OPENSSL_MALLOC(3ossl)

📦

version 15.1 · 2 versions

15.1 · freebsd 15.1 (latest)
14.5 · freebsd 14.5

🌸 NAME 🌸

okay bestie, welcome to OPENSSL_MALLOC(3ossl) — the OpenSSL memory-allocation page, aka Memory allocation functions. This is the whole squad and every single name matters, so here we go:

OPENSSL_malloc_init, OPENSSL_malloc, OPENSSL_aligned_alloc, OPENSSL_zalloc, OPENSSL_realloc, OPENSSL_free
OPENSSL_clear_realloc, OPENSSL_clear_free, OPENSSL_cleanse
CRYPTO_malloc, CRYPTO_aligned_alloc, CRYPTO_zalloc, CRYPTO_realloc, CRYPTO_free
OPENSSL_strdup, OPENSSL_strndup, OPENSSL_memdup
OPENSSL_strlcpy, OPENSSL_strlcat, OPENSSL_strtoul
CRYPTO_strdup, CRYPTO_strndup
OPENSSL_mem_debug_push, OPENSSL_mem_debug_pop
CRYPTO_mem_debug_push, CRYPTO_mem_debug_pop
CRYPTO_clear_realloc, CRYPTO_clear_free
CRYPTO_malloc_fn, CRYPTO_realloc_fn, CRYPTO_free_fn
CRYPTO_get_mem_functions, CRYPTO_set_mem_functions
CRYPTO_get_alloc_counts, CRYPTO_set_mem_debug, CRYPTO_mem_ctrl
CRYPTO_mem_leaks, CRYPTO_mem_leaks_fp, CRYPTO_mem_leaks_cb
OPENSSL_MALLOC_FAILURES, OPENSSL_MALLOC_FD

✨ SYNOPSIS ✨

        #include <openssl/crypto.h>

        int OPENSSL_malloc_init(void);

        void *OPENSSL_malloc(size_t num);
        void *OPENSSL_aligned_alloc(size_t num, size_t alignment, void **freeptr);
        void *OPENSSL_zalloc(size_t num);
        void *OPENSSL_realloc(void *addr, size_t num);
        void OPENSSL_free(void *addr);
        char *OPENSSL_strdup(const char *str);
        char *OPENSSL_strndup(const char *str, size_t s);
        size_t OPENSSL_strlcat(char *dst, const char *src, size_t size);
        size_t OPENSSL_strlcpy(char *dst, const char *src, size_t size);
        int OPENSSL_strtoul(char *src, char **endptr, int base, unsigned long *num);
        void *OPENSSL_memdup(void *data, size_t s);
        void *OPENSSL_clear_realloc(void *p, size_t old_len, size_t num);
        void OPENSSL_clear_free(void *str, size_t num);
        void OPENSSL_cleanse(void *ptr, size_t len);

        void *CRYPTO_malloc(size_t num, const char *file, int line);
        void *CRYPTO_aligned_alloc(size_t num, size_t align, void **freeptr,
                                   const char *file, int line);
        void *CRYPTO_zalloc(size_t num, const char *file, int line);
        void *CRYPTO_realloc(void *p, size_t num, const char *file, int line);
        void CRYPTO_free(void *str, const char *, int);
        char *CRYPTO_strdup(const char *p, const char *file, int line);
        char *CRYPTO_strndup(const char *p, size_t num, const char *file, int line);
        void *CRYPTO_clear_realloc(void *p, size_t old_len, size_t num,
                                   const char *file, int line);
        void CRYPTO_clear_free(void *str, size_t num, const char *, int);

        typedef void *(*CRYPTO_malloc_fn)(size_t num, const char *file, int line);
        typedef void *(*CRYPTO_realloc_fn)(void *addr, size_t num, const char *file,
                                           int line);
        typedef void (*CRYPTO_free_fn)(void *addr, const char *file, int line);
        void CRYPTO_get_mem_functions(CRYPTO_malloc_fn *malloc_fn,
                                      CRYPTO_realloc_fn *realloc_fn,
                                      CRYPTO_free_fn *free_fn);
        int CRYPTO_set_mem_functions(CRYPTO_malloc_fn malloc_fn,
                                     CRYPTO_realloc_fn realloc_fn,
                                     CRYPTO_free_fn free_fn);

        void CRYPTO_get_alloc_counts(int *mcount, int *rcount, int *fcount);

        env OPENSSL_MALLOC_FAILURES=... <application>
        env OPENSSL_MALLOC_FD=... <application>

The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

        int CRYPTO_mem_leaks(BIO *b);
        int CRYPTO_mem_leaks_fp(FILE *fp);
        int CRYPTO_mem_leaks_cb(int (*cb)(const char *str, size_t len, void *u),
                                void *u);

        int CRYPTO_set_mem_debug(int onoff);
        int CRYPTO_mem_ctrl(int mode);
        int OPENSSL_mem_debug_push(const char *info);
        int OPENSSL_mem_debug_pop(void);
        int CRYPTO_mem_debug_push(const char *info, const char *file, int line);
        int CRYPTO_mem_debug_pop(void);

🌈 DESCRIPTION 🌈

OpenSSL memory allocation is handled by the OPENSSL_xxx API. These are generally macros that add the standard C __FILE__ and __LINE__ parameters and call a lower-level CRYPTO_xxx API. Some functions do not add those parameters, but exist for consistency.

OPENSSL_malloc_init() does nothing and does not need to be called. It is included for compatibility with older versions of OpenSSL. literally just vibes, bestie.

OPENSSL_malloc(), OPENSSL_realloc(), and OPENSSL_free() are like the C malloc(), realloc(), and free() functions. OPENSSL_zalloc() calls memset() to zero the memory before returning.

🎀 aligned alloc tea

OPENSSL_aligned_alloc() operates just as OPENSSL_malloc does, but it allows for the caller to specify an alignment value, for instances in which the default alignment of malloc is insufficient for the callers needs. Note, the alignment value must be a power of 2, and the size specified must be a multiple of the alignment.

NOTE: The call to OPENSSL_aligned_alloc() accepts a 3rd argument, freeptr which must point to a void pointer. On some platforms, there is no available library call to obtain memory allocations greater than what malloc provides. In this case, OPENSSL_aligned_alloc implements its own alignment routine, allocating additional memory and offsetting the returned pointer to be on the requested alignment boundary. In order to safely free allocations made by this method, the caller must return the value in the freeptr variable, rather than the returned pointer. 💅

🔥 sensitive memory cleanup

OPENSSL_clear_realloc() and OPENSSL_clear_free() should be used when the buffer at addr holds sensitive information. The old buffer is filled with zero's by calling OPENSSL_cleanse() before ultimately calling OPENSSL_free(). If the argument to OPENSSL_clear_free() is NULL, nothing is done.

OPENSSL_cleanse() fills ptr of size len with a string of 0's. It is useful in cases when it is needed to ensure that memory (that contains sensitive information) is overwritten (for example, before it is reclaimed, or when it is stored on stack), and such operation is not optimised out by compiler optimisations such as dead store elimination (as memset(3) may be).

Use OPENSSL_cleanse() with care if the memory is a mapping of a file. If the storage controller uses write compression, then it's possible that sensitive tail bytes will survive zeroization because the block of zeros will be compressed. If the storage controller uses wear leveling, then the old sensitive data will not be overwritten; rather, a block of 0's will be written at a new physical location. 😭

🦋 string + memory helpers

OPENSSL_strdup(), OPENSSL_strndup() and OPENSSL_memdup() are like the equivalent C functions, except that memory is allocated by calling the OPENSSL_malloc() and should be released by calling OPENSSL_free().

OPENSSL_strlcpy(), OPENSSL_strlcat() and OPENSSL_strnlen() are equivalents of the common C library functions and are provided for portability.

OPENSSL_strtoul() is a wrapper around the POSIX function strtoul, with the same behaviors listed in the POSIX documentation, with the additional behavior that it validates the input str and num parameters for not being NULL, and confirms that at least a single byte of input has been consumed in the translation, returning an error in the event that no bytes were consumed.

👑 swapping the allocators

If no allocations have been done, it is possible to "swap out" the default implementations for OPENSSL_malloc(), OPENSSL_realloc() and OPENSSL_free() and replace them with alternate versions. CRYPTO_get_mem_functions() function fills in the given arguments with the function pointers for the current implementations. With CRYPTO_set_mem_functions(), you can specify a different set of functions. If any of malloc_fn, realloc_fn, or free_fn are NULL, then the function is not changed. While it's permitted to swap out only a few and not all the functions with CRYPTO_set_mem_functions(), it's recommended to swap them all out at once.

🧚 crypto-mdebug extras

If the library is built with the "crypto-mdebug" option, then one function, CRYPTO_get_alloc_counts(), and two additional environment variables, OPENSSL_MALLOC_FAILURES and OPENSSL_MALLOC_FD, are available.

The function CRYPTO_get_alloc_counts() fills in the number of times each of CRYPTO_malloc(), CRYPTO_realloc(), and CRYPTO_free() have been called, into the values pointed to by mcount, rcount, and fcount, respectively. If a pointer is NULL, then the corresponding count is not stored.

The variable OPENSSL_MALLOC_FAILURES controls how often allocations should fail. It is a set of fields separated by semicolons, which each field is a count (defaulting to zero) and an optional atsign and percentage (defaulting to 100). If the count is zero, then it lasts forever. For example, "100;@25" or "100@0;0@25" means the first 100 allocations pass, then all other allocations (until the program exits or crashes) have a 25% chance of failing. The length of the value of OPENSSL_MALLOC_FAILURES must be 256 or fewer characters.

If the variable OPENSSL_MALLOC_FD is parsed as a positive integer, then it is taken as an open file descriptor. This is used in conjunction with OPENSSL_MALLOC_FAILURES described above. For every allocation it will log details about how many allocations there have been so far, what percentage chance there is for this allocation failing, and whether it has actually failed.

The following example in classic shell syntax shows how to use this (will not work on all platforms):

         OPENSSL_MALLOC_FAILURES='200;@10'
         export OPENSSL_MALLOC_FAILURES
         OPENSSL_MALLOC_FD=3
         export OPENSSL_MALLOC_FD
         ...app invocation... 3>/tmp/log$$

💖 RETURN VALUES 💖

okay so this is the part everyone scrolls to first, and honestly? valid. here's the receipts, bestie:

OPENSSL_malloc_init(), OPENSSL_free(), OPENSSL_clear_free(), CRYPTO_free(), CRYPTO_clear_free() and CRYPTO_get_mem_functions() — these ones return no value. literally nothing. void. they do their little task and dip 😌
OPENSSL_malloc(), OPENSSL_aligned_alloc(), OPENSSL_zalloc(), OPENSSL_realloc(), OPENSSL_clear_realloc(), CRYPTO_malloc(), CRYPTO_zalloc(), CRYPTO_realloc(), CRYPTO_clear_realloc(), OPENSSL_strdup(), and OPENSSL_strndup() — these give you a pointer to the allocated memory 🎁 or NULL on error. so like, always vibe check your pointer before you use it, fr fr.
CRYPTO_set_mem_functions() — returns 1 on success or 0 on failure. and the failure is almost always because allocations have already happened 💀 like sorry bestie, the party started without you.
CRYPTO_mem_leaks(), CRYPTO_mem_leaks_fp(), CRYPTO_mem_leaks_cb(), CRYPTO_set_mem_debug(), and CRYPTO_mem_ctrl() — deprecated and they're no-ops that always return -1. not them being iconically useless 🙈
OPENSSL_mem_debug_push(), OPENSSL_mem_debug_pop(), CRYPTO_mem_debug_push(), and CRYPTO_mem_debug_pop() — also deprecated, also no-ops, but these always return 0. different flavor of nothing, slay ✨

okay and now OPENSSL_strtoul() — she's the main character of this section. returns 1 on success and 0 if an error has occurred. specifically, you get 0 in these events:

if the underlying call to strtoul returned a non zero errno value 😬
if the translation did not consume the entire input string, and the passed endptr value was NULL 🚩
if no characters were consumed in the translation (empty vibes, no notes)

⚠️ big warning, do not skip this one: a success condition does not imply that the expected translation has been performed. like, success ≠ correct, iykyk. for instance, calling:

OPENSSL_strtoul("0x12345", &endptr, 10, &num);

will result in a successful translation with num having the value 0, and *endptr = 'x'. 😭 so please, for the love of everything, validate how much data was consumed when calling this function. don't just trust the return value and walk away, bestie.

🌈 HISTORY 🌈

OPENSSL_mem_debug_push(), OPENSSL_mem_debug_pop(), CRYPTO_mem_debug_push(), CRYPTO_mem_debug_pop(), CRYPTO_mem_leaks(), CRYPTO_mem_leaks_fp(), CRYPTO_mem_leaks_cb(), CRYPTO_set_mem_debug(), CRYPTO_mem_ctrl() — all deprecated in OpenSSL 3.0. the memory-leak checking got deprecated in OpenSSL 3.0 in favor of clang's memory and leak sanitizer 🧚 (make the switch, she's better).
OPENSSL_aligned_alloc(), CRYPTO_aligned_alloc(), OPENSSL_strtoul() — these were added in OpenSSL 3.4 🎀 fresh drop, new arrivals.

👑 COPYRIGHT 👑

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

and that's the whole page, bestie 🫶 this was OPENSSL_MALLOC(3ossl), version 3.5.6, dated 2026-04-07 — go forth and allocate responsibly, and remember: check your pointers, check your endptr, and never trust a 0 that looks too good to be true 💅💖

📦 where this page comes from

freebsd 15.1: base 15.1
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms