Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261518AbVCRJIO (ORCPT ); Fri, 18 Mar 2005 04:08:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261523AbVCRJHE (ORCPT ); Fri, 18 Mar 2005 04:07:04 -0500 Received: from fire.osdl.org ([65.172.181.4]:50834 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S261518AbVCRJFs (ORCPT ); Fri, 18 Mar 2005 04:05:48 -0500 Date: Fri, 18 Mar 2005 01:05:01 -0800 From: Andrew Morton To: Herbert Xu Cc: yxie@cs.stanford.edu, linux-kernel@vger.kernel.org Subject: Re: Potential DOS in load_elf_library? Message-Id: <20050318010501.3190d8c6.akpm@osdl.org> In-Reply-To: References: X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3399 Lines: 102 Herbert Xu wrote: > > Yichen Xie wrote: > > Hi guys, I was looking at the load_elf_library function (fs/binfmt_elf.c) > > in 2.6.10, and noticed the following: > > > > elf_phdata = (struct elf_phdr *) kmalloc(j, GFP_KERNEL); > > ... > > while (elf_phdata->p_type != PT_LOAD) elf_phdata++; > > ... > > kfree(elf_phdata); > > > > Could this be problematic since the pointer being freed might be different > > from that returned from kmalloc? > > Indeed. This bug has been around since last century. Duh, I was looking at the wrong function. Thanks. > How does this look? I think it'd be better to use epptr everywhere, so we can see that it only gets assigned, tested then freed. --- 25/fs/binfmt_elf.c~load_elf_binary-kfree-fix 2005-03-18 01:00:49.000000000 -0800 +++ 25-akpm/fs/binfmt_elf.c 2005-03-18 01:03:14.000000000 -0800 @@ -1028,6 +1028,7 @@ out_free_ph: static int load_elf_library(struct file *file) { struct elf_phdr *elf_phdata; + struct elf_phdr *eppnt; unsigned long elf_bss, bss, len; int retval, error, i, j; struct elfhdr elf_ex; @@ -1051,44 +1052,47 @@ static int load_elf_library(struct file /* j < ELF_MIN_ALIGN because elf_ex.e_phnum <= 2 */ error = -ENOMEM; - elf_phdata = (struct elf_phdr *) kmalloc(j, GFP_KERNEL); + elf_phdata = kmalloc(j, GFP_KERNEL); if (!elf_phdata) goto out; + eppnt = elf_phdata; error = -ENOEXEC; - retval = kernel_read(file, elf_ex.e_phoff, (char *) elf_phdata, j); + retval = kernel_read(file, elf_ex.e_phoff, (char *)eppnt, j); if (retval != j) goto out_free_ph; for (j = 0, i = 0; ip_type == PT_LOAD) j++; + if ((eppnt + i)->p_type == PT_LOAD) + j++; if (j != 1) goto out_free_ph; - while (elf_phdata->p_type != PT_LOAD) elf_phdata++; + while (eppnt->p_type != PT_LOAD) + eppnt++; /* Now use mmap to map the library into memory. */ down_write(¤t->mm->mmap_sem); error = do_mmap(file, - ELF_PAGESTART(elf_phdata->p_vaddr), - (elf_phdata->p_filesz + - ELF_PAGEOFFSET(elf_phdata->p_vaddr)), + ELF_PAGESTART(eppnt->p_vaddr), + (eppnt->p_filesz + + ELF_PAGEOFFSET(eppnt->p_vaddr)), PROT_READ | PROT_WRITE | PROT_EXEC, MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE, - (elf_phdata->p_offset - - ELF_PAGEOFFSET(elf_phdata->p_vaddr))); + (eppnt->p_offset - + ELF_PAGEOFFSET(eppnt->p_vaddr))); up_write(¤t->mm->mmap_sem); - if (error != ELF_PAGESTART(elf_phdata->p_vaddr)) + if (error != ELF_PAGESTART(eppnt->p_vaddr)) goto out_free_ph; - elf_bss = elf_phdata->p_vaddr + elf_phdata->p_filesz; + elf_bss = eppnt->p_vaddr + eppnt->p_filesz; if (padzero(elf_bss)) { error = -EFAULT; goto out_free_ph; } - len = ELF_PAGESTART(elf_phdata->p_filesz + elf_phdata->p_vaddr + ELF_MIN_ALIGN - 1); - bss = elf_phdata->p_memsz + elf_phdata->p_vaddr; + len = ELF_PAGESTART(eppnt->p_filesz + eppnt->p_vaddr + ELF_MIN_ALIGN - 1); + bss = eppnt->p_memsz + eppnt->p_vaddr; if (bss > len) { down_write(¤t->mm->mmap_sem); do_brk(len, bss - len); _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/