[PATCH v2] ecryptfs: replace ecryptfs_from_hex() with hex2bin()

[DRIF ABDELMALEK MOHAMED SAID]

ecryptfs_from_hex() relied on the deprecated simple_strtoul(). Rather
than patching it to use kstrtoul(), its intended replacement, remove it
entirely and switch all call sites to the generic hex2bin() helper
from <linux/hex.h>, which already provides the same functionality.

Update call sites with the (u8 *) casts required by hex2bin()'s
signature.

All call sites guarantee that src is at least 2*dst_size bytes,
but nothing guarantees that src is valid hex, and also hex2bin's return
value needs to be checked, so we add a fail early check to call sites.

Signed-off-by: Drif Abdelmalek Mohamed Said
<drifabdelmalekmohamedsaid@xxxxxxxxx>
---
v2:
 - Added fail early check for hex2bin's return value
 - Fixed doubline empty lines
v1:https://lore.kernel.org/ecryptfs/20260829194528.5652-1-drifabdelmalekmohamedsaid@xxxxxxxxx/
 fs/ecryptfs/crypto.c          | 19 -------------------
 fs/ecryptfs/ecryptfs_kernel.h |  2 --
 fs/ecryptfs/keystore.c        | 20 +++++++++++++++++---
 3 files changed, 17 insertions(+), 24 deletions(-)

diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index e67119b6029c..059294df4b38 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -29,25 +29,6 @@
 #define DECRYPT                0
 #define ENCRYPT                1

-/**
- * ecryptfs_from_hex
- * @dst: Buffer to take the bytes from src hex; must be at least of
- *       size (src_size / 2)
- * @src: Buffer to be converted from a hex string representation to raw value
- * @dst_size: size of dst buffer, or number of hex characters pairs to convert
- */
-void ecryptfs_from_hex(char *dst, char *src, int dst_size)
-{
-       int x;
-       char tmp[3] = { 0, };
-
-       for (x = 0; x < dst_size; x++) {
-               tmp[0] = src[x * 2];
-               tmp[1] = src[x * 2 + 1];
-               dst[x] = (unsigned char)simple_strtol(tmp, NULL, 16);
-       }
-}
-
 static int ecryptfs_crypto_api_algify_cipher_name(char **algified_name,
                                                  const char *cipher_name,
                                                  const char *chaining_modifier)
diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index 58165928ed1e..0efda4cea71d 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -47,8 +47,6 @@ ecryptfs_to_hex(char *dst, char *src, size_t src_size)
        *end = '\0';
 }

-extern void ecryptfs_from_hex(char *dst, char *src, int dst_size);
-
 struct ecryptfs_key_record {
        unsigned char type;
        size_t enc_key_size;
diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index 51651314b7a6..4aaf62e61f3a 100644
--- a/fs/ecryptfs/keystore.c
+++ b/fs/ecryptfs/keystore.c
@@ -18,6 +18,7 @@
 #include <linux/random.h>
 #include <linux/scatterlist.h>
 #include <linux/slab.h>
+#include <linux/hex.h>
 #include "ecryptfs_kernel.h"

 /*
@@ -713,9 +714,14 @@ ecryptfs_write_tag_70_packet(char *dest, size_t
*remaining_bytes,
                goto out_free_unlock;
        }
        s->i += s->packet_size_len;
-       ecryptfs_from_hex(&dest[s->i],
+       rc = hex2bin((u8 *)&dest[s->i],
                          mount_crypt_stat->global_default_fnek_sig,
                          ECRYPTFS_SIG_SIZE);
+       if (rc) {
+               printk(KERN_ERR "%s: Invalid fnek sig [%s]; rc = [%d]\n",
+                          __func__,
mount_crypt_stat->global_default_fnek_sig, rc);
+               goto out_free_unlock;
+       }
        s->i += ECRYPTFS_SIG_SIZE;
        s->cipher_code = ecryptfs_code_for_cipher_string(
                mount_crypt_stat->global_default_fn_cipher_name,
@@ -2015,8 +2021,12 @@ write_tag_1_packet(char *dest, size_t *remaining_bytes,
        int rc = 0;

        (*packet_size) = 0;
-       ecryptfs_from_hex(key_rec->sig, auth_tok->token.private_key.signature,
+       rc = hex2bin((u8 *)key_rec->sig, auth_tok->token.private_key.signature,
                          ECRYPTFS_SIG_SIZE);
+       if (rc) {
+               printk(KERN_ERR "Invalid token private key signature;
rc = [%d]\n", rc);
+               goto out;
+       }
        encrypted_session_key_valid = 0;
        for (i = 0; i < crypt_stat->key_size; i++)
                encrypted_session_key_valid |=
@@ -2179,8 +2189,12 @@ write_tag_3_packet(char *dest, size_t *remaining_bytes,
        int rc = 0;

        (*packet_size) = 0;
-       ecryptfs_from_hex(key_rec->sig, auth_tok->token.password.signature,
+       rc = hex2bin((u8 *)key_rec->sig, auth_tok->token.password.signature,
                          ECRYPTFS_SIG_SIZE);
+       if (rc) {
+               printk(KERN_ERR "Invalid token password signature; rc
= [%d]\n", rc);
+               goto out;
+       }
        rc = ecryptfs_get_tfm_and_mutex_for_cipher_name(&tfm, &tfm_mutex,
                                                        crypt_stat->cipher);
        if (unlikely(rc)) {
--
2.43.0