Re: [PATCH v2] KEYS: trusted: dcp: fix key_len validation and calc_blob_len() return type

[Richard Weinberger <richard@sigma-star.at>]

On Sonntag, 19. Juli 2026 18:39 'Fabrice Derepas' via upstream wrote:
> Two correctness and type-hygiene issues exist in the DCP trusted keys
> implementation.
> 
> First, trusted_dcp_unseal() reads p->key_len from a user-supplied blob
> without checking if it exceeds MAX_KEY_SIZE.  If a crafted blob provides
> a payload_len larger than 128, the subsequent do_aead_crypto() call
> writes past the end of the p->key array into the adjacent p->blob
> buffer within the same struct trusted_key_payload -- the caller's own
> input, not unrelated kernel memory.  While not exploitable, this
> violates strict array bounds and triggers static analyzers.  Fix this by adding a validation check against
> MIN_KEY_SIZE and MAX_KEY_SIZE immediately after reading the length,
> matching the checks already done in trusted_core.c.
> 
> Second, calc_blob_len() calculates a sum in size_t that truncates to
> unsigned int on 64-bit platforms.  Because the DCP hardware is only
> present on 32-bit i.MX SoC platforms, size_t and unsigned int are
> functionally equivalent in production, making this truncation harmless in
> practice.  Nevertheless, updating the return type to size_t (and
> subsequently updating 'blen' in the seal/unseal paths) resolves
> type-narrowing warnings and improves overall code hygiene.
> 
> Fixes: 2e8a0f40a39c ("KEYS: trusted: Introduce NXP DCP-backed trusted keys")
> Signed-off-by: Fabrice Derepas <fabrice.derepas@canonical.com>

Reviewed-by: Richard Weinberger <richard@nod.at>

Thanks,
//richard

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