Re: [PATCH v2] ext4: fix memory leaks in ext4_fname_{setup_filename,prepare_lookup}

Eric Biggers [off-list ref] writes:

On Wed, Aug 02, 2023 at 10:49:31AM +0100, Luís Henriques wrote:

quoted

If casefolding the filename fails, we'll be leaking fscrypt_buf name.

fscrypt_buf => fscrypt_name

quoted

diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
index e20ac0654b3f..3c05c7f3415b 100644
--- a/fs/ext4/crypto.c
+++ b/fs/ext4/crypto.c

@@ -33,6 +33,8 @@ int ext4_fname_setup_filename(struct inode *dir, const struct qstr *iname,

struct fscrypt_name name;
int err;

err = fscrypt_setup_filename(dir, iname, lookup, &name);
if (err)
	return err;

ext4_fname_from_fscrypt_name(fname, &name);

 #if IS_ENABLED(CONFIG_UNICODE)
 	err = ext4_fname_setup_ci_filename(dir, iname, fname);
+	if (err)
+		fscrypt_free_filename(&name);
 #endif
 	return err;
 }

@@ -51,6 +53,8 @@ int ext4_fname_prepare_lookup(struct inode *dir, struct dentry *dentry,

struct fscrypt_name name;
int err;

err = fscrypt_prepare_lookup(dir, dentry, &name);
if (err)
	return err;

ext4_fname_from_fscrypt_name(fname, &name);

 #if IS_ENABLED(CONFIG_UNICODE)
 	err = ext4_fname_setup_ci_filename(dir, &dentry->d_name, fname);
+	if (err)
+		fscrypt_free_filename(&name);
 #endif
 	return err;
 }

This works, but it's a bit weird that the freeing happens on the original struct
fscrypt_name after it has already been "moved" to the struct ext4_filename by
ext4_fname_from_fscrypt_name().  That leaves a dangling pointer in the struct
ext4_filename.  Maybe you should call ext4_fname_free_filename() instead, even
though it would do some unnecessary work?

That makes sense, specially because fname is a parameter and it's probably
a good idea to clean-up everything before returning an error.  Thanks.

Cheers,
-- 
Luís