Files
kernel_google_redbull/include/linux/fscrypt_notsupp.h
Eric Biggers e675870b36 fscrypt: add fscrypt_symlink_getattr() for computing st_size
commit d18760560593e5af921f51a8c9b64b6109d634c2 upstream.

Add a helper function fscrypt_symlink_getattr() which will be called
from the various filesystems' ->getattr() methods to read and decrypt
the target of encrypted symlinks in order to report the correct st_size.

Detailed explanation:

As required by POSIX and as documented in various man pages, st_size for
a symlink is supposed to be the length of the symlink target.
Unfortunately, st_size has always been wrong for encrypted symlinks
because st_size is populated from i_size from disk, which intentionally
contains the length of the encrypted symlink target.  That's slightly
greater than the length of the decrypted symlink target (which is the
symlink target that userspace usually sees), and usually won't match the
length of the no-key encoded symlink target either.

This hadn't been fixed yet because reporting the correct st_size would
require reading the symlink target from disk and decrypting or encoding
it, which historically has been considered too heavyweight to do in
->getattr().  Also historically, the wrong st_size had only broken a
test (LTP lstat03) and there were no known complaints from real users.
(This is probably because the st_size of symlinks isn't used too often,
and when it is, typically it's for a hint for what buffer size to pass
to readlink() -- which a slightly-too-large size still works for.)

However, a couple things have changed now.  First, there have recently
been complaints about the current behavior from real users:

- Breakage in rpmbuild:
  https://github.com/rpm-software-management/rpm/issues/1682
  https://github.com/google/fscrypt/issues/305

- Breakage in toybox cpio:
  https://www.mail-archive.com/toybox@lists.landley.net/msg07193.html

- Breakage in libgit2: https://issuetracker.google.com/issues/189629152
  (on Android public issue tracker, requires login)

Second, we now cache decrypted symlink targets in ->i_link.  Therefore,
taking the performance hit of reading and decrypting the symlink target
in ->getattr() wouldn't be as big a deal as it used to be, since usually
it will just save having to do the same thing later.

Also note that eCryptfs ended up having to read and decrypt symlink
targets in ->getattr() as well, to fix this same issue; see
commit 3a60a1686f ("eCryptfs: Decrypt symlink target for stat size").

So, let's just bite the bullet, and read and decrypt the symlink target
in ->getattr() in order to report the correct st_size.  Add a function
fscrypt_symlink_getattr() which the filesystems will call to do this.

(Alternatively, we could store the decrypted size of symlinks on-disk.
But there isn't a great place to do so, and encryption is meant to hide
the original size to some extent; that property would be lost.)

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210702065350.209646-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-09-22 11:47:56 +02:00

244 lines
5.2 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
/*
* fscrypt_notsupp.h
*
* This stubs out the fscrypt functions for filesystems configured without
* encryption support.
*
* Do not include this file directly. Use fscrypt.h instead!
*/
#ifndef _LINUX_FSCRYPT_H
#error "Incorrect include of linux/fscrypt_notsupp.h!"
#endif
#ifndef _LINUX_FSCRYPT_NOTSUPP_H
#define _LINUX_FSCRYPT_NOTSUPP_H
static inline bool fscrypt_has_encryption_key(const struct inode *inode)
{
return false;
}
static inline bool fscrypt_dummy_context_enabled(struct inode *inode)
{
return false;
}
static inline bool fscrypt_is_nokey_name(const struct dentry *dentry)
{
return false;
}
/* crypto.c */
static inline void fscrypt_enqueue_decrypt_work(struct work_struct *work)
{
}
static inline struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *inode,
gfp_t gfp_flags)
{
return ERR_PTR(-EOPNOTSUPP);
}
static inline void fscrypt_release_ctx(struct fscrypt_ctx *ctx)
{
return;
}
static inline struct page *fscrypt_encrypt_page(const struct inode *inode,
struct page *page,
unsigned int len,
unsigned int offs,
u64 lblk_num, gfp_t gfp_flags)
{
return ERR_PTR(-EOPNOTSUPP);
}
static inline int fscrypt_decrypt_page(const struct inode *inode,
struct page *page,
unsigned int len, unsigned int offs,
u64 lblk_num)
{
return -EOPNOTSUPP;
}
static inline struct page *fscrypt_control_page(struct page *page)
{
WARN_ON_ONCE(1);
return ERR_PTR(-EINVAL);
}
static inline void fscrypt_restore_control_page(struct page *page)
{
return;
}
/* policy.c */
static inline int fscrypt_ioctl_set_policy(struct file *filp,
const void __user *arg)
{
return -EOPNOTSUPP;
}
static inline int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
{
return -EOPNOTSUPP;
}
static inline int fscrypt_has_permitted_context(struct inode *parent,
struct inode *child)
{
return 0;
}
static inline int fscrypt_inherit_context(struct inode *parent,
struct inode *child,
void *fs_data, bool preload)
{
return -EOPNOTSUPP;
}
/* keyinfo.c */
static inline int fscrypt_get_encryption_info(struct inode *inode)
{
return -EOPNOTSUPP;
}
static inline void fscrypt_put_encryption_info(struct inode *inode)
{
return;
}
/* fname.c */
static inline int fscrypt_setup_filename(struct inode *dir,
const struct qstr *iname,
int lookup, struct fscrypt_name *fname)
{
if (IS_ENCRYPTED(dir))
return -EOPNOTSUPP;
memset(fname, 0, sizeof(*fname));
fname->usr_fname = iname;
fname->disk_name.name = (unsigned char *)iname->name;
fname->disk_name.len = iname->len;
return 0;
}
static inline void fscrypt_free_filename(struct fscrypt_name *fname)
{
return;
}
static inline int fscrypt_fname_alloc_buffer(const struct inode *inode,
u32 max_encrypted_len,
struct fscrypt_str *crypto_str)
{
return -EOPNOTSUPP;
}
static inline void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
{
return;
}
static inline int fscrypt_fname_disk_to_usr(struct inode *inode,
u32 hash, u32 minor_hash,
const struct fscrypt_str *iname,
struct fscrypt_str *oname)
{
return -EOPNOTSUPP;
}
static inline bool fscrypt_match_name(const struct fscrypt_name *fname,
const u8 *de_name, u32 de_name_len)
{
/* Encryption support disabled; use standard comparison */
if (de_name_len != fname->disk_name.len)
return false;
return !memcmp(de_name, fname->disk_name.name, fname->disk_name.len);
}
/* bio.c */
static inline void fscrypt_decrypt_bio(struct bio *bio)
{
}
static inline void fscrypt_enqueue_decrypt_bio(struct fscrypt_ctx *ctx,
struct bio *bio)
{
}
static inline void fscrypt_pullback_bio_page(struct page **page, bool restore)
{
return;
}
static inline int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
sector_t pblk, unsigned int len)
{
return -EOPNOTSUPP;
}
/* hooks.c */
static inline int fscrypt_file_open(struct inode *inode, struct file *filp)
{
if (IS_ENCRYPTED(inode))
return -EOPNOTSUPP;
return 0;
}
static inline int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
struct dentry *dentry)
{
return -EOPNOTSUPP;
}
static inline int __fscrypt_prepare_rename(struct inode *old_dir,
struct dentry *old_dentry,
struct inode *new_dir,
struct dentry *new_dentry,
unsigned int flags)
{
return -EOPNOTSUPP;
}
static inline int __fscrypt_prepare_lookup(struct inode *dir,
struct dentry *dentry,
struct fscrypt_name *fname)
{
return -EOPNOTSUPP;
}
static inline int __fscrypt_prepare_symlink(struct inode *dir,
unsigned int len,
unsigned int max_len,
struct fscrypt_str *disk_link)
{
return -EOPNOTSUPP;
}
static inline int __fscrypt_encrypt_symlink(struct inode *inode,
const char *target,
unsigned int len,
struct fscrypt_str *disk_link)
{
return -EOPNOTSUPP;
}
static inline const char *fscrypt_get_symlink(struct inode *inode,
const void *caddr,
unsigned int max_size,
struct delayed_call *done)
{
return ERR_PTR(-EOPNOTSUPP);
}
static inline int fscrypt_symlink_getattr(const struct path *path,
struct kstat *stat)
{
return -EOPNOTSUPP;
}
#endif /* _LINUX_FSCRYPT_NOTSUPP_H */