From 35a33ff3807d3adb9daaf937f5bca002ffa9f84e Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 14 Apr 2022 01:50:38 +0200 Subject: [PATCH] random: use memmove instead of memcpy for remaining 32 bytes In order to immediately overwrite the old key on the stack, before servicing a userspace request for bytes, we use the remaining 32 bytes of block 0 as the key. This means moving indices 8,9,a,b,c,d,e,f -> 4,5,6,7,8,9,a,b. Since 4 < 8, for the kernel implementations of memcpy(), this doesn't actually appear to be a problem in practice. But relying on that characteristic seems a bit brittle. So let's change that to a proper memmove(), which is the by-the-books way of handling overlapping memory copies. Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 6b01b2b..3a293f9 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -333,7 +333,7 @@ static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE], chacha20_block(chacha_state, first_block); memcpy(key, first_block, CHACHA_KEY_SIZE); - memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len); + memmove(random_data, first_block + CHACHA_KEY_SIZE, random_data_len); memzero_explicit(first_block, sizeof(first_block)); } -- 2.7.4