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exportfs: add permission method

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This allows filesystems such as pidfs to provide their custom permission
checks.

Link: https://lore.kernel.org/r/20241129-work-pidfs-file_handle-v1-5-87d803a42495@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2024-11-29 14:38:04 +01:00
parent 6ebb05b48e
commit c220e216d6
No known key found for this signature in database
GPG key ID: 91C61BC06578DCA2
2 changed files with 30 additions and 22 deletions
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33
fs/fhandle.c
View file

@ -187,17 +187,6 @@ static int get_path_from_fd(int fd, struct path *root)
return 0;
}
enum handle_to_path_flags {
HANDLE_CHECK_PERMS = (1 << 0),
HANDLE_CHECK_SUBTREE = (1 << 1),
};
struct handle_to_path_ctx {
struct path root;
enum handle_to_path_flags flags;
unsigned int fh_flags;
};
static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
{
struct handle_to_path_ctx *ctx = context;
@ -279,13 +268,13 @@ static int do_handle_to_path(struct file_handle *handle, struct path *path,
return 0;
}
static inline bool may_decode_fh(struct handle_to_path_ctx *ctx,
static inline int may_decode_fh(struct handle_to_path_ctx *ctx,
unsigned int o_flags)
{
struct path *root = &ctx->root;
if (capable(CAP_DAC_READ_SEARCH))
return true;
return 0;
/*
* Allow relaxed permissions of file handles if the caller has
@ -309,7 +298,7 @@ static inline bool may_decode_fh(struct handle_to_path_ctx *ctx,
* There's only one dentry for each directory inode (VFS rule)...
*/
if (!(o_flags & O_DIRECTORY))
return false;
return -EPERM;
if (ns_capable(root->mnt->mnt_sb->s_user_ns, CAP_SYS_ADMIN))
ctx->flags = HANDLE_CHECK_PERMS;
@ -319,14 +308,14 @@ static inline bool may_decode_fh(struct handle_to_path_ctx *ctx,
!has_locked_children(real_mount(root->mnt), root->dentry))
ctx->flags = HANDLE_CHECK_PERMS | HANDLE_CHECK_SUBTREE;
else
return false;
return -EPERM;
/* Are we able to override DAC permissions? */
if (!ns_capable(current_user_ns(), CAP_DAC_READ_SEARCH))
return false;
return -EPERM;
ctx->fh_flags = EXPORT_FH_DIR_ONLY;
return true;
return 0;
}
static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
@ -336,15 +325,19 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
struct file_handle f_handle;
struct file_handle *handle = NULL;
struct handle_to_path_ctx ctx = {};
const struct export_operations *eops;
retval = get_path_from_fd(mountdirfd, &ctx.root);
if (retval)
goto out_err;
if (!may_decode_fh(&ctx, o_flags)) {
retval = -EPERM;
eops = ctx.root.mnt->mnt_sb->s_export_op;
if (eops && eops->permission)
retval = eops->permission(&ctx, o_flags);
else
retval = may_decode_fh(&ctx, o_flags);
if (retval)
goto out_path;
}
if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
retval = -EFAULT;

17
include/linux/exportfs.h
View file

@ -3,6 +3,7 @@
#define LINUX_EXPORTFS_H 1
#include <linux/types.h>
#include <linux/path.h>
struct dentry;
struct iattr;
@ -10,7 +11,6 @@ struct inode;
struct iomap;
struct super_block;
struct vfsmount;
struct path;
/* limit the handle size to NFSv4 handle size now */
#define MAX_HANDLE_SZ 128
@ -157,6 +157,17 @@ struct fid {
};
};
enum handle_to_path_flags {
HANDLE_CHECK_PERMS = (1 << 0),
HANDLE_CHECK_SUBTREE = (1 << 1),
};
struct handle_to_path_ctx {
struct path root;
enum handle_to_path_flags flags;
unsigned int fh_flags;
};
#define EXPORT_FH_CONNECTABLE 0x1 /* Encode file handle with parent */
#define EXPORT_FH_FID 0x2 /* File handle may be non-decodeable */
#define EXPORT_FH_DIR_ONLY 0x4 /* Only decode file handle for a directory */
@ -226,6 +237,9 @@ struct fid {
* is also a directory. In the event that it cannot be found, or storage
* space cannot be allocated, a %ERR_PTR should be returned.
*
* permission:
* Allow filesystems to specify a custom permission function.
*
* open:
* Allow filesystems to specify a custom open function.
*
@ -255,6 +269,7 @@ struct export_operations {
bool write, u32 *device_generation);
int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
int nr_iomaps, struct iattr *iattr);
int (*permission)(struct handle_to_path_ctx *ctx, unsigned int oflags);
struct file * (*open)(struct path *path, unsigned int oflags);
#define EXPORT_OP_NOWCC (0x1) /* don't collect v3 wcc data */
#define EXPORT_OP_NOSUBTREECHK (0x2) /* no subtree checking */