A long time ago (in 2.6.9 and 2.4.28), crypto_free_tfm() started zeroing
"alg->cra_ctxsize" bytes before freeing a crypto_tfm:
| commit 94ab49d18f69a816561ae199e05daab709ba912e (from full-history-linux)
| Author: David S. Miller <davem@xxxxxxxxxxxxxxxxxx>
| Date: Tue Sep 14 08:21:40 2004 -0700
|
| [CRYPTO]: Zero out tfm before freeing in crypto_free_tfm().
|
| Based upon discussions with Ulrich Kuehn
| (ukuehn@xxxxxxx)
|
| Signed-off-by: James Morris <jmorris@xxxxxxxxxx>
| Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
|
| diff --git a/crypto/api.c b/crypto/api.c
| index 6f0e625..394169a 100644
| --- a/crypto/api.c
| +++ b/crypto/api.c
| @@ -155,8 +155,12 @@ out:
|
| void crypto_free_tfm(struct crypto_tfm *tfm)
| {
| + struct crypto_alg *alg = tfm->__crt_alg;
| + int size = sizeof(*tfm) + alg->cra_ctxsize;
| +
| crypto_exit_ops(tfm);
| - crypto_alg_put(tfm->__crt_alg);
| + crypto_alg_put(alg);
| + memset(tfm, 0, size);
| kfree(tfm);
| }
However, in the mean time, the allocation mechanism for crypto_tfm objects has
been changed twice, by:
1. commit fbdae9f3e7fb57c07cb0d973f113eb25da2e8ff2 ("[CRYPTO] Ensure cit_iv
is aligned correctly"), which replaced "alg->cra_ctxsize" by
"crypto_ctxsize(alg, flags)" in crypto_alloc_tfm(),
2. commit 7b0bac64cd5b74d6f1147524c26216de13a501fd ("crypto: api - Rebirth of
crypto_alloc_tfm"), which introduced the alternative crypto_create_tfm(),
where the memory requirements are based on
"frontend->extsize(alg, frontend)" instead of "alg->cra_ctxsize".
Fortunately (for all current transforms under crypto/), it seems that
"crypto_ctxsize(alg, flags)" and "frontend->extsize(alg, frontend)" are always
at least as large as "alg->cra_ctxsize". But still,
(a) this may leak key information in the few cases where the actual key size
is larger than "alg->cra_ctxsize",
(b) this may change in the future, causing memory corruption.
With kind regards,
Geert Uytterhoeven
Software Architect
Sony Techsoft Centre Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium
Phone: +32 (0)2 700 8453
Fax: +32 (0)2 700 8622
E-mail: Geert.Uytterhoeven@xxxxxxxxxxx
Internet: http://www.sony-europe.com/
A division of Sony Europe (Belgium) N.V.
VAT BE 0413.825.160 · RPR Brussels
Fortis · BIC GEBABEBB · IBAN BE41293037680010
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