f2fs: don't use casefolded comparison for "." and ".."

Tryng to rename a directory that has all following properties fails with
EINVAL and triggers the 'WARN_ON_ONCE(!fscrypt_has_encryption_key(dir))'
in f2fs_match_ci_name():

    - The directory is casefolded
    - The directory is encrypted
    - The directory's encryption key is not yet set up
    - The parent directory is *not* encrypted

The problem is incorrect handling of the lookup of ".." to get the
parent reference to update.  fscrypt_setup_filename() treats ".." (and
".") specially, as it's never encrypted.  It's passed through as-is, and
setting up the directory's key is not attempted.  As the name isn't a
no-key name, f2fs treats it as a "normal" name and attempts a casefolded
comparison.  That breaks the assumption of the WARN_ON_ONCE() in
f2fs_match_ci_name() which assumes that for encrypted directories,
casefolded comparisons only happen when the directory's key is set up.

We could just remove this WARN_ON_ONCE().  However, since casefolding is
always a no-op on "." and ".." anyway, let's instead just not casefold
these names.  This results in the standard bytewise comparison.

Fixes: 7ad08a58bf67 ("f2fs: Handle casefolding with Encryption")
Cc: <stable@vger.kernel.org> # v5.11+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index a0e51937d92e..d5bd7932fb64 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -82,7 +82,8 @@ int f2fs_init_casefolded_name(const struct inode *dir,
 #if IS_ENABLED(CONFIG_UNICODE)
 	struct super_block *sb = dir->i_sb;
 
-	if (IS_CASEFOLDED(dir)) {
+	if (IS_CASEFOLDED(dir) &&
+	    !is_dot_dotdot(fname->usr_fname->name, fname->usr_fname->len)) {
 		fname->cf_name.name = f2fs_kmem_cache_alloc(f2fs_cf_name_slab,
 					GFP_NOFS, false, F2FS_SB(sb));
 		if (!fname->cf_name.name)