libgcrypt/libgcrypt-jitterentropy-3.4.0.patch

Index: libgcrypt-1.10.0/random/jitterentropy-base.c
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-base.c
+++ libgcrypt-1.10.0/random/jitterentropy-base.c
@@ -42,7 +42,7 @@
 		      * require consumer to be updated (as long as this number
 		      * is zero, the API is not considered stable and can
 		      * change without a bump of the major version) */
-#define MINVERSION 3 /* API compatible, ABI may change, functional
+#define MINVERSION 4 /* API compatible, ABI may change, functional
 		      * enhancements only, consumer can be left unchanged if
 		      * enhancements are not considered */
 #define PATCHLEVEL 0 /* API / ABI compatible, no functional changes, no
@@ -200,29 +200,38 @@ ssize_t jent_read_entropy(struct rand_da
 			tocopy = (DATA_SIZE_BITS / 8);
 		else
 			tocopy = len;
-		memcpy(p, &ec->data, tocopy);
+
+		jent_read_random_block(ec, p, tocopy);
 
 		len -= tocopy;
 		p += tocopy;
 	}
 
 	/*
-	 * To be on the safe side, we generate one more round of entropy
-	 * which we do not give out to the caller. That round shall ensure
-	 * that in case the calling application crashes, memory dumps, pages
-	 * out, or due to the CPU Jitter RNG lingering in memory for long
-	 * time without being moved and an attacker cracks the application,
-	 * all he reads in the entropy pool is a value that is NEVER EVER
-	 * being used for anything. Thus, he does NOT see the previous value
-	 * that was returned to the caller for cryptographic purposes.
+	 * Enhanced backtracking support: At this point, the hash state
+	 * contains the digest of the previous Jitter RNG collection round
+	 * which is inserted there by jent_read_random_block with the SHA
+	 * update operation. At the current code location we completed
+	 * one request for a caller and we do not know how long it will
+	 * take until a new request is sent to us. To guarantee enhanced
+	 * backtracking resistance at this point (i.e. ensure that an attacker
+	 * cannot obtain information about prior random numbers we generated),
+	 * but still stirring the hash state with old data the Jitter RNG
+	 * obtains a new message digest from its state and re-inserts it.
+	 * After this operation, the Jitter RNG state is still stirred with
+	 * the old data, but an attacker who gets access to the memory after
+	 * this point cannot deduce the random numbers produced by the
+	 * Jitter RNG prior to this point.
 	 */
 	/*
-	 * If we use secured memory, do not use that precaution as the secure
-	 * memory protects the entropy pool. Moreover, note that using this
-	 * call reduces the speed of the RNG by up to half
+	 * If we use secured memory, where backtracking support may not be
+	 * needed because the state is protected in a different method,
+	 * it is permissible to drop this support. But strongly weigh the
+	 * pros and cons considering that the SHA3 operation is not that
+	 * expensive.
 	 */
 #ifndef JENT_CPU_JITTERENTROPY_SECURE_MEMORY
-	jent_random_data(ec);
+	jent_read_random_block(ec, NULL, 0);
 #endif
 
 err:
@@ -379,6 +388,7 @@ static struct rand_data
 *jent_entropy_collector_alloc_internal(unsigned int osr, unsigned int flags)
 {
 	struct rand_data *entropy_collector;
+	uint32_t memsize = 0;
 
 	/*
 	 * Requesting disabling and forcing of internal timer
@@ -405,7 +415,7 @@ static struct rand_data
 		return NULL;
 
 	if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) {
-		uint32_t memsize = jent_memsize(flags);
+		memsize = jent_memsize(flags);
 
 		entropy_collector->mem = _gcry_calloc (1, memsize);
 
@@ -431,13 +441,19 @@ static struct rand_data
 		entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
 	}
 
+	if (sha3_alloc(&entropy_collector->hash_state))
+		goto err;
+
+	/* Initialize the hash state */
+	sha3_256_init(entropy_collector->hash_state);
+
 	/* verify and set the oversampling rate */
 	if (osr < JENT_MIN_OSR)
 		osr = JENT_MIN_OSR;
 	entropy_collector->osr = osr;
 	entropy_collector->flags = flags;
 
-	if (jent_fips_enabled() || (flags & JENT_FORCE_FIPS))
+	if ((flags & JENT_FORCE_FIPS) || jent_fips_enabled())
 		entropy_collector->fips_enabled = 1;
 
 	/* Initialize the APT */
@@ -469,7 +485,7 @@ static struct rand_data
 
 err:
 	if (entropy_collector->mem != NULL)
-		jent_zfree(entropy_collector->mem, JENT_MEMORY_SIZE);
+		jent_zfree(entropy_collector->mem, memsize);
 	jent_zfree(entropy_collector, sizeof(struct rand_data));
 	return NULL;
 }
@@ -511,6 +527,7 @@ JENT_PRIVATE_STATIC
 void jent_entropy_collector_free(struct rand_data *entropy_collector)
 {
 	if (entropy_collector != NULL) {
+		sha3_dealloc(entropy_collector->hash_state);
 		jent_notime_disable(entropy_collector);
 		if (entropy_collector->mem != NULL) {
 			jent_zfree(entropy_collector->mem,
@@ -664,6 +681,7 @@ static inline int jent_entropy_init_comm
 	int ret;
 
 	jent_notime_block_switch();
+	jent_health_cb_block_switch();
 
 	if (sha3_tester())
 		return EHASH;
@@ -710,6 +728,8 @@ int jent_entropy_init_ex(unsigned int os
 	if (ret)
 		return ret;
 
+	ret = ENOTIME;
+
 	/* Test without internal timer unless caller does not want it */
 	if (!(flags & JENT_FORCE_INTERNAL_TIMER))
 		ret = jent_time_entropy_init(osr,
@@ -732,3 +752,9 @@ int jent_entropy_switch_notime_impl(stru
 	return jent_notime_switch(new_thread);
 }
 #endif
+
+JENT_PRIVATE_STATIC
+int jent_set_fips_failure_callback(jent_fips_failure_cb cb)
+{
+	return jent_set_fips_failure_callback_internal(cb);
+}
Index: libgcrypt-1.10.0/random/jitterentropy-gcd.c
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-gcd.c
+++ libgcrypt-1.10.0/random/jitterentropy-gcd.c
@@ -113,12 +113,8 @@ int jent_gcd_analyze(uint64_t *delta_his
 		goto out;
 	}
 
-	/*
-	 * Ensure that we have variations in the time stamp below 100 for at
-	 * least 10% of all checks -- on some platforms, the counter increments
-	 * in multiples of 100, but not always
-	 */
-	if (running_gcd >= 100) {
+	/* Set a sensible maximum value. */
+	if (running_gcd >= UINT32_MAX / 2) {
 		ret = ECOARSETIME;
 		goto out;
 	}
Index: libgcrypt-1.10.0/random/jitterentropy-health.c
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-health.c
+++ libgcrypt-1.10.0/random/jitterentropy-health.c
@@ -19,9 +19,24 @@
  * DAMAGE.
  */
 
-#include "jitterentropy.h"
 #include "jitterentropy-health.h"
 
+static jent_fips_failure_cb fips_cb = NULL;
+static int jent_health_cb_switch_blocked = 0;
+
+void jent_health_cb_block_switch(void)
+{
+	jent_health_cb_switch_blocked = 1;
+}
+
+int jent_set_fips_failure_callback_internal(jent_fips_failure_cb cb)
+{
+	if (jent_health_cb_switch_blocked)
+		return -EAGAIN;
+	fips_cb = cb;
+	return 0;
+}
+
 /***************************************************************************
  * Lag Predictor Test
  *
@@ -434,5 +449,9 @@ unsigned int jent_health_failure(struct
 	if (!ec->fips_enabled)
 		return 0;
 
+	if (fips_cb && ec->health_failure) {
+		fips_cb(ec, ec->health_failure);
+	}
+
 	return ec->health_failure;
 }
Index: libgcrypt-1.10.0/random/jitterentropy-health.h
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-health.h
+++ libgcrypt-1.10.0/random/jitterentropy-health.h
@@ -20,11 +20,16 @@
 #ifndef JITTERENTROPY_HEALTH_H
 #define JITTERENTROPY_HEALTH_H
 
+#include "jitterentropy.h"
+
 #ifdef __cplusplus
 extern "C"
 {
 #endif
 
+void jent_health_cb_block_switch(void);
+int jent_set_fips_failure_callback_internal(jent_fips_failure_cb cb);
+
 static inline uint64_t jent_delta(uint64_t prev, uint64_t next)
 {
 	return (next - prev);
Index: libgcrypt-1.10.0/random/jitterentropy-noise.c
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-noise.c
+++ libgcrypt-1.10.0/random/jitterentropy-noise.c
@@ -33,7 +33,7 @@
  * Update of the loop count used for the next round of
  * an entropy collection.
  *
- * @ec [in] entropy collector struct -- may be NULL
+ * @ec [in] entropy collector struct
  * @bits [in] is the number of low bits of the timer to consider
  * @min [in] is the number of bits we shift the timer value to the right at
  *	     the end to make sure we have a guaranteed minimum value
@@ -61,16 +61,13 @@ static uint64_t jent_loop_shuffle(struct
 	 * Mix the current state of the random number into the shuffle
 	 * calculation to balance that shuffle a bit more.
 	 */
-	if (ec) {
-		jent_get_nstime_internal(ec, &time);
-		time ^= ec->data[0];
-	}
+	jent_get_nstime_internal(ec, &time);
 
 	/*
 	 * We fold the time value as much as possible to ensure that as many
 	 * bits of the time stamp are included as possible.
 	 */
-	for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) {
+	for (i = 0; (((sizeof(time) << 3) + bits - 1) / bits) > i; i++) {
 		shuffle ^= time & mask;
 		time = time >> bits;
 	}
@@ -91,11 +88,11 @@ static uint64_t jent_loop_shuffle(struct
  * This function injects the individual bits of the time value into the
  * entropy pool using a hash.
  *
- * @ec [in] entropy collector struct -- may be NULL
- * @time [in] time stamp to be injected
+ * @ec [in] entropy collector struct
+ * @time [in] time delta to be injected
  * @loop_cnt [in] if a value not equal to 0 is set, use the given value as
  *		  number of loops to perform the hash operation
- * @stuck [in] Is the time stamp identified as stuck?
+ * @stuck [in] Is the time delta identified as stuck?
  *
  * Output:
  * updated hash context
@@ -104,17 +101,19 @@ static void jent_hash_time(struct rand_d
 			   uint64_t loop_cnt, unsigned int stuck)
 {
 	HASH_CTX_ON_STACK(ctx);
-	uint8_t itermediary[SHA3_256_SIZE_DIGEST];
+	uint8_t intermediary[SHA3_256_SIZE_DIGEST];
 	uint64_t j = 0;
-	uint64_t hash_loop_cnt;
 #define MAX_HASH_LOOP 3
 #define MIN_HASH_LOOP 0
 
 	/* Ensure that macros cannot overflow jent_loop_shuffle() */
 	BUILD_BUG_ON((MAX_HASH_LOOP + MIN_HASH_LOOP) > 63);
-	hash_loop_cnt =
+	uint64_t hash_loop_cnt =
 		jent_loop_shuffle(ec, MAX_HASH_LOOP, MIN_HASH_LOOP);
 
+	/* Use the memset to shut up valgrind */
+	memset(intermediary, 0, sizeof(intermediary));
+
 	sha3_256_init(&ctx);
 
 	/*
@@ -125,35 +124,54 @@ static void jent_hash_time(struct rand_d
 		hash_loop_cnt = loop_cnt;
 
 	/*
-	 * This loop basically slows down the SHA-3 operation depending
-	 * on the hash_loop_cnt. Each iteration of the loop generates the
-	 * same result.
+	 * This loop fills a buffer which is injected into the entropy pool.
+	 * The main reason for this loop is to execute something over which we
+	 * can perform a timing measurement. The injection of the resulting
+	 * data into the pool is performed to ensure the result is used and
+	 * the compiler cannot optimize the loop away in case the result is not
+	 * used at all. Yet that data is considered "additional information"
+	 * considering the terminology from SP800-90A without any entropy.
+	 *
+	 * Note, it does not matter which or how much data you inject, we are
+	 * interested in one Keccack1600 compression operation performed with
+	 * the sha3_final.
 	 */
 	for (j = 0; j < hash_loop_cnt; j++) {
-		sha3_update(&ctx, ec->data, SHA3_256_SIZE_DIGEST);
-		sha3_update(&ctx, (uint8_t *)&time, sizeof(uint64_t));
+		sha3_update(&ctx, intermediary, sizeof(intermediary));
+		sha3_update(&ctx, (uint8_t *)&ec->rct_count,
+			    sizeof(ec->rct_count));
+		sha3_update(&ctx, (uint8_t *)&ec->apt_cutoff,
+			    sizeof(ec->apt_cutoff));
+		sha3_update(&ctx, (uint8_t *)&ec->apt_observations,
+			    sizeof(ec->apt_observations));
+		sha3_update(&ctx, (uint8_t *)&ec->apt_count,
+			    sizeof(ec->apt_count));
+		sha3_update(&ctx,(uint8_t *) &ec->apt_base,
+			    sizeof(ec->apt_base));
 		sha3_update(&ctx, (uint8_t *)&j, sizeof(uint64_t));
+		sha3_final(&ctx, intermediary);
+	}
 
-		/*
-		 * If the time stamp is stuck, do not finally insert the value
-		 * into the entropy pool. Although this operation should not do
-		 * any harm even when the time stamp has no entropy, SP800-90B
-		 * requires that any conditioning operation to have an identical
-		 * amount of input data according to section 3.1.5.
-		 */
+	/*
+	 * Inject the data from the previous loop into the pool. This data is
+	 * not considered to contain any entropy, but it stirs the pool a bit.
+	 */
+	sha3_update(ec->hash_state, intermediary, sizeof(intermediary));
 
-		/*
-		 * The sha3_final operations re-initialize the context for the
-		 * next loop iteration.
-		 */
-		if (stuck || (j < hash_loop_cnt - 1))
-			sha3_final(&ctx, itermediary);
-		else
-			sha3_final(&ctx, ec->data);
-	}
+	/*
+	 * Insert the time stamp into the hash context representing the pool.
+	 *
+	 * If the time stamp is stuck, do not finally insert the value into the
+	 * entropy pool. Although this operation should not do any harm even
+	 * when the time stamp has no entropy, SP800-90B requires that any
+	 * conditioning operation to have an identical amount of input data
+	 * according to section 3.1.5.
+	 */
+	if (!stuck)
+		sha3_update(ec->hash_state, (uint8_t *)&time, sizeof(uint64_t));
 
 	jent_memset_secure(&ctx, SHA_MAX_CTX_SIZE);
-	jent_memset_secure(itermediary, sizeof(itermediary));
+	jent_memset_secure(intermediary, sizeof(intermediary));
 }
 
 #define MAX_ACC_LOOP_BIT 7
@@ -184,13 +202,12 @@ static inline uint32_t xoshiro128starsta
 
 static void jent_memaccess(struct rand_data *ec, uint64_t loop_cnt)
 {
-	uint64_t i = 0;
+	uint64_t i = 0, time = 0;
 	union {
 		uint32_t u[4];
 		uint8_t b[sizeof(uint32_t) * 4];
 	} prngState = { .u = {0x8e93eec0, 0xce65608a, 0xa8d46b46, 0xe83cef69} };
 	uint32_t addressMask;
-        uint64_t acc_loop_cnt;
 
 	if (NULL == ec || NULL == ec->mem)
 		return;
@@ -199,7 +216,7 @@ static void jent_memaccess(struct rand_d
 
 	/* Ensure that macros cannot overflow jent_loop_shuffle() */
 	BUILD_BUG_ON((MAX_ACC_LOOP_BIT + MIN_ACC_LOOP_BIT) > 63);
-	acc_loop_cnt =
+	uint64_t acc_loop_cnt =
 		jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT);
 
 	/*
@@ -213,8 +230,10 @@ static void jent_memaccess(struct rand_d
 	 * "per-update: timing, it gets you mostly independent "per-update"
 	 * timing, so we can now benefit from the Central Limit Theorem!
 	 */
-	for (i = 0; i < sizeof(prngState); i++)
-		prngState.b[i] ^= ec->data[i];
+	for (i = 0; i < sizeof(prngState); i++) {
+		jent_get_nstime_internal(ec, &time);
+		prngState.b[i] ^= (uint8_t)(time & 0xff);
+	}
 
 	/*
 	 * testing purposes -- allow test app to set the counter, not
@@ -358,21 +377,21 @@ unsigned int jent_measure_jitter(struct
 
 /**
  * Generator of one 256 bit random number
- * Function fills rand_data->data
+ * Function fills rand_data->hash_state
  *
  * @ec [in] Reference to entropy collector
  */
 void jent_random_data(struct rand_data *ec)
 {
-	unsigned int k = 0, safety_factor = ENTROPY_SAFETY_FACTOR;
+	unsigned int k = 0, safety_factor = 0;
 
-	if (!ec->fips_enabled)
-		safety_factor = 0;
+	if (ec->fips_enabled)
+		safety_factor = ENTROPY_SAFETY_FACTOR;
 
 	/* priming of the ->prev_time value */
 	jent_measure_jitter(ec, 0, NULL);
 
-	while (1) {
+	while (!jent_health_failure(ec)) {
 		/* If a stuck measurement is received, repeat measurement */
 		if (jent_measure_jitter(ec, 0, NULL))
 			continue;
@@ -385,3 +404,22 @@ void jent_random_data(struct rand_data *
 			break;
 	}
 }
+
+void jent_read_random_block(struct rand_data *ec, char *dst, size_t dst_len)
+{
+	uint8_t jent_block[SHA3_256_SIZE_DIGEST];
+
+	BUILD_BUG_ON(SHA3_256_SIZE_DIGEST != (DATA_SIZE_BITS / 8));
+
+	/* The final operation automatically re-initializes the ->hash_state */
+	sha3_final(ec->hash_state, jent_block);
+	if (dst_len)
+		memcpy(dst, jent_block, dst_len);
+
+	/*
+	 * Stir the new state with the data from the old state - the digest
+	 * of the old data is not considered to have entropy.
+	 */
+	sha3_update(ec->hash_state, jent_block, sizeof(jent_block));
+	jent_memset_secure(jent_block, sizeof(jent_block));
+}
Index: libgcrypt-1.10.0/random/jitterentropy-noise.h
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-noise.h
+++ libgcrypt-1.10.0/random/jitterentropy-noise.h
@@ -31,6 +31,7 @@ unsigned int jent_measure_jitter(struct
 				 uint64_t loop_cnt,
 				 uint64_t *ret_current_delta);
 void jent_random_data(struct rand_data *ec);
+void jent_read_random_block(struct rand_data *ec, char *dst, size_t dst_len);
 
 #ifdef __cplusplus
 }
Index: libgcrypt-1.10.0/random/jitterentropy-sha3.c
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-sha3.c
+++ libgcrypt-1.10.0/random/jitterentropy-sha3.c
@@ -19,6 +19,7 @@
  */
 
 #include "jitterentropy-sha3.h"
+#include "jitterentropy.h"
 
 /***************************************************************************
  * Message Digest Implementation
@@ -380,3 +381,23 @@ int sha3_tester(void)
 
 	return 0;
 }
+
+int sha3_alloc(void **hash_state)
+{
+	struct sha_ctx *tmp;
+
+	tmp = jent_zalloc(SHA_MAX_CTX_SIZE);
+	if (!tmp)
+		return 1;
+
+	*hash_state = tmp;
+
+	return 0;
+}
+
+void sha3_dealloc(void *hash_state)
+{
+	struct sha_ctx *ctx = (struct sha_ctx *)hash_state;
+
+	jent_zfree(ctx, SHA_MAX_CTX_SIZE);
+}
Index: libgcrypt-1.10.0/random/jitterentropy-sha3.h
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-sha3.h
+++ libgcrypt-1.10.0/random/jitterentropy-sha3.h
@@ -47,6 +47,8 @@ struct sha_ctx {
 void sha3_256_init(struct sha_ctx *ctx);
 void sha3_update(struct sha_ctx *ctx, const uint8_t *in, size_t inlen);
 void sha3_final(struct sha_ctx *ctx, uint8_t *digest);
+int sha3_alloc(void **hash_state);
+void sha3_dealloc(void *hash_state);
 int sha3_tester(void);
 
 #ifdef __cplusplus
Index: libgcrypt-1.10.0/random/jitterentropy-timer.c
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-timer.c
+++ libgcrypt-1.10.0/random/jitterentropy-timer.c
@@ -202,8 +202,8 @@ int jent_notime_enable(struct rand_data
 	if (jent_force_internal_timer || (flags & JENT_FORCE_INTERNAL_TIMER)) {
 		/* Self test not run yet */
 		if (!jent_force_internal_timer &&
-		    jent_time_entropy_init(flags | JENT_FORCE_INTERNAL_TIMER,
-					   ec->osr))
+		    jent_time_entropy_init(ec->osr,
+					   flags | JENT_FORCE_INTERNAL_TIMER))
 			return EHEALTH;
 
 		ec->enable_notime = 1;
Index: libgcrypt-1.10.0/random/jitterentropy.h
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy.h
+++ libgcrypt-1.10.0/random/jitterentropy.h
@@ -49,7 +49,7 @@
  ***************************************************************************/
 
 /*
- * Enable timer-less timer support
+ * Enable timer-less timer support with JENT_CONF_ENABLE_INTERNAL_TIMER
  *
  * In case the hardware is identified to not provide a high-resolution time
  * stamp, this option enables a built-in high-resolution time stamp mechanism.
@@ -166,7 +166,7 @@ struct rand_data
 	 * of the RNG are marked as SENSITIVE. A user must not
 	 * access that information while the RNG executes its loops to
 	 * calculate the next random value. */
-	uint8_t data[SHA3_256_SIZE_DIGEST]; /* SENSITIVE Actual random number */
+	void *hash_state;		/* SENSITIVE hash state entropy pool */
 	uint64_t prev_time;		/* SENSITIVE Previous time stamp */
 #define DATA_SIZE_BITS (SHA3_256_SIZE_DIGEST_BITS)
 
@@ -378,28 +378,34 @@ int jent_entropy_init(void);
 JENT_PRIVATE_STATIC
 int jent_entropy_init_ex(unsigned int osr, unsigned int flags);
 
+/*
+ * Set a callback to run on health failure in FIPS mode.
+ * This function will take an action determined by the caller.
+ */
+typedef void (*jent_fips_failure_cb)(struct rand_data *ec,
+				     unsigned int health_failure);
+JENT_PRIVATE_STATIC
+int jent_set_fips_failure_callback(jent_fips_failure_cb cb);
+
 /* return version number of core library */
 JENT_PRIVATE_STATIC
 unsigned int jent_version(void);
 
-#ifdef JENT_CONF_ENABLE_INTERNAL_TIMER
 /* Set a different thread handling logic for the notimer support */
 JENT_PRIVATE_STATIC
 int jent_entropy_switch_notime_impl(struct jent_notime_thread *new_thread);
-#endif
 
 /* -- END of Main interface functions -- */
 
 /* -- BEGIN timer-less threading support functions to prevent code dupes -- */
 
-struct jent_notime_ctx {
 #ifdef JENT_CONF_ENABLE_INTERNAL_TIMER
+
+struct jent_notime_ctx {
 	pthread_attr_t notime_pthread_attr;	/* pthreads library */
 	pthread_t notime_thread_id;		/* pthreads thread ID */
-#endif
 };
 
-#ifdef JENT_CONF_ENABLE_INTERNAL_TIMER
 
 JENT_PRIVATE_STATIC
 int jent_notime_init(void **ctx);
Index: libgcrypt-1.10.0/random/jitterentropy-base-user.h
===================================================================
--- libgcrypt-1.10.0.orig/random/jitterentropy-base-user.h
+++ libgcrypt-1.10.0/random/jitterentropy-base-user.h
@@ -213,12 +213,12 @@ static inline void jent_get_cachesize(lo
 		ext = strstr(buf, "K");
 		if (ext) {
 			shift = 10;
-			ext = '\0';
+			*ext = '\0';
 		} else {
 			ext = strstr(buf, "M");
 			if (ext) {
 				shift = 20;
-				ext = '\0';
+				*ext = '\0';
 			}
 		}