem the inode
> + * attached to @file is returned.
> + *
> + * Return: The inode hosting @file's data, or NULL.
>   */
> -__bpf_kfunc struct inode *bpf_real_inode(struct dentry *dentry)
> +__bpf_kfunc struct inode *bpf_real_data_inode(struct file *file)
>  {
> -       return d_real_inode(dentry);
> +       return d_real_inode(file_dentry(file));
>  }
>
>  __bpf_kfunc_end_defs();
> @@ -384,7 +389,7 @@ BTF_ID_FLAGS(func, bpf_get_dentry_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_set_dentry_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_remove_dentry_xattr, KF_SLEEPABLE)
> -BTF_ID_FLAGS(func, bpf_real_inode, KF_SLEEPABLE | KF_RET_NULL)
> +BTF_ID_FLAGS(func, bpf_real_data_inode, KF_SLEEPABLE | KF_RET_NULL)
>  BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)
>
>  static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
>
> ---
> base-commit: 5b33fc6492a7b7a62359157db0f92f5b6e9af690
> change-id: 20260622-work-bpf-real_inode-c3202dbaf0ab
>

Re: [PATCH v2] bpf: have bpf_real_data_inode() take a struct file

[Christian Brauner]

On Tue, 23 Jun 2026 11:32:27 +0200, Christian Brauner wrote:
> bpf: have bpf_real_data_inode() take a struct file

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] bpf: have bpf_real_data_inode() take a struct file
      https://git.kernel.org/vfs/vfs/c/c99895a8cbee

Re: [PATCH v2] bpf: have bpf_real_data_inode() take a struct file

[Emil Tsalapatis]

On Tue Jun 23, 2026 at 5:32 AM EDT, Christian Brauner wrote:
> bpf_real_data_inode() must be usable from the bprm_check_security,
> mmap_file and file_mprotect hooks for systemd's RestrictFilesystemAccess
> BPF LSM program, so have it take a struct file instead of a dentry.
>
> Amir Goldstein <amir73il@gmail.com> suggests:
>
>   While doing so, rename it from bpf_real_inode() to
>   bpf_real_data_inode(). For a regular file on a union/overlay
>   filesystem it resolves to the underlying inode that hosts the data,
>   but for a non-regular file it returns the overlay inode. The new name
>   makes the "inode hosting the data" intent explicit and avoids the
>   ambiguity of "the real inode backing a file". Document the
>   non-regular-file behavior in the kfunc too.
>
> Both the signature change and the rename are safe because the kfunc
> landed this cycle and has no released users.
>
> Fixes: 9af8c8a54f6e ("bpf: add bpf_real_inode() kfunc")
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>

> ---
> Changes in v2:
> - Rename bpf_real_inode() -> bpf_real_data_inode() (Amir); the new name
>   makes the "inode hosting the data" intent explicit.
> - Document that the kfunc returns the overlay inode for non-regular files.
> - Link to v1: https://patch.msgid.link/20260622-work-bpf-real_inode-v1-1-4014eb4cbefd@kernel.org
> ---
>  fs/bpf_fs_kfuncs.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> index 768aca2dc0f0..f1863a891db6 100644
> --- a/fs/bpf_fs_kfuncs.c
> +++ b/fs/bpf_fs_kfuncs.c
> @@ -360,18 +360,23 @@ __bpf_kfunc int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__s
>  #endif /* CONFIG_CGROUPS */
>  
>  /**
> - * bpf_real_inode - get the real inode backing a dentry
> - * @dentry: dentry to resolve
> + * bpf_real_data_inode - get the real inode hosting a file's data
> + * @file: file to resolve
>   *
> - * If the dentry is on a union/overlay filesystem, return the underlying, real
> - * inode that hosts the data.  Otherwise return the inode attached to the
> - * dentry itself.
> + * Resolve @file to the inode that hosts its data. For a regular file on a
> + * union/overlay filesystem this is the underlying (upper or lower) inode that
> + * stores the data, not the overlay inode.
>   *
> - * Return: The real inode backing the dentry, or NULL for a negative dentry.
> + * Data resolution only applies to regular files. For a non-regular file (e.g.
> + * a device node, fifo or socket) on a union/overlay filesystem the overlay
> + * inode itself is returned; for any file on a non-union filesystem the inode
> + * attached to @file is returned.
> + *
> + * Return: The inode hosting @file's data, or NULL.
>   */
> -__bpf_kfunc struct inode *bpf_real_inode(struct dentry *dentry)
> +__bpf_kfunc struct inode *bpf_real_data_inode(struct file *file)
>  {
> -	return d_real_inode(dentry);
> +	return d_real_inode(file_dentry(file));
>  }
>  
>  __bpf_kfunc_end_defs();
> @@ -384,7 +389,7 @@ BTF_ID_FLAGS(func, bpf_get_dentry_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_set_dentry_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_remove_dentry_xattr, KF_SLEEPABLE)
> -BTF_ID_FLAGS(func, bpf_real_inode, KF_SLEEPABLE | KF_RET_NULL)
> +BTF_ID_FLAGS(func, bpf_real_data_inode, KF_SLEEPABLE | KF_RET_NULL)
>  BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)
>  
>  static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
>
> ---
> base-commit: 5b33fc6492a7b7a62359157db0f92f5b6e9af690
> change-id: 20260622-work-bpf-real_inode-c3202dbaf0ab