Harden HMAC error paths: fix resource leaks, state bugs, and missing cleansing#3081
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Harden HMAC error paths: fix resource leaks, state bugs, and missing cleansing#3081
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sgmenda
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nebeid
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AWS-LC PR: aws/aws-lc#3081 The HMAC hardening PR adds OPENSSL_cleanse(tmp, sizeof(tmp)) to HMAC_Final's exit path. Add the existing OPENSSL_cleanse_ov override to both HMAC_Final verification calls so SAW can reason about the new memory write.
nebeid
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AWS-LC PR: aws/aws-lc#3081 The HMAC hardening PR adds OPENSSL_cleanse(tmp, sizeof(tmp)) to HMAC_Final's exit path. Add the existing OPENSSL_cleanse_ov override to both HMAC_Final verification calls so SAW can reason about the new memory write.
nebeid
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geedo0
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Description of changes:
Tightens up error handling across the HMAC implementation:
p_hmac.c:hmac_copyerror paths were leaking the HMAC context and key, and leftdst->dataas a dangling pointer.hmac_cleanupdidn't guard against NULL and wasn't cleansing the embedded HMAC_CTX.hmac.c(HMAC_Init_ex): Re-initializing a context that was in theIN_PROGRESSstate (same key/md, no-op path) resetmd_ctxbut forgot to transition the state back toINIT_NO_DATA.hmac.c(HMAC_Final): Sensitive intermediate inner hash (tmp) wasn't being cleansed on exit. On error, the context was left in a partially-modified state instead of being cleaned up.hmac.c(HMAC_get_precomputed_key): Invariant checks relied solely onassert(), meaning they silently disappeared in release builds. Replaced with real error returns +OPENSSL_cleanseof partial output.hmac.c(HMAC_Init): Negativekey_len(legacyintAPI) would implicitly convert to a hugesize_t, causing a buffer over-read. Added a bounds check and explicit cast.HMAC_with_precompute: Added the sameout == NULLearly-return thatHMAC()already had.Call-outs:
HMAC_Init_exstate fix is the subtlest change — the no-op re-init path was missing the state transition, which could cause downstream logic that checksstateto misbehave.HMAC_Finalnow callsHMAC_CTX_cleanup(ctx)on error, which zeros the entire context. This is more aggressive than before (caller must re-init to reuse), but the success path already required re-init (READY_NEEDS_INIT), so this should be fine in practice.HMAC_get_precomputed_keychange turns debug-only asserts into real error returns. Worth confirming we're comfortable returning 0 here even though "this should never happen."Testing:
Existing HMAC test suite. No new tests added — all changes are hardening of error/edge-case paths that existing tests exercise implicitly through the normal Init → Update → Final flow.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.