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authorEric Biggers <ebiggers@google.com>2020-11-18 10:56:05 +0300
committerEric Biggers <ebiggers@google.com>2020-11-25 02:10:27 +0300
commit159e1de201b6fca10bfec50405a3b53a561096a8 (patch)
treec2800ad873c8238a3017413f67e910a47f726875 /fs/crypto
parent3ceb6543e9cf6ed87cc1fbc6f23ca2db903564cd (diff)
downloadlinux-159e1de201b6fca10bfec50405a3b53a561096a8.tar.xz
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>
Diffstat (limited to 'fs/crypto')
-rw-r--r--fs/crypto/hooks.c5
1 files changed, 3 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) {