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    SubjectRe: [PATCH 1/9] exec_path 1/9: introduce ->exec_path and switch /proc/*/exe
    On Thu, Jun 04, 2009 at 03:04:22AM +0400, Alexey Dobriyan wrote:
    > diff --git a/fs/binfmt_som.c b/fs/binfmt_som.c
    > index eff74b9..6c56262 100644
    > --- a/fs/binfmt_som.c
    > +++ b/fs/binfmt_som.c
    > @@ -174,6 +174,7 @@ static int map_som_binary(struct file *file,
    > up_write(&current->mm->mmap_sem);
    > if (retval > 0 || retval < -1024)
    > retval = 0;
    > + set_task_exec_path(current, &bprm->file->f_path);

    Oh? Even on failure exits?
    > + if (!path->mnt || !path->dentry)
    > + return -ENOENT;

    Umm... I really don't like that. Note that path with NULL vfsmount
    and non-NULL dentry should never happen. If anything, we ought
    to add path_empty(path) (!(path)->mnt) and convert such places to it.

    > +static inline void set_task_exec_path(struct task_struct *tsk, struct path *path)
    > +{
    > + struct path old_path;
    > +
    > + path_get(path);
    > + task_lock(tsk);
    > + old_path = tsk->exec_path;
    > + tsk->exec_path = *path;
    > + task_unlock(tsk);
    > + path_put(&old_path);
    > +}

    Do we ever have a right to do that to anything other than current? Note
    that fork() is a special case anyway...

    > + set_task_exec_path(tsk, &(struct path){ .mnt = NULL, .dentry = NULL });

    Ew...

    > + get_task_exec_path(current, &p->exec_path);
    > +

    We already have that value sitting there, so why not get_path(&p->exec_path)?

    The real problem I have with that we *really* can't umount the filesystem
    that used to host the binary anymore. At all.

    Frankly, I'm almost tempted to add explicit way to switch the damn thing
    via /proc/self/something - e.g. allow a binary to write a pathname to
    /proc/self/set_exec and have that switch the sucker. The interesting
    part, of course, is figuring out the security implications of that...


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