random: cleanup UUID handling

Rather than hard coding various lengths, we can use the right constants.
Strings should be `char *` while buffers should be `u8 *`. Rather than
have a nonsensical and unused maxlength, just remove it. Finally, use
snprintf instead of sprintf, just out of good hygiene.

As well, remove the old comment about returning a binary UUID via the
binary sysctl syscall. That syscall was removed from the kernel in 5.5,
and actually, the "uuid_strategy" function and related infrastructure
for even serving it via the binary sysctl syscall was removed with
894d2491153a ("sysctl drivers: Remove dead binary sysctl support") back
in 2.6.33.

Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 536237a..4cdf395 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1661,22 +1661,25 @@ const struct file_operations urandom_fops = {
 static int sysctl_random_min_urandom_seed = 60;
 static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS;
 static int sysctl_poolsize = POOL_BITS;
-static char sysctl_bootid[16];
+static u8 sysctl_bootid[UUID_SIZE];
 
 /*
  * This function is used to return both the bootid UUID, and random
- * UUID.  The difference is in whether table->data is NULL; if it is,
+ * UUID. The difference is in whether table->data is NULL; if it is,
  * then a new UUID is generated and returned to the user.
- *
- * If the user accesses this via the proc interface, the UUID will be
- * returned as an ASCII string in the standard UUID format; if via the
- * sysctl system call, as 16 bytes of binary data.
  */
 static int proc_do_uuid(struct ctl_table *table, int write, void *buffer,
                        size_t *lenp, loff_t *ppos)
 {
-       struct ctl_table fake_table;
-       unsigned char buf[64], tmp_uuid[16], *uuid;
+       u8 tmp_uuid[UUID_SIZE], *uuid;
+       char uuid_string[UUID_STRING_LEN + 1];
+       struct ctl_table fake_table = {
+               .data = uuid_string,
+               .maxlen = UUID_STRING_LEN
+       };
+
+       if (write)
+               return -EPERM;
 
        uuid = table->data;
        if (!uuid) {
@@ -1691,12 +1694,8 @@ static int proc_do_uuid(struct ctl_table *table, int write, void *buffer,
                spin_unlock(&bootid_spinlock);
        }
 
-       sprintf(buf, "%pU", uuid);
-
-       fake_table.data = buf;
-       fake_table.maxlen = sizeof(buf);
-
-       return proc_dostring(&fake_table, write, buffer, lenp, ppos);
+       snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
+       return proc_dostring(&fake_table, 0, buffer, lenp, ppos);
 }
 
 static struct ctl_table random_table[] = {
@@ -1731,13 +1730,11 @@ static struct ctl_table random_table[] = {
        {
                .procname       = "boot_id",
                .data           = &sysctl_bootid,
-               .maxlen         = 16,
                .mode           = 0444,
                .proc_handler   = proc_do_uuid,
        },
        {
                .procname       = "uuid",
-               .maxlen         = 16,
                .mode           = 0444,
                .proc_handler   = proc_do_uuid,
        },