On Wed, Oct 01, 2025 at 09:07:07AM -0700, Breno Leitao wrote:

Loading a large (~2.1G) files with kexec crashes the host with when running:

# kexec --load kernel --initrd initrd_with_2G_or_more

UBSAN: signed-integer-overflow in ./include/crypto/sha256_base.h:64:19 34152083 * 64 cannot be represented in type 'int' ... BUG: unable to handle page fault for address: ff9fffff83b624c0 sha256_update (lib/crypto/sha256.c:137) crypto_sha256_update (crypto/sha256_generic.c:40) kexec_calculate_store_digests (kernel/kexec_file.c:769) __se_sys_kexec_file_load (kernel/kexec_file.c:397 kernel/kexec_file.c:332) ...

(Line numbers based on commit da274362a7bd9 ("Linux 6.12.49")

This is not happening upstream (v6.16+), given that `block` type was upgraded from "int" to "size_t" in commit 74a43a2cf5e8 ("crypto: lib/sha256 - Move partial block handling out")

Upgrade the block type similar to the commit above, avoiding hitting the overflow.

This patch is only suitable for the stable tree, and before 6.16, which got commit 74a43a2cf5e8 ("crypto: lib/sha256 - Move partial block handling out")

Signed-off-by: Breno Leitao leitao@debian.org Fixes: 11b8d5ef9138 ("crypto: sha256 - implement base layer for SHA-256") # not after v6.16 Reported-by: Michael van der Westhuizen rmikey@meta.com Reported-by: Tobias Fleig tfleig@meta.com

---

include/crypto/sha256_base.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/crypto/sha256_base.h b/include/crypto/sha256_base.h index e0418818d63c8..fa63af10102b2 100644 --- a/include/crypto/sha256_base.h +++ b/include/crypto/sha256_base.h @@ -44,7 +44,7 @@ static inline int lib_sha256_base_do_update(struct sha256_state *sctx, sctx->count += len; if (unlikely((partial + len) >= SHA256_BLOCK_SIZE)) {

• int blocks;
  

• size_t blocks;
  

if (partial) { int p = SHA256_BLOCK_SIZE - partial;

---

This looks fine, but technically 'unsigned int' would be more appropriate here, given the context. If we look at the whole function in 6.12, we can see that it took an 'unsigned int' length:

static inline int lib_sha256_base_do_update(struct sha256_state *sctx, const u8 *data, unsigned int len, sha256_block_fn *block_fn) { unsigned int partial = sctx->count % SHA256_BLOCK_SIZE;

sctx->count += len;

if (unlikely((partial + len) >= SHA256_BLOCK_SIZE)) { - int blocks; + size_t blocks;

if (partial) { int p = SHA256_BLOCK_SIZE - partial;

memcpy(sctx->buf + partial, data, p); data += p; len -= p;

block_fn(sctx, sctx->buf, 1); }

blocks = len / SHA256_BLOCK_SIZE; len %= SHA256_BLOCK_SIZE;

if (blocks) { block_fn(sctx, data, blocks); data += blocks * SHA256_BLOCK_SIZE; } partial = 0; } if (len) memcpy(sctx->buf + partial, data, len);

return 0; }

This also suggests that files with lengths greater than UINT_MAX are still broken. Is that okay?

Anyway, I'm glad that I fixed all these functions to use size_t lengths in newer kernels...

- Eric