mirror of https://gitee.com/openkylin/linux.git
fscrypt: add fscrypt_is_nokey_name()
It's possible to create a duplicate filename in an encrypted directory by creating a file concurrently with adding the encryption key. Specifically, sys_open(O_CREAT) (or sys_mkdir(), sys_mknod(), or sys_symlink()) can lookup the target filename while the directory's encryption key hasn't been added yet, resulting in a negative no-key dentry. The VFS then calls ->create() (or ->mkdir(), ->mknod(), or ->symlink()) because the dentry is negative. Normally, ->create() would return -ENOKEY due to the directory's key being unavailable. However, if the key was added between the dentry lookup and ->create(), then the filesystem will go ahead and try to create the file. If the target filename happens to already exist as a normal name (not a no-key name), a duplicate filename may be added to the directory. In order to fix this, we need to fix the filesystems to prevent ->create(), ->mkdir(), ->mknod(), and ->symlink() on no-key names. (->rename() and ->link() need it too, but those are already handled correctly by fscrypt_prepare_rename() and fscrypt_prepare_link().) In preparation for this, add a helper function fscrypt_is_nokey_name() that filesystems can use to do this check. Use this helper function for the existing checks that fs/crypto/ does for rename and link. Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20201118075609.120337-2-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
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@ -61,7 +61,7 @@ int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
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return err;
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/* ... in case we looked up no-key name before key was added */
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if (dentry->d_flags & DCACHE_NOKEY_NAME)
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if (fscrypt_is_nokey_name(dentry))
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return -ENOKEY;
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if (!fscrypt_has_permitted_context(dir, inode))
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@ -86,7 +86,8 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
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return err;
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/* ... in case we looked up no-key name(s) before key was added */
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if ((old_dentry->d_flags | new_dentry->d_flags) & DCACHE_NOKEY_NAME)
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if (fscrypt_is_nokey_name(old_dentry) ||
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fscrypt_is_nokey_name(new_dentry))
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return -ENOKEY;
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if (old_dir != new_dir) {
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@ -111,6 +111,35 @@ static inline void fscrypt_handle_d_move(struct dentry *dentry)
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dentry->d_flags &= ~DCACHE_NOKEY_NAME;
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}
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/**
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* fscrypt_is_nokey_name() - test whether a dentry is a no-key name
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* @dentry: the dentry to check
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*
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* This returns true if the dentry is a no-key dentry. A no-key dentry is a
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* dentry that was created in an encrypted directory that hasn't had its
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* encryption key added yet. Such dentries may be either positive or negative.
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*
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* When a filesystem is asked to create a new filename in an encrypted directory
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* and the new filename's dentry is a no-key dentry, it must fail the operation
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* with ENOKEY. This includes ->create(), ->mkdir(), ->mknod(), ->symlink(),
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* ->rename(), and ->link(). (However, ->rename() and ->link() are already
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* handled by fscrypt_prepare_rename() and fscrypt_prepare_link().)
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*
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* This is necessary because creating a filename requires the directory's
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* encryption key, but just checking for the key on the directory inode during
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* the final filesystem operation doesn't guarantee that the key was available
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* during the preceding dentry lookup. And the key must have already been
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* available during the dentry lookup in order for it to have been checked
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* whether the filename already exists in the directory and for the new file's
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* dentry not to be invalidated due to it incorrectly having the no-key flag.
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*
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* Return: %true if the dentry is a no-key name
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*/
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static inline bool fscrypt_is_nokey_name(const struct dentry *dentry)
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{
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return dentry->d_flags & DCACHE_NOKEY_NAME;
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}
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/* crypto.c */
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void fscrypt_enqueue_decrypt_work(struct work_struct *);
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@ -244,6 +273,11 @@ static inline void fscrypt_handle_d_move(struct dentry *dentry)
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{
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}
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static inline bool fscrypt_is_nokey_name(const struct dentry *dentry)
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{
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return false;
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}
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/* crypto.c */
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static inline void fscrypt_enqueue_decrypt_work(struct work_struct *work)
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{
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