Re: [PATCH][next] crypto/nx: Avoid potential -Wflex-array-member-not-at-end warning
From: Kees Cook
Date: Mon Apr 29 2024 - 13:05:36 EST
On Mon, Mar 25, 2024 at 03:01:56PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
> ready to enable it globally.
>
> Use the `__struct_group()` helper to separate the flexible array
> from the rest of the members in flexible `struct nx842_crypto_header`,
> through tagged `struct nx842_crypto_header_hdr`, and avoid embedding
> the flexible-array member in the middle of `struct nx842_crypto_ctx`.
>
> Also, use `container_of()` whenever we need to retrieve a pointer to
> the flexible structure.
>
> This code was detected with the help of Coccinelle, and audited and
> modified manually.
>
> Link: https://github.com/KSPP/linux/issues/202
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> ---
> drivers/crypto/nx/nx-842.c | 6 ++++--
> drivers/crypto/nx/nx-842.h | 11 +++++++----
> 2 files changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/crypto/nx/nx-842.c b/drivers/crypto/nx/nx-842.c
> index 2ab90ec10e61..82214cde2bcd 100644
> --- a/drivers/crypto/nx/nx-842.c
> +++ b/drivers/crypto/nx/nx-842.c
> @@ -251,7 +251,9 @@ int nx842_crypto_compress(struct crypto_tfm *tfm,
> u8 *dst, unsigned int *dlen)
> {
> struct nx842_crypto_ctx *ctx = crypto_tfm_ctx(tfm);
> - struct nx842_crypto_header *hdr = &ctx->header;
> + struct nx842_crypto_header *hdr =
> + container_of(&ctx->header,
> + struct nx842_crypto_header, hdr);
> struct nx842_crypto_param p;
> struct nx842_constraints c = *ctx->driver->constraints;
> unsigned int groups, hdrsize, h;
> @@ -490,7 +492,7 @@ int nx842_crypto_decompress(struct crypto_tfm *tfm,
> }
>
> memcpy(&ctx->header, src, hdr_len);
> - hdr = &ctx->header;
> + hdr = container_of(&ctx->header, struct nx842_crypto_header, hdr);
>
> for (n = 0; n < hdr->groups; n++) {
> /* ignore applies to last group */
> diff --git a/drivers/crypto/nx/nx-842.h b/drivers/crypto/nx/nx-842.h
> index 7590bfb24d79..1f42c83d2683 100644
> --- a/drivers/crypto/nx/nx-842.h
> +++ b/drivers/crypto/nx/nx-842.h
> @@ -157,9 +157,12 @@ struct nx842_crypto_header_group {
> } __packed;
>
> struct nx842_crypto_header {
> - __be16 magic; /* NX842_CRYPTO_MAGIC */
> - __be16 ignore; /* decompressed end bytes to ignore */
> - u8 groups; /* total groups in this header */
> + /* New members must be added within the __struct_group() macro below. */
> + __struct_group(nx842_crypto_header_hdr, hdr, __packed,
> + __be16 magic; /* NX842_CRYPTO_MAGIC */
> + __be16 ignore; /* decompressed end bytes to ignore */
> + u8 groups; /* total groups in this header */
> + );
> struct nx842_crypto_header_group group[];
> } __packed;
>
> @@ -171,7 +174,7 @@ struct nx842_crypto_ctx {
> u8 *wmem;
> u8 *sbounce, *dbounce;
>
> - struct nx842_crypto_header header;
> + struct nx842_crypto_header_hdr header;
> struct nx842_crypto_header_group group[NX842_CRYPTO_GROUP_MAX];
>
> struct nx842_driver *driver;
Hmm. I think commit 03952d980153 ("crypto: nx - make platform drivers
directly register with crypto") incorrectly added "struct nx842_driver
*driver" to the end of struct nx842_crypto_ctx. I think it should be
before "header".
Then I see:
#define NX842_CRYPTO_HEADER_SIZE(g) \
(sizeof(struct nx842_crypto_header) + \
sizeof(struct nx842_crypto_header_group) * (g))
This is just struct_size(), really. And nothing uses:
#define NX842_CRYPTO_HEADER_MAX_SIZE \
NX842_CRYPTO_HEADER_SIZE(NX842_CRYPTO_GROUP_MAX)
And then looking for what uses struct nx842_crypto_ctx's "group" member,
I don't see anything except some sizeof()s:
drivers/crypto/nx/nx-common-powernv.c:1044: .cra_ctxsize = sizeof(struct nx842_crypto_ctx),
drivers/crypto/nx/nx-common-pseries.c:1021: .cra_ctxsize = sizeof(struct nx842_crypto_ctx),
This is just a maximally sized ctx (as if the group count were
NX842_CRYPTO_GROUP_MAX), which we could use struct_size for again:
.cra_ctxsize = struct_size_t(struct nx842_crypto_ctx, header.group,
NX842_CRYPTO_GROUP_MAX),
So then "group" can be entirely removed from struct nx842_crypto_ctx.
The result means we can also add __counted_by:
diff --git a/drivers/crypto/nx/nx-842.c b/drivers/crypto/nx/nx-842.c
index 2ab90ec10e61..144972fe2e6f 100644
--- a/drivers/crypto/nx/nx-842.c
+++ b/drivers/crypto/nx/nx-842.c
@@ -62,10 +62,7 @@
*/
#define NX842_CRYPTO_MAGIC (0xf842)
#define NX842_CRYPTO_HEADER_SIZE(g) \
- (sizeof(struct nx842_crypto_header) + \
- sizeof(struct nx842_crypto_header_group) * (g))
-#define NX842_CRYPTO_HEADER_MAX_SIZE \
- NX842_CRYPTO_HEADER_SIZE(NX842_CRYPTO_GROUP_MAX)
+ struct_size_t(nx842_crypto_header, group, g)
/* bounce buffer size */
#define BOUNCE_BUFFER_ORDER (2)
diff --git a/drivers/crypto/nx/nx-842.h b/drivers/crypto/nx/nx-842.h
index 7590bfb24d79..70d9f99a4595 100644
--- a/drivers/crypto/nx/nx-842.h
+++ b/drivers/crypto/nx/nx-842.h
@@ -160,7 +160,7 @@ struct nx842_crypto_header {
__be16 magic; /* NX842_CRYPTO_MAGIC */
__be16 ignore; /* decompressed end bytes to ignore */
u8 groups; /* total groups in this header */
- struct nx842_crypto_header_group group[];
+ struct nx842_crypto_header_group group[] __counted_by(groups);
} __packed;
#define NX842_CRYPTO_GROUP_MAX (0x20)
@@ -171,10 +171,9 @@ struct nx842_crypto_ctx {
u8 *wmem;
u8 *sbounce, *dbounce;
- struct nx842_crypto_header header;
- struct nx842_crypto_header_group group[NX842_CRYPTO_GROUP_MAX];
-
struct nx842_driver *driver;
+
+ struct nx842_crypto_header header;
};
int nx842_crypto_init(struct crypto_tfm *tfm, struct nx842_driver *driver);
diff --git a/drivers/crypto/nx/nx-common-powernv.c b/drivers/crypto/nx/nx-common-powernv.c
index 8c859872c183..22ab4a5885f2 100644
--- a/drivers/crypto/nx/nx-common-powernv.c
+++ b/drivers/crypto/nx/nx-common-powernv.c
@@ -1041,7 +1041,8 @@ static struct crypto_alg nx842_powernv_alg = {
.cra_driver_name = "842-nx",
.cra_priority = 300,
.cra_flags = CRYPTO_ALG_TYPE_COMPRESS,
- .cra_ctxsize = sizeof(struct nx842_crypto_ctx),
+ .cra_ctxsize = struct_size_t(struct nx842_crypto_ctx, header.group,
+ NX842_CRYPTO_GROUP_MAX),
.cra_module = THIS_MODULE,
.cra_init = nx842_powernv_crypto_init,
.cra_exit = nx842_crypto_exit,
diff --git a/drivers/crypto/nx/nx-common-pseries.c b/drivers/crypto/nx/nx-common-pseries.c
index 35f2d0d8507e..fdf328eab6fc 100644
--- a/drivers/crypto/nx/nx-common-pseries.c
+++ b/drivers/crypto/nx/nx-common-pseries.c
@@ -1018,7 +1018,8 @@ static struct crypto_alg nx842_pseries_alg = {
.cra_driver_name = "842-nx",
.cra_priority = 300,
.cra_flags = CRYPTO_ALG_TYPE_COMPRESS,
- .cra_ctxsize = sizeof(struct nx842_crypto_ctx),
+ .cra_ctxsize = struct_size_t(struct nx842_crypto_ctx, header.group,
+ NX842_CRYPTO_GROUP_MAX),
.cra_module = THIS_MODULE,
.cra_init = nx842_pseries_crypto_init,
.cra_exit = nx842_crypto_exit,
--
Kees Cook