From: Rich Felker <dalias@xxxxxxxx> On NOMMU archs, the FDPIC ELF loader sets up the usable brk range to overlap with all but the last PAGE_SIZE bytes of the stack. This leads to catastrophic memory reuse/corruption if brk is used. Fix by setting the brk area to zero size to disable its use. Signed-off-by: Rich Felker <dalias@xxxxxxxx> --- There is no reason for the kernel to be providing a brk area at all on NOMMU; the bFLT loader does not provide one, uClibc never uses brk on NOMMU targets, and musl libc goes out of its way to avoid using brk that might run into the stack. --- fs/binfmt_elf_fdpic.c.orig 2015-08-20 18:05:19.089888654 +0000 +++ fs/binfmt_elf_fdpic.c 2015-08-20 18:10:01.519871432 +0000 @@ -374,10 +388,7 @@ static int load_elf_fdpic_binary(struct PAGE_ALIGN(current->mm->start_brk); #else - /* create a stack and brk area big enough for everyone - * - the brk heap starts at the bottom and works up - * - the stack starts at the top and works down - */ + /* create a stack area and zero-size brk area */ stack_size = (stack_size + PAGE_SIZE - 1) & PAGE_MASK; if (stack_size < PAGE_SIZE * 2) stack_size = PAGE_SIZE * 2; @@ -400,8 +411,6 @@ static int load_elf_fdpic_binary(struct current->mm->brk = current->mm->start_brk; current->mm->context.end_brk = current->mm->start_brk; - current->mm->context.end_brk += - (stack_size > PAGE_SIZE) ? (stack_size - PAGE_SIZE) : 0; current->mm->start_stack = current->mm->start_brk + stack_size; #endif -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
