Re: Chroot bug (was: sys_chroot+sys_fchdir Fix)

From: Jan Engelhardt
Date: Tue Sep 25 2007 - 11:20:36 EST

On Sep 26 2007 00:40, David Newall wrote:
> Miloslav Semler pointed out that a root process can chdir("..") out of its
> chroot. Although this is documented in the man page, it conflicts with the
> essential function, which is to change the root directory of the process. In
> addition to any creative uses, for example Philipp Marek's loading dynamic
> libraries, it seems clear that the prime purpose of chroot is to aid security.
> Being able to cd your way out is handy for the bad guys, but the good guys
> don't need it; there are a thousand better, safer solutions.

So what? Just do this: chdir into the root after chroot.

It won't conform to SVR4/4.4BSD anymore, but hey, let Linux set some
sane standard ain't bad either. I doubt anyone really relies on the
fact that after chroot, your cwd might be outside the root.

Signed-off-by: Jan Engelhardt <jengelh@xxxxxx>

fs/open.c | 1 +
1 file changed, 1 insertion(+)

Index: linux-2.6.23/fs/open.c
--- linux-2.6.23.orig/fs/open.c
+++ linux-2.6.23/fs/open.c
@@ -547,6 +547,7 @@ asmlinkage long sys_chroot(const char __

set_fs_root(current->fs, nd.mnt, nd.dentry);
+ set_fs_pwd(current->fs, nd.mnt, nd.dentry);
error = 0;
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