From cd0265fcd2eae9004c68ef2123a9dac0dc5a666a Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 18 Mar 2019 10:23:33 -0700 Subject: fscrypt: drop inode argument from fscrypt_get_ctx() The only reason the inode is being passed to fscrypt_get_ctx() is to verify that the encryption key is available. However, all callers already ensure this because if we get as far as trying to do I/O to an encrypted file without the key, there's already a bug. Therefore, remove this unnecessary argument. Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/fscrypt.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) (limited to 'include/linux') diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index e5194fc3983e..6cf8a34523ff 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -90,7 +90,7 @@ static inline bool fscrypt_dummy_context_enabled(struct inode *inode) /* crypto.c */ extern void fscrypt_enqueue_decrypt_work(struct work_struct *); -extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t); +extern struct fscrypt_ctx *fscrypt_get_ctx(gfp_t); extern void fscrypt_release_ctx(struct fscrypt_ctx *); extern struct page *fscrypt_encrypt_page(const struct inode *, struct page *, unsigned int, unsigned int, @@ -247,8 +247,7 @@ 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) +static inline struct fscrypt_ctx *fscrypt_get_ctx(gfp_t gfp_flags) { return ERR_PTR(-EOPNOTSUPP); } -- cgit v1.2.3 From e37a784d8b6a1e726de5ddc7b4809c086a08db09 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Thu, 11 Apr 2019 14:32:15 -0700 Subject: fscrypt: use READ_ONCE() to access ->i_crypt_info ->i_crypt_info starts out NULL and may later be locklessly set to a non-NULL value by the cmpxchg() in fscrypt_get_encryption_info(). But ->i_crypt_info is used directly, which technically is incorrect. It's a data race, and it doesn't include the data dependency barrier needed to safely dereference the pointer on at least one architecture. Fix this by using READ_ONCE() instead. Note: we don't need to use smp_load_acquire(), since dereferencing the pointer only requires a data dependency barrier, which is already included in READ_ONCE(). We also don't need READ_ONCE() in places where ->i_crypt_info is unconditionally dereferenced, since it must have already been checked. Also downgrade the cmpxchg() to cmpxchg_release(), since RELEASE semantics are sufficient on the write side. Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/fscrypt.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index 6cf8a34523ff..ec8ab7108599 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -79,7 +79,8 @@ struct fscrypt_ctx { static inline bool fscrypt_has_encryption_key(const struct inode *inode) { - return (inode->i_crypt_info != NULL); + /* pairs with cmpxchg_release() in fscrypt_get_encryption_info() */ + return READ_ONCE(inode->i_crypt_info) != NULL; } static inline bool fscrypt_dummy_context_enabled(struct inode *inode) -- cgit v1.2.3 From 6cc248684d3d23bbd073ae2fa73d3416c0558909 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 20 Mar 2019 11:39:09 -0700 Subject: fscrypt: clean up and improve dentry revalidation Make various improvements to fscrypt dentry revalidation: - Don't try to handle the case where the per-directory key is removed, as this can't happen without the inode (and dentries) being evicted. - Flag ciphertext dentries rather than plaintext dentries, since it's ciphertext dentries that need the special handling. - Avoid doing unnecessary work for non-ciphertext dentries. - When revalidating ciphertext dentries, try to set up the directory's i_crypt_info to make sure the key is really still absent, rather than invalidating all negative dentries as the previous code did. An old comment suggested we can't do this for locking reasons, but AFAICT this comment was outdated and it actually works fine. Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/dcache.h | 2 +- include/linux/fscrypt.h | 6 ++---- 2 files changed, 3 insertions(+), 5 deletions(-) (limited to 'include/linux') diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 60996e64c579..9b3b75d3bd21 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -212,7 +212,7 @@ struct dentry_operations { #define DCACHE_MAY_FREE 0x00800000 #define DCACHE_FALLTHRU 0x01000000 /* Fall through to lower layer */ -#define DCACHE_ENCRYPTED_WITH_KEY 0x02000000 /* dir is encrypted with a valid key */ +#define DCACHE_ENCRYPTED_NAME 0x02000000 /* Encrypted name (dir key was unavailable) */ #define DCACHE_OP_REAL 0x04000000 #define DCACHE_PAR_LOOKUP 0x10000000 /* being looked up (with parent locked shared) */ diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index ec8ab7108599..09e368a515d1 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -545,10 +545,8 @@ static inline int fscrypt_prepare_rename(struct inode *old_dir, * filenames are presented in encrypted form. Therefore, we'll try to set up * the directory's encryption key, but even without it the lookup can continue. * - * To allow invalidating stale dentries if the directory's encryption key is - * added later, we also install a custom ->d_revalidate() method and use the - * DCACHE_ENCRYPTED_WITH_KEY flag to indicate whether a given dentry is a - * plaintext name (flag set) or a ciphertext name (flag cleared). + * This also installs a custom ->d_revalidate() method which will invalidate the + * dentry if it was created without the key and the key is later added. * * Return: 0 on success, -errno if a problem occurred while setting up the * encryption key -- cgit v1.2.3 From 968dd6d0c6d6b6a989c6ddb9e2584a031b83e7b5 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 20 Mar 2019 11:39:10 -0700 Subject: fscrypt: fix race allowing rename() and link() of ciphertext dentries Close some race conditions where fscrypt allowed rename() and link() on ciphertext dentries that had been looked up just prior to the key being concurrently added. It's better to return -ENOKEY in this case. This avoids doing the nonsensical thing of encrypting the names a second time when searching for the actual on-disk dir entries. It also guarantees that DCACHE_ENCRYPTED_NAME dentries are never rename()d, so the dcache won't have support all possible combinations of moving DCACHE_ENCRYPTED_NAME around during __d_move(). Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/fscrypt.h | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index 09e368a515d1..855f743c226e 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -215,7 +215,8 @@ extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t, /* hooks.c */ extern int fscrypt_file_open(struct inode *inode, struct file *filp); -extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir); +extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, + struct dentry *dentry); extern int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, @@ -401,8 +402,8 @@ static inline int fscrypt_file_open(struct inode *inode, struct file *filp) return 0; } -static inline int __fscrypt_prepare_link(struct inode *inode, - struct inode *dir) +static inline int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, + struct dentry *dentry) { return -EOPNOTSUPP; } @@ -497,7 +498,7 @@ static inline int fscrypt_prepare_link(struct dentry *old_dentry, struct dentry *dentry) { if (IS_ENCRYPTED(dir)) - return __fscrypt_prepare_link(d_inode(old_dentry), dir); + return __fscrypt_prepare_link(d_inode(old_dentry), dir, dentry); return 0; } -- cgit v1.2.3 From 0bf3d5c1604ecbbd4e49e9f5b3c79152b87adb0d Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 20 Mar 2019 11:39:11 -0700 Subject: fs, fscrypt: clear DCACHE_ENCRYPTED_NAME when unaliasing directory Make __d_move() clear DCACHE_ENCRYPTED_NAME on the source dentry. This is needed for when d_splice_alias() moves a directory's encrypted alias to its decrypted alias as a result of the encryption key being added. Otherwise, the decrypted alias will incorrectly be invalidated on the next lookup, causing problems such as unmounting a mount the user just mount()ed there. Note that we don't have to support arbitrary moves of this flag because fscrypt doesn't allow dentries with DCACHE_ENCRYPTED_NAME to be the source or target of a rename(). Fixes: 28b4c263961c ("ext4 crypto: revalidate dentry after adding or removing the key") Reported-by: Sarthak Kukreti Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/fscrypt.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'include/linux') diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index 855f743c226e..76c518f1e4c7 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -89,6 +89,18 @@ static inline bool fscrypt_dummy_context_enabled(struct inode *inode) inode->i_sb->s_cop->dummy_context(inode); } +/* + * When d_splice_alias() moves a directory's encrypted alias to its decrypted + * alias as a result of the encryption key being added, DCACHE_ENCRYPTED_NAME + * must be cleared. Note that we don't have to support arbitrary moves of this + * flag because fscrypt doesn't allow encrypted aliases to be the source or + * target of a rename(). + */ +static inline void fscrypt_handle_d_move(struct dentry *dentry) +{ + dentry->d_flags &= ~DCACHE_ENCRYPTED_NAME; +} + /* crypto.c */ extern void fscrypt_enqueue_decrypt_work(struct work_struct *); extern struct fscrypt_ctx *fscrypt_get_ctx(gfp_t); @@ -244,6 +256,10 @@ static inline bool fscrypt_dummy_context_enabled(struct inode *inode) return false; } +static inline void fscrypt_handle_d_move(struct dentry *dentry) +{ +} + /* crypto.c */ static inline void fscrypt_enqueue_decrypt_work(struct work_struct *work) { -- cgit v1.2.3 From b01531db6cec2aa330dbc91bfbfaaef4a0d387a4 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 20 Mar 2019 11:39:13 -0700 Subject: fscrypt: fix race where ->lookup() marks plaintext dentry as ciphertext ->lookup() in an encrypted directory begins as follows: 1. fscrypt_prepare_lookup(): a. Try to load the directory's encryption key. b. If the key is unavailable, mark the dentry as a ciphertext name via d_flags. 2. fscrypt_setup_filename(): a. Try to load the directory's encryption key. b. If the key is available, encrypt the name (treated as a plaintext name) to get the on-disk name. Otherwise decode the name (treated as a ciphertext name) to get the on-disk name. But if the key is concurrently added, it may be found at (2a) but not at (1a). In this case, the dentry will be wrongly marked as a ciphertext name even though it was actually treated as plaintext. This will cause the dentry to be wrongly invalidated on the next lookup, potentially causing problems. For example, if the racy ->lookup() was part of sys_mount(), then the new mount will be detached when anything tries to access it. This is despite the mountpoint having a plaintext path, which should remain valid now that the key was added. Of course, this is only possible if there's a userspace race. Still, the additional kernel-side race is confusing and unexpected. Close the kernel-side race by changing fscrypt_prepare_lookup() to also set the on-disk filename (step 2b), consistent with the d_flags update. Fixes: 28b4c263961c ("ext4 crypto: revalidate dentry after adding or removing the key") Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/fscrypt.h | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) (limited to 'include/linux') diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index 76c518f1e4c7..abe7081b6b22 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -33,6 +33,7 @@ struct fscrypt_name { u32 hash; u32 minor_hash; struct fscrypt_str crypto_buf; + bool is_ciphertext_name; }; #define FSTR_INIT(n, l) { .name = n, .len = l } @@ -234,7 +235,8 @@ extern int __fscrypt_prepare_rename(struct inode *old_dir, struct inode *new_dir, struct dentry *new_dentry, unsigned int flags); -extern int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry); +extern int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry, + struct fscrypt_name *fname); extern int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, unsigned int max_len, struct fscrypt_str *disk_link); @@ -347,7 +349,7 @@ static inline int fscrypt_setup_filename(struct inode *dir, if (IS_ENCRYPTED(dir)) return -EOPNOTSUPP; - memset(fname, 0, sizeof(struct fscrypt_name)); + memset(fname, 0, sizeof(*fname)); fname->usr_fname = iname; fname->disk_name.name = (unsigned char *)iname->name; fname->disk_name.len = iname->len; @@ -434,7 +436,8 @@ static inline int __fscrypt_prepare_rename(struct inode *old_dir, } static inline int __fscrypt_prepare_lookup(struct inode *dir, - struct dentry *dentry) + struct dentry *dentry, + struct fscrypt_name *fname) { return -EOPNOTSUPP; } @@ -555,25 +558,32 @@ static inline int fscrypt_prepare_rename(struct inode *old_dir, * fscrypt_prepare_lookup - prepare to lookup a name in a possibly-encrypted directory * @dir: directory being searched * @dentry: filename being looked up - * @flags: lookup flags + * @fname: (output) the name to use to search the on-disk directory * - * Prepare for ->lookup() in a directory which may be encrypted. Lookups can be - * done with or without the directory's encryption key; without the key, + * Prepare for ->lookup() in a directory which may be encrypted by determining + * the name that will actually be used to search the directory on-disk. Lookups + * can be done with or without the directory's encryption key; without the key, * filenames are presented in encrypted form. Therefore, we'll try to set up * the directory's encryption key, but even without it the lookup can continue. * * This also installs a custom ->d_revalidate() method which will invalidate the * dentry if it was created without the key and the key is later added. * - * Return: 0 on success, -errno if a problem occurred while setting up the - * encryption key + * Return: 0 on success; -ENOENT if key is unavailable but the filename isn't a + * correctly formed encoded ciphertext name, so a negative dentry should be + * created; or another -errno code. */ static inline int fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry, - unsigned int flags) + struct fscrypt_name *fname) { if (IS_ENCRYPTED(dir)) - return __fscrypt_prepare_lookup(dir, dentry); + return __fscrypt_prepare_lookup(dir, dentry, fname); + + memset(fname, 0, sizeof(*fname)); + fname->usr_fname = &dentry->d_name; + fname->disk_name.name = (unsigned char *)dentry->d_name.name; + fname->disk_name.len = dentry->d_name.len; return 0; } -- cgit v1.2.3 From 2c58d548f5706d085c4b009f6abb945220460632 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 10 Apr 2019 13:21:15 -0700 Subject: fscrypt: cache decrypted symlink target in ->i_link Path lookups that traverse encrypted symlink(s) are very slow because each encrypted symlink needs to be decrypted each time it's followed. This also involves dropping out of rcu-walk mode. Make encrypted symlinks faster by caching the decrypted symlink target in ->i_link. The first call to fscrypt_get_symlink() sets it. Then, the existing VFS path lookup code uses the non-NULL ->i_link to take the fast path where ->get_link() isn't called, and lookups in rcu-walk mode remain in rcu-walk mode. Also set ->i_link immediately when a new encrypted symlink is created. To safely free the symlink target after an RCU grace period has elapsed, introduce a new function fscrypt_free_inode(), and make the relevant filesystems call it just before actually freeing the inode. Cc: Al Viro Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/fscrypt.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/linux') diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index abe7081b6b22..28c74e0a7231 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -128,6 +128,7 @@ extern int fscrypt_inherit_context(struct inode *, struct inode *, /* keyinfo.c */ extern int fscrypt_get_encryption_info(struct inode *); extern void fscrypt_put_encryption_info(struct inode *); +extern void fscrypt_free_inode(struct inode *); /* fname.c */ extern int fscrypt_setup_filename(struct inode *, const struct qstr *, @@ -341,6 +342,10 @@ static inline void fscrypt_put_encryption_info(struct inode *inode) return; } +static inline void fscrypt_free_inode(struct inode *inode) +{ +} + /* fname.c */ static inline int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname, -- cgit v1.2.3