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bpf: have bpf_real_data_inode() take a struct file

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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.

Link: https://patch.msgid.link/20260623-work-bpf-real_inode-v2-1-8e8b57dd25f7@kernel.org
Fixes: 9af8c8a54f ("bpf: add bpf_real_inode() kfunc")
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2026-06-23 11:32:27 +02:00
parent 18227a6bc9
commit 3f8c65b06f
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 14 additions and 9 deletions
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23
fs/bpf_fs_kfuncs.c
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@ -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)