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Fix bad free in skein code 

Clang's static analyzer found a bad free caused by skein_mac_atomic().
It will allocate a context on the stack and then pass it to
skein_final(), which attempts to free it. Upon inspection,
skein_digest_atomic() also has the same problem.

These functions were created to match the OpenSolaris ICP API, so I was
curious how we avoided this in other providers and looked at the SHA2
code. It appears that SHA2 has a SHA2Final() helper function that is
called by the exported sha2_mac_final()/sha2_digest_final() as well as
the sha2_mac_atomic() and sha2_digest_atomic() functions. The real work
is done in SHA2Final() while some checks and the free are done in
sha2_mac_final()/sha2_digest_final().

We fix the use after free in the skein code by taking inspiration from
the SHA2 code. We introduce a skein_final_nofree() that does most of the
work, and make skein_final() into a function that calls it and then
frees the memory.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13954
This commit is contained in:
Richard Yao 2022-09-27 15:36:58 -04:00 committed by GitHub
parent f7bda2de97
commit a2163a96ae
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 14 additions and 3 deletions
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17
module/icp/io/skein_mod.c
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@ -421,7 +421,7 @@ skein_update(crypto_ctx_t *ctx, crypto_data_t *data)
* Supported output digest formats are raw, uio and mblk. * Supported output digest formats are raw, uio and mblk.
*/ */
static int static int
skein_final(crypto_ctx_t *ctx, crypto_data_t *digest) skein_final_nofree(crypto_ctx_t *ctx, crypto_data_t *digest)
{ {
int error = CRYPTO_SUCCESS; int error = CRYPTO_SUCCESS;
@ -452,6 +452,17 @@ skein_final(crypto_ctx_t *ctx, crypto_data_t *digest)
else else
digest->cd_length = 0; digest->cd_length = 0;
return (error);
}
static int
skein_final(crypto_ctx_t *ctx, crypto_data_t *digest)
{
int error = skein_final_nofree(ctx, digest);
if (error == CRYPTO_BUFFER_TOO_SMALL)
return (error);
memset(SKEIN_CTX(ctx), 0, sizeof (*SKEIN_CTX(ctx))); memset(SKEIN_CTX(ctx), 0, sizeof (*SKEIN_CTX(ctx)));
kmem_free(SKEIN_CTX(ctx), sizeof (*(SKEIN_CTX(ctx)))); kmem_free(SKEIN_CTX(ctx), sizeof (*(SKEIN_CTX(ctx))));
SKEIN_CTX_LVALUE(ctx) = NULL; SKEIN_CTX_LVALUE(ctx) = NULL;
@ -485,7 +496,7 @@ skein_digest_atomic(crypto_mechanism_t *mechanism, crypto_data_t *data,
if ((error = skein_update(&ctx, data)) != CRYPTO_SUCCESS) if ((error = skein_update(&ctx, data)) != CRYPTO_SUCCESS)
goto out; goto out;
if ((error = skein_final(&ctx, data)) != CRYPTO_SUCCESS) if ((error = skein_final_nofree(&ctx, data)) != CRYPTO_SUCCESS)
goto out; goto out;
out: out:
@ -588,7 +599,7 @@ skein_mac_atomic(crypto_mechanism_t *mechanism,
if ((error = skein_update(&ctx, data)) != CRYPTO_SUCCESS) if ((error = skein_update(&ctx, data)) != CRYPTO_SUCCESS)
goto errout; goto errout;
if ((error = skein_final(&ctx, mac)) != CRYPTO_SUCCESS) if ((error = skein_final_nofree(&ctx, mac)) != CRYPTO_SUCCESS)
goto errout; goto errout;
return (CRYPTO_SUCCESS); return (CRYPTO_SUCCESS);