From: Oleg Nesterov <oleg@redhat.com>
To: Rob Landley <rob@landley.net>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Linux Embedded <linux-embedded@vger.kernel.org>,
dalias@libc.org,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: execve(NULL, argv, envp) for nommu?
Date: Wed, 13 Sep 2017 16:20:11 +0200 [thread overview]
Message-ID: <20170913142011.GA9563@redhat.com> (raw)
In-Reply-To: <20170912154549.GA31411@redhat.com>
On 09/12, Oleg Nesterov wrote:
>
> On 09/12, Rob Landley wrote:
> >
> > On 09/11/2017 10:15 AM, Oleg Nesterov wrote:
> > > On 09/08, Rob Landley wrote:
> > >>
> > >> So is exec(NULL, argv, envp) a reasonable thing to want?
> > >
> > > I think that something like prctl(PR_OPEN_EXE_FILE) which does
> > >
> > > dentry_open(current->mm->exe_file->path, O_PATH)
> > >
> > > and returns fd make more sense.
> > >
> > > Then you can do execveat(fd, "", ..., AT_EMPTY_PATH).
> > I'm all for it? That sounds like a cosmetic difference, a more verbose
> > way of achieving the same outcome.
>
> Simpler to implement. Something like the (untested) patch below. Not sure
> it is correct, not sure it is good idea, etc.
OTOH... with the trivial patch below
execveat(AT_FDCWD, "", NULL, NULL, AT_EMPTY_PATH);
should always work, even if the binary is not in scope after chroot, or if
it is no longer executable, or unlinked. But I am not sure what else should
we do to avoid the security problems.
Oleg.
--- x/fs/exec.c
+++ x/fs/exec.c
@@ -832,23 +832,32 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags)
{
struct file *file;
int err;
- struct open_flags open_exec_flags = {
- .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
- .acc_mode = MAY_EXEC,
- .intent = LOOKUP_OPEN,
- .lookup_flags = LOOKUP_FOLLOW,
- };
-
- if ((flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
- return ERR_PTR(-EINVAL);
- if (flags & AT_SYMLINK_NOFOLLOW)
- open_exec_flags.lookup_flags &= ~LOOKUP_FOLLOW;
- if (flags & AT_EMPTY_PATH)
- open_exec_flags.lookup_flags |= LOOKUP_EMPTY;
- file = do_filp_open(fd, name, &open_exec_flags);
- if (IS_ERR(file))
- goto out;
+ if (fd == AT_FDCWD && name->name[0] == '\0' && flags == AT_EMPTY_PATH) {
+ file = get_mm_exe_file(current->mm);
+ if (!file) {
+ file = ERR_PTR(-ENOENT);
+ goto out;
+ }
+ } else {
+ struct open_flags open_exec_flags = {
+ .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
+ .acc_mode = MAY_EXEC,
+ .intent = LOOKUP_OPEN,
+ .lookup_flags = LOOKUP_FOLLOW,
+ };
+
+ if ((flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
+ return ERR_PTR(-EINVAL);
+ if (flags & AT_SYMLINK_NOFOLLOW)
+ open_exec_flags.lookup_flags &= ~LOOKUP_FOLLOW;
+ if (flags & AT_EMPTY_PATH)
+ open_exec_flags.lookup_flags |= LOOKUP_EMPTY;
+
+ file = do_filp_open(fd, name, &open_exec_flags);
+ if (IS_ERR(file))
+ goto out;
+ }
err = -EACCES;
if (!S_ISREG(file_inode(file)->i_mode))
next prev parent reply other threads:[~2017-09-13 14:20 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-05 7:34 execve(NULL, argv, envp) for nommu? Rob Landley
2017-09-05 9:00 ` Geert Uytterhoeven
2017-09-05 13:24 ` Alan Cox
2017-09-06 1:12 ` Rob Landley
2017-09-08 21:18 ` Rob Landley
2017-09-11 15:15 ` Oleg Nesterov
2017-09-12 10:48 ` Rob Landley
2017-09-12 11:30 ` Geert Uytterhoeven
2017-09-12 13:45 ` Rob Landley
2017-09-13 19:33 ` Alan Cox
2017-09-12 15:45 ` Oleg Nesterov
2017-09-13 14:20 ` Oleg Nesterov [this message]
2017-09-11 18:14 ` Alan Cox
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