From 3cd6f5229f079f892411e82fce3fe15c78eef4d8 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Thu, 27 Jun 2013 12:48:59 -0400 Subject: [PATCH] disallow creation of objects larger than PTRDIFF_MAX via mmap internally, other parts of the library assume sizes don't overflow ssize_t and/or ptrdiff_t, and the way this assumption is made valid is by preventing creating of such large objects. malloc already does so, but the check was missing from mmap. this is also a quality of implementation issue: even if the implementation internally could handle such objects, applications could inadvertently invoke undefined behavior by subtracting pointers within an object. it is very difficult to guard against this in applications, so a good implementation should simply ensure that it does not happen. --- src/mman/mmap.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/src/mman/mmap.c b/src/mman/mmap.c index e99271f7..b56cff86 100644 --- a/src/mman/mmap.c +++ b/src/mman/mmap.c @@ -1,6 +1,7 @@ #include #include #include +#include #include #include "syscall.h" #include "libc.h" @@ -20,6 +21,10 @@ void *__mmap(void *start, size_t len, int prot, int flags, int fd, off_t off) errno = EINVAL; return MAP_FAILED; } + if (len >= PTRDIFF_MAX) { + errno = ENOMEM; + return MAP_FAILED; + } if (flags & MAP_FIXED) __vm_lock(-1); #ifdef SYS_mmap2 ret = (void *)syscall(SYS_mmap2, start, len, prot, flags, fd, off>>12); -- 2.25.1