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01f0d1ea1e
Add recallocarray(), introduced in OpenBSD 6.1, and freezero(), introduced in OpenBSD 6.2. The former is imported as-is from OpenBSD, while the latter is the non-malloc-internal branch of the same code (and also the OpenSSH portable variant). Both of these originated in OpenBSD, but have also been implemented by IllumOS, cf. https://www.illumos.org/issues/8546 Documentation for these functions is in malloc(3) upstream, the relevant parts of which were previously imported in reallocarray(3bsd). Update reallocarray(3bsd) with the changes that were introduced since, and add the relevant bits for recallocarray() and freezero(), plus aliases. [guillem@hadrons.org: Update copyright in COPYING. ] Closes: !10 Signed-off-by: Guillem Jover <guillem@hadrons.org>
296 lines
6.6 KiB
Plaintext
296 lines
6.6 KiB
Plaintext
.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $OpenBSD: malloc.3,v 1.126 2019/09/14 13:16:50 otto Exp $
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.\"
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.Dd $Mdocdate: September 14 2019 $
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.Dt REALLOCARRAY 3bsd
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.Os
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.Sh NAME
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.Nm reallocarray ,
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.Nm recallocarray ,
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.Nm freezero
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.Nd memory allocation and deallocation
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.Sh LIBRARY
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.ds str-Lb-libbsd Utility functions from BSD systems (libbsd, \-lbsd)
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.ds doc-str-Lb-libbsd \*[str-Lb-libbsd]
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.Lb libbsd
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.Sh SYNOPSIS
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.In stdlib.h
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(See
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.Xr libbsd 7
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for include usage.)
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.Ft void *
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.Fn reallocarray "void *ptr" "size_t nmemb" "size_t size"
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.Ft void *
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.Fn recallocarray "void *ptr" "size_t oldnmemb" "size_t nmemb" "size_t size"
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.Ft void
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.Fn freezero "void *ptr" "size_t size"
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.Sh DESCRIPTION
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.Pp
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Designed for safe allocation of arrays,
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the
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.Fn reallocarray
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function is similar to
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.Fn realloc
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except it operates on
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.Fa nmemb
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members of size
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.Fa size
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and checks for integer overflow in the calculation
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.Fa nmemb
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*
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.Fa size .
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.Pp
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Used for the allocation of memory holding sensitive data,
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the
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.Fn recallocarray
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function guarantees that memory becoming unallocated is explicitly
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.Em discarded ,
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meaning cached free objects are cleared with
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.Xr explicit_bzero 3 .
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.Pp
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The
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.Fn recallocarray
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function is similar to
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.Fn reallocarray
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except it ensures newly allocated memory is cleared similar to
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.Fn calloc .
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If
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.Fa ptr
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is
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.Dv NULL ,
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.Fa oldnmemb
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is ignored and the call is equivalent to
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.Fn calloc .
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If
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.Fa ptr
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is not
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.Dv NULL ,
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.Fa oldnmemb
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must be a value such that
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.Fa oldnmemb
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*
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.Fa size
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is the size of the earlier allocation that returned
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.Fa ptr ,
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otherwise the behavior is undefined.
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The
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.Fn freezero
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function is similar to the
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.Fn free
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function except it ensures memory is explicitly discarded.
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If
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.Fa ptr
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is
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.Dv NULL ,
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no action occurs.
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If
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.Fa ptr
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is not
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.Dv NULL ,
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the
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.Fa size
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argument must be equal to or smaller than the size of the earlier allocation
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that returned
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.Fa ptr .
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.Fn freezero
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guarantees the memory range starting at
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.Fa ptr
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with length
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.Fa size
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is discarded while deallocating the whole object originally allocated.
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.Sh RETURN VALUES
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The
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.Fn reallocarray
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and
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.Fn recallocarray
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functions return a pointer to the allocated space if successful; otherwise,
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a null pointer is returned and
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.Va errno
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is set to
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.Er ENOMEM .
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.Pp
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If multiplying
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.Fa nmemb
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and
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.Fa size
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results in integer overflow,
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.Fn reallocarray
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and
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.Fn recallocarray
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return
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.Dv NULL
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and set
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.Va errno
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to
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.Er ENOMEM .
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.Pp
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If
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.Fa ptr
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is not
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.Dv NULL
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and multiplying
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.Fa oldnmemb
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and
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.Fa size
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results in integer overflow
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.Fn recallocarray
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returns
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.Dv NULL
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and sets
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.Va errno
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to
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.Er EINVAL .
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.Sh IDIOMS
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Consider
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.Fn calloc
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or the extensions
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.Fn reallocarray
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and
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.Fn recallocarray
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when there is multiplication in the
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.Fa size
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argument of
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.Fn malloc
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or
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.Fn realloc .
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For example, avoid this common idiom as it may lead to integer overflow:
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.Bd -literal -offset indent
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if ((p = malloc(num * size)) == NULL)
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err(1, NULL);
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.Ed
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.Pp
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A drop-in replacement is
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.Fn reallocarray :
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.Bd -literal -offset indent
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if ((p = reallocarray(NULL, num, size)) == NULL)
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err(1, NULL);
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.Ed
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.Pp
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Alternatively,
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.Fn calloc
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may be used at the cost of initialization overhead.
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.Pp
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When using
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.Fn realloc ,
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be careful to avoid the following idiom:
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.Bd -literal -offset indent
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size += 50;
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if ((p = realloc(p, size)) == NULL)
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return (NULL);
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.Ed
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.Pp
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Do not adjust the variable describing how much memory has been allocated
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until the allocation has been successful.
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This can cause aberrant program behavior if the incorrect size value is used.
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In most cases, the above sample will also result in a leak of memory.
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As stated earlier, a return value of
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.Dv NULL
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indicates that the old object still remains allocated.
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Better code looks like this:
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.Bd -literal -offset indent
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newsize = size + 50;
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if ((newp = realloc(p, newsize)) == NULL) {
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free(p);
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p = NULL;
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size = 0;
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return (NULL);
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}
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p = newp;
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size = newsize;
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.Ed
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.Pp
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As with
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.Fn malloc ,
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it is important to ensure the new size value will not overflow;
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i.e. avoid allocations like the following:
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.Bd -literal -offset indent
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if ((newp = realloc(p, num * size)) == NULL) {
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...
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.Ed
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.Pp
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Instead, use
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.Fn reallocarray :
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.Bd -literal -offset indent
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if ((newp = reallocarray(p, num, size)) == NULL) {
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...
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.Ed
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.Pp
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Calling
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.Fn realloc
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with a
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.Dv NULL
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.Fa ptr
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is equivalent to calling
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.Fn malloc .
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Instead of this idiom:
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.Bd -literal -offset indent
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if (p == NULL)
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newp = malloc(newsize);
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else
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newp = realloc(p, newsize);
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.Ed
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.Pp
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Use the following:
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.Bd -literal -offset indent
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newp = realloc(p, newsize);
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.Ed
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.Pp
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The
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.Fn recallocarray
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function should be used for resizing objects containing sensitive data like
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keys.
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To avoid leaking information,
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it guarantees memory is cleared before placing it on the internal free list.
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Deallocation of such an object should be done by calling
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.Fn freezero .
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.Sh SEE ALSO
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.Xr malloc 3 ,
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.Xr calloc 3 ,
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.Xr alloca 3
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.Sh HISTORY
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The
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.Fn reallocarray
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function appeared in
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.Ox 5.6 ,
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and glibc 2.26.
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The
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.Fn recallocarray
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function appeared in
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.Ox 6.1 .
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The
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.Fn freezero
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function appeared in
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.Ox 6.2 .
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