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Date: Thu, 22 Jun 2017 10:38:38 -0700
From: Kees Cook <keescook@...omium.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Rik van Riel <riel@...hat.com>, Daniel Micay <danielmicay@...il.com>,
Qualys Security Advisory <qsa@...lys.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
x86@...nel.org, Alexander Viro <viro@...iv.linux.org.uk>,
Dmitry Safonov <dsafonov@...tuozzo.com>,
Andy Lutomirski <luto@...capital.net>,
Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: [PATCH] binfmt_elf: Safely increment argv pointers
When building the argv/envp pointers, the envp is needlessly
pre-incremented instead of just continuing after the argv pointers are
finished. In some (likely impossible) race where the strings could
be changed from userspace between copy_strings() and here, it might
be possible to confuse the envp position. Instead, just use sp like
everything else.
Signed-off-by: Kees Cook <keescook@...omium.org>
---
fs/binfmt_elf.c | 20 +++++++++-----------
1 file changed, 9 insertions(+), 11 deletions(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 7465c3ea5dd5..879ff9c7ffd0 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -163,8 +163,6 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
unsigned long p = bprm->p;
int argc = bprm->argc;
int envc = bprm->envc;
- elf_addr_t __user *argv;
- elf_addr_t __user *envp;
elf_addr_t __user *sp;
elf_addr_t __user *u_platform;
elf_addr_t __user *u_base_platform;
@@ -304,38 +302,38 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
/* Now, let's put argc (and argv, envp if appropriate) on the stack */
if (__put_user(argc, sp++))
return -EFAULT;
- argv = sp;
- envp = argv + argc + 1;
- /* Populate argv and envp */
+ /* Populate list of argv pointers back to argv strings. */
p = current->mm->arg_end = current->mm->arg_start;
while (argc-- > 0) {
size_t len;
- if (__put_user((elf_addr_t)p, argv++))
+ if (__put_user((elf_addr_t)p, sp++))
return -EFAULT;
len = strnlen_user((void __user *)p, MAX_ARG_STRLEN);
if (!len || len > MAX_ARG_STRLEN)
return -EINVAL;
p += len;
}
- if (__put_user(0, argv))
+ if (__put_user(0, sp++))
return -EFAULT;
- current->mm->arg_end = current->mm->env_start = p;
+ current->mm->arg_end = p;
+
+ /* Populate list of envp pointers back to envp strings. */
+ current->mm->env_end = current->mm->env_start = p;
while (envc-- > 0) {
size_t len;
- if (__put_user((elf_addr_t)p, envp++))
+ if (__put_user((elf_addr_t)p, sp++))
return -EFAULT;
len = strnlen_user((void __user *)p, MAX_ARG_STRLEN);
if (!len || len > MAX_ARG_STRLEN)
return -EINVAL;
p += len;
}
- if (__put_user(0, envp))
+ if (__put_user(0, sp++))
return -EFAULT;
current->mm->env_end = p;
/* Put the elf_info on the stack in the right place. */
- sp = (elf_addr_t __user *)envp + 1;
if (copy_to_user(sp, elf_info, ei_index * sizeof(elf_addr_t)))
return -EFAULT;
return 0;
--
2.7.4
--
Kees Cook
Pixel Security
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