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b9f5ce27c8
Introduce the LANDLOCK_ACCESS_FS_TRUNCATE flag for file truncation. This flag hooks into the path_truncate, file_truncate and file_alloc_security LSM hooks and covers file truncation using truncate(2), ftruncate(2), open(2) with O_TRUNC, as well as creat(). This change also increments the Landlock ABI version, updates corresponding selftests, and updates code documentation to document the flag. In security/security.c, allocate security blobs at pointer-aligned offsets. This fixes the problem where one LSM's security blob can shift another LSM's security blob to an unaligned address (reported by Nathan Chancellor). The following operations are restricted: open(2): requires the LANDLOCK_ACCESS_FS_TRUNCATE right if a file gets implicitly truncated as part of the open() (e.g. using O_TRUNC). Notable special cases: * open(..., O_RDONLY|O_TRUNC) can truncate files as well in Linux * open() with O_TRUNC does *not* need the TRUNCATE right when it creates a new file. truncate(2) (on a path): requires the LANDLOCK_ACCESS_FS_TRUNCATE right. ftruncate(2) (on a file): requires that the file had the TRUNCATE right when it was previously opened. File descriptors acquired by other means than open(2) (e.g. memfd_create(2)) continue to support truncation with ftruncate(2). Cc: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Günther Noack <gnoack3000@gmail.com> Acked-by: Paul Moore <paul@paul-moore.com> (LSM) Link: https://lore.kernel.org/r/20221018182216.301684-5-gnoack3000@gmail.com Signed-off-by: Mickaël Salaün <mic@digikod.net>
96 lines
2.9 KiB
C
96 lines
2.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Landlock LSM - Filesystem management and hooks
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*
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* Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
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* Copyright © 2018-2020 ANSSI
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*/
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#ifndef _SECURITY_LANDLOCK_FS_H
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#define _SECURITY_LANDLOCK_FS_H
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/rcupdate.h>
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#include "ruleset.h"
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#include "setup.h"
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/**
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* struct landlock_inode_security - Inode security blob
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*
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* Enable to reference a &struct landlock_object tied to an inode (i.e.
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* underlying object).
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*/
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struct landlock_inode_security {
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/**
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* @object: Weak pointer to an allocated object. All assignments of a
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* new object are protected by the underlying inode->i_lock. However,
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* atomically disassociating @object from the inode is only protected
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* by @object->lock, from the time @object's usage refcount drops to
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* zero to the time this pointer is nulled out (cf. release_inode() and
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* hook_sb_delete()). Indeed, such disassociation doesn't require
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* inode->i_lock thanks to the careful rcu_access_pointer() check
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* performed by get_inode_object().
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*/
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struct landlock_object __rcu *object;
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};
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/**
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* struct landlock_file_security - File security blob
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*
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* This information is populated when opening a file in hook_file_open, and
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* tracks the relevant Landlock access rights that were available at the time
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* of opening the file. Other LSM hooks use these rights in order to authorize
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* operations on already opened files.
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*/
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struct landlock_file_security {
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/**
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* @allowed_access: Access rights that were available at the time of
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* opening the file. This is not necessarily the full set of access
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* rights available at that time, but it's the necessary subset as
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* needed to authorize later operations on the open file.
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*/
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access_mask_t allowed_access;
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};
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/**
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* struct landlock_superblock_security - Superblock security blob
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*
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* Enable hook_sb_delete() to wait for concurrent calls to release_inode().
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*/
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struct landlock_superblock_security {
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/**
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* @inode_refs: Number of pending inodes (from this superblock) that
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* are being released by release_inode().
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* Cf. struct super_block->s_fsnotify_inode_refs .
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*/
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atomic_long_t inode_refs;
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};
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static inline struct landlock_file_security *
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landlock_file(const struct file *const file)
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{
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return file->f_security + landlock_blob_sizes.lbs_file;
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}
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static inline struct landlock_inode_security *
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landlock_inode(const struct inode *const inode)
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{
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return inode->i_security + landlock_blob_sizes.lbs_inode;
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}
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static inline struct landlock_superblock_security *
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landlock_superblock(const struct super_block *const superblock)
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{
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return superblock->s_security + landlock_blob_sizes.lbs_superblock;
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}
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__init void landlock_add_fs_hooks(void);
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int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
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const struct path *const path,
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access_mask_t access_hierarchy);
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#endif /* _SECURITY_LANDLOCK_FS_H */
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