2007-05-28 13:33:23

by Alexey Dobriyan

Subject: [PATCH] /proc/*/environ: wrong placing of ptrace_may_attach() check

Signed-off-by: Alexey Dobriyan <[email protected]>
---

fs/proc/base.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -204,12 +204,17 @@ static int proc_pid_environ(struct task_
int res = 0;
struct mm_struct *mm = get_task_mm(task);
if (mm) {
- unsigned int len = mm->env_end - mm->env_start;
+ unsigned int len;
+
+ res = -ESRCH;
+ if (!ptrace_may_attach(task))
+ goto out;
+
+ len = mm->env_end - mm->env_start;
if (len > PAGE_SIZE)
len = PAGE_SIZE;
res = access_process_vm(task, mm->env_start, buffer, len, 0);
- if (!ptrace_may_attach(task))
- res = -ESRCH;
+out:
mmput(mm);
}
return res;

2007-05-30 00:17:18

by Andrew Morton

Subject: Re: [PATCH] /proc/*/environ: wrong placing of ptrace_may_attach() check

On Mon, 28 May 2007 17:41:57 +0400
Alexey Dobriyan <[email protected]> wrote:

> Signed-off-by: Alexey Dobriyan <[email protected]>

Better changelogs, please.

> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -204,12 +204,17 @@ static int proc_pid_environ(struct task_
> int res = 0;
> struct mm_struct *mm = get_task_mm(task);
> if (mm) {
> - unsigned int len = mm->env_end - mm->env_start;
> + unsigned int len;
> +
> + res = -ESRCH;
> + if (!ptrace_may_attach(task))
> + goto out;
> +
> + len = mm->env_end - mm->env_start;
> if (len > PAGE_SIZE)
> len = PAGE_SIZE;
> res = access_process_vm(task, mm->env_start, buffer, len, 0);
> - if (!ptrace_may_attach(task))
> - res = -ESRCH;
> +out:
> mmput(mm);
> }
> return res;

What's wrong with the existing code? It's a bit dopey-looking and can, I
guess, permit a task to cause a pagefault in an mm which it doesn't have
permission to read from. But is there some more serious problem being
fixed here?

I shouldn't have to ask this stuff.

2007-05-30 08:31:17

by Alexey Dobriyan

Subject: Re: [PATCH] /proc/*/environ: wrong placing of ptrace_may_attach() check

On Tue, May 29, 2007 at 05:16:23PM -0700, Andrew Morton wrote:
> On Mon, 28 May 2007 17:41:57 +0400
> Alexey Dobriyan <[email protected]> wrote:

> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -204,12 +204,17 @@ static int proc_pid_environ(struct task_
> > int res = 0;
> > struct mm_struct *mm = get_task_mm(task);
> > if (mm) {
> > - unsigned int len = mm->env_end - mm->env_start;
> > + unsigned int len;
> > +
> > + res = -ESRCH;
> > + if (!ptrace_may_attach(task))
> > + goto out;
> > +
> > + len = mm->env_end - mm->env_start;
> > if (len > PAGE_SIZE)
> > len = PAGE_SIZE;
> > res = access_process_vm(task, mm->env_start, buffer, len, 0);
> > - if (!ptrace_may_attach(task))
> > - res = -ESRCH;
> > +out:
> > mmput(mm);
> > }
> > return res;
>
> What's wrong with the existing code? It's a bit dopey-looking and can, I
> guess, permit a task to cause a pagefault in an mm which it doesn't have
> permission to read from. But is there some more serious problem being
> fixed here?

I think not, because environment will be copied from target task, stay
in kernel tmp buffer, but not copied to target buffer due to -ESRCH.
But such code is asking for problems.