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Several parameters of the chacha20poly1305 functions require arrays of
an exact length. Use the new at_least keyword to instruct gcc and
clang to statically check that the caller is passing an object of at
least that length.
Here it is in action, with this faulty patch to wireguard's cookie.h:
struct cookie_checker {
u8 secret[NOISE_HASH_LEN];
- u8 cookie_encryption_key[NOISE_SYMMETRIC_KEY_LEN];
+ u8 cookie_encryption_key[NOISE_SYMMETRIC_KEY_LEN - 1];
u8 message_mac1_key[NOISE_SYMMETRIC_KEY_LEN];
If I try compiling this code, I get this helpful warning:
CC drivers/net/wireguard/cookie.o
drivers/net/wireguard/cookie.c: In function ‘wg_cookie_message_create’:
drivers/net/wireguard/cookie.c:193:9: warning: ‘xchacha20poly1305_encrypt’ reading 32 bytes from a region of size 31 [-Wstringop-overread]
193 | xchacha20poly1305_encrypt(dst->encrypted_cookie, cookie, COOKIE_LEN,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
194 | macs->mac1, COOKIE_LEN, dst->nonce,
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
195 | checker->cookie_encryption_key);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/wireguard/cookie.c:193:9: note: referencing argument 7 of type ‘const u8 *’ {aka ‘const unsigned char *’}
In file included from drivers/net/wireguard/messages.h:10,
from drivers/net/wireguard/cookie.h:9,
from drivers/net/wireguard/cookie.c:6:
include/crypto/chacha20poly1305.h:28:6: note: in a call to function ‘xchacha20poly1305_encrypt’
28 | void xchacha20poly1305_encrypt(u8 *dst, const u8 *src, const size_t src_len,
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: "Jason A. Donenfeld" <Jason@zx2c4.com>
Link: https://lore.kernel.org/r/20251123054819.2371989-4-Jason@zx2c4.com
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.