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authorEric Biggers <ebiggers@google.com>2020-11-17 23:56:05 -0800
committerEric Biggers <ebiggers@google.com>2020-11-24 15:10:27 -0800
commit159e1de201b6fca10bfec50405a3b53a561096a8 (patch)
treec2800ad873c8238a3017413f67e910a47f726875
parent3ceb6543e9cf6ed87cc1fbc6f23ca2db903564cd (diff)
downloadlinux-159e1de201b6fca10bfec50405a3b53a561096a8.tar.bz2
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>
-rw-r--r--fs/crypto/hooks.c5
-rw-r--r--include/linux/fscrypt.h34
2 files changed, 37 insertions, 2 deletions
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 20b0df47fe6a..061418be4b08 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -61,7 +61,7 @@ int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
return err;
/* ... in case we looked up no-key name before key was added */
- if (dentry->d_flags & DCACHE_NOKEY_NAME)
+ if (fscrypt_is_nokey_name(dentry))
return -ENOKEY;
if (!fscrypt_has_permitted_context(dir, inode))
@@ -86,7 +86,8 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
return err;
/* ... in case we looked up no-key name(s) before key was added */
- if ((old_dentry->d_flags | new_dentry->d_flags) & DCACHE_NOKEY_NAME)
+ if (fscrypt_is_nokey_name(old_dentry) ||
+ fscrypt_is_nokey_name(new_dentry))
return -ENOKEY;
if (old_dir != new_dir) {
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index a8f7a43f031b..8e1d31c959bf 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -111,6 +111,35 @@ static inline void fscrypt_handle_d_move(struct dentry *dentry)
dentry->d_flags &= ~DCACHE_NOKEY_NAME;
}
+/**
+ * fscrypt_is_nokey_name() - test whether a dentry is a no-key name
+ * @dentry: the dentry to check
+ *
+ * This returns true if the dentry is a no-key dentry. A no-key dentry is a
+ * dentry that was created in an encrypted directory that hasn't had its
+ * encryption key added yet. Such dentries may be either positive or negative.
+ *
+ * When a filesystem is asked to create a new filename in an encrypted directory
+ * and the new filename's dentry is a no-key dentry, it must fail the operation
+ * with ENOKEY. This includes ->create(), ->mkdir(), ->mknod(), ->symlink(),
+ * ->rename(), and ->link(). (However, ->rename() and ->link() are already
+ * handled by fscrypt_prepare_rename() and fscrypt_prepare_link().)
+ *
+ * This is necessary because creating a filename requires the directory's
+ * encryption key, but just checking for the key on the directory inode during
+ * the final filesystem operation doesn't guarantee that the key was available
+ * during the preceding dentry lookup. And the key must have already been
+ * available during the dentry lookup in order for it to have been checked
+ * whether the filename already exists in the directory and for the new file's
+ * dentry not to be invalidated due to it incorrectly having the no-key flag.
+ *
+ * Return: %true if the dentry is a no-key name
+ */
+static inline bool fscrypt_is_nokey_name(const struct dentry *dentry)
+{
+ return dentry->d_flags & DCACHE_NOKEY_NAME;
+}
+
/* crypto.c */
void fscrypt_enqueue_decrypt_work(struct work_struct *);
@@ -244,6 +273,11 @@ static inline void fscrypt_handle_d_move(struct dentry *dentry)
{
}
+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)
{