path: root/manual/memory.texi
diff options
authorDennis Wölfing <denniswoelfing@gmx.de>2017-05-30 18:26:19 -0300
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2017-05-30 18:27:57 -0300
commit2e0bbbfbf95fc9e22692e93658a6fbdd2d4554da (patch)
tree662856c19816b2b441dbfda3e15ca771eb303e5f /manual/memory.texi
parent4f26ef1b67287d1f2c32865f7d79c13abda81915 (diff)
Add reallocarray function
The reallocarray function is an extension from OpenBSD. It is an integer-overflow-safe replacement for realloc(p, X*Y) and malloc(X*Y) (realloc(NULL, X*Y)). It can therefore help in preventing certain security issues in code. This is an updated version of a patch originally submitted by Rüdiger Sonderfeld in May 2014 [1]. Checked on i686-linux-gnu and x86_64-linux-gnu. [1] <https://sourceware.org/ml/libc-alpha/2014-05/msg00481.html>. 2017-05-30 Dennis Wölfing <denniswoelfing@gmx.de> Rüdiger Sonderfeld <ruediger@c-plusplus.de> * include/stdlib.h (__libc_reallocarray): New declaration. * malloc/Makefile (routines): Add reallocarray. (tests): Add tst-reallocarray.c. * malloc/Versions: Add reallocarray and __libc_reallocarray. * malloc/malloc-internal.h (check_mul_overflow_size_t): New inline function. * malloc/malloc.h (reallocarray): New declaration. * stdlib/stdlib.h (reallocarray): Likewise. * malloc/reallocarray.c: New file. * malloc/tst-reallocarray.c: New test file. * manual/memory.texi: Document reallocarray. * sysdeps/unix/sysv/linux/aarch64/libc.abilist: Add reallocarray. * sysdeps/unix/sysv/linux/alpha/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/arm/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/hppa/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/i386/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/ia64/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/microblaze/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/nios2/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/sh/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/tilepro/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/x86_64/64/libc.abilist: Likewise. * sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist: Likewise.
Diffstat (limited to 'manual/memory.texi')
1 files changed, 36 insertions, 10 deletions
diff --git a/manual/memory.texi b/manual/memory.texi
index a256ca07b2b..fb6b594ef19 100644
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -751,8 +751,8 @@ be a buffer that you use to hold a line being read from a file; no matter
how long you make the buffer initially, you may encounter a line that is
-You can make the block longer by calling @code{realloc}. This function
-is declared in @file{stdlib.h}.
+You can make the block longer by calling @code{realloc} or
+@code{reallocarray}. These functions are declared in @file{stdlib.h}.
@pindex stdlib.h
@comment malloc.h stdlib.h
@@ -816,9 +816,29 @@ behavior, and will probably crash when @code{realloc} is passed a null
@end deftypefun
-Like @code{malloc}, @code{realloc} may return a null pointer if no
-memory space is available to make the block bigger. When this happens,
-the original block is untouched; it has not been modified or relocated.
+@comment malloc.h stdlib.h
+@comment BSD
+@deftypefun {void *} reallocarray (void *@var{ptr}, size_t @var{nmemb}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
+The @code{reallocarray} function changes the size of the block whose address
+is @var{ptr} to be long enough to contain a vector of @var{nmemb} elements,
+each of size @var{size}. It is equivalent to @samp{realloc (@var{ptr},
+@var{nmemb} * @var{size})}, except that @code{reallocarray} fails safely if
+the multiplication overflows, by setting @code{errno} to @code{ENOMEM},
+returning a null pointer, and leaving the original block unchanged.
+@code{reallocarray} should be used instead of @code{realloc} when the new size
+of the allocated block is the result of a multiplication that might overflow.
+@strong{Portability Note:} This function is not part of any standard. It was
+first introduced in OpenBSD 5.6.
+@end deftypefun
+Like @code{malloc}, @code{realloc} and @code{reallocarray} may return a null
+pointer if no memory space is available to make the block bigger. When this
+happens, the original block is untouched; it has not been modified or
In most cases it makes no difference what happens to the original block
when @code{realloc} fails, because the application program cannot continue
@@ -838,16 +858,17 @@ xrealloc (void *ptr, size_t size)
@end smallexample
-You can also use @code{realloc} to make a block smaller. The reason you
-would do this is to avoid tying up a lot of memory space when only a little
-is needed.
+You can also use @code{realloc} or @code{reallocarray} to make a block
+smaller. The reason you would do this is to avoid tying up a lot of memory
+space when only a little is needed.
@comment The following is no longer true with the new malloc.
@comment But it seems wise to keep the warning for other implementations.
In several allocation implementations, making a block smaller sometimes
necessitates copying it, so it can fail if no other space is available.
-If the new size you specify is the same as the old size, @code{realloc}
-is guaranteed to change nothing and return the same address that you gave.
+If the new size you specify is the same as the old size, @code{realloc} and
+@code{reallocarray} are guaranteed to change nothing and return the same
+address that you gave.
@node Allocating Cleared Space
@subsubsection Allocating Cleared Space
@@ -1588,6 +1609,11 @@ Malloc}.
Make a block previously allocated by @code{malloc} larger or smaller,
possibly by copying it to a new location. @xref{Changing Block Size}.
+@item void *reallocarray (void *@var{ptr}, size_t @var{nmemb}, size_t @var{size})
+Change the size of a block previously allocated by @code{malloc} to
+@code{@var{nmemb} * @var{size}} bytes as with @code{realloc}. @xref{Changing
+Block Size}.
@item void *calloc (size_t @var{count}, size_t @var{eltsize})
Allocate a block of @var{count} * @var{eltsize} bytes using
@code{malloc}, and set its contents to zero. @xref{Allocating Cleared