crypto: drbg - fix maximum value checks on 32 bit systems

The maximum values for additional input string or generated blocks is
larger than 1<<32. To ensure a sensible value on 32 bit systems, return
SIZE_MAX on 32 bit systems. This value is lower than the maximum
allowed values defined in SP800-90A. The standard allow lower maximum
values, but not larger values.

SIZE_MAX - 1 is used for drbg_max_addtl to allow
drbg_healthcheck_sanity to check the enforcement of the variable
without wrapping.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/crypto/drbg.h b/include/crypto/drbg.h
index 3d8e73a1a1c7..5186f750c713 100644
--- a/include/crypto/drbg.h
+++ b/include/crypto/drbg.h
@@ -154,13 +154,26 @@ static inline size_t drbg_max_request_bytes(struct drbg_state *drbg)
 static inline size_t drbg_max_addtl(struct drbg_state *drbg)
 {
         /* SP800-90A requires 2**35 bytes additional info str / pers str */
+#if (__BITS_PER_LONG == 32)
+        /*
+         * SP800-90A allows smaller maximum numbers to be returned -- we
+         * return SIZE_MAX - 1 to allow the verification of the enforcement
+         * of this value in drbg_healthcheck_sanity.
+         */
+        return (SIZE_MAX - 1);
+#else
         return (1UL<<35);
+#endif
 }
 
 static inline size_t drbg_max_requests(struct drbg_state *drbg)
 {
         /* SP800-90A requires 2**48 maximum requests before reseeding */
+#if (__BITS_PER_LONG == 32)
+        return SIZE_MAX;
+#else
         return (1UL<<48);
+#endif
 }
 
 /*