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    SubjectRe: [PATCH 1/2] exec: Properly mark the point of no return
    Date
    On 3/5/20 10:15 PM, Eric W. Biederman wrote:
    >
    > Add a flag binfmt->unrecoverable to mark when execution has gotten to
    > the point where it is impossible to return to userspace with the
    > calling process unchanged.
    >
    > While techinically this state starts as soon as de_thread starts
    > killing threads, the only return path at that point is if there is a
    > fatal signal pending. I have choosen instead to set unrecoverable
    > when the killing stops, and there are possibilities of failures other
    > than fatal signals. In particular it is possible for the allocation
    > of a new sighand structure to fail.
    >
    > Setting unrecoverable at this point has the benefit that other actions
    > can be taken after the other threads are all dead, and the
    > unrecoverable flag can double as a flag that those actions have been
    > taken.
    >
    > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    > ---
    > fs/exec.c | 7 ++++---
    > include/linux/binfmts.h | 7 ++++++-
    > 2 files changed, 10 insertions(+), 4 deletions(-)
    >
    > diff --git a/fs/exec.c b/fs/exec.c
    > index db17be51b112..c243f9660d46 100644
    > --- a/fs/exec.c
    > +++ b/fs/exec.c
    > @@ -1061,7 +1061,7 @@ static int exec_mmap(struct mm_struct *mm)
    > * disturbing other processes. (Other processes might share the signal
    > * table via the CLONE_SIGHAND option to clone().)
    > */
    > -static int de_thread(struct task_struct *tsk)
    > +static int de_thread(struct linux_binprm *bprm, struct task_struct *tsk)
    > {
    > struct signal_struct *sig = tsk->signal;
    > struct sighand_struct *oldsighand = tsk->sighand;
    > @@ -1182,6 +1182,7 @@ static int de_thread(struct task_struct *tsk)
    > release_task(leader);
    > }
    >
    > + bprm->unrecoverable = true;
    > sig->group_exit_task = NULL;
    > sig->notify_count = 0;
    >
    > @@ -1266,7 +1267,7 @@ int flush_old_exec(struct linux_binprm * bprm)
    > * Make sure we have a private signal table and that
    > * we are unassociated from the previous thread group.
    > */
    > - retval = de_thread(current);
    > + retval = de_thread(bprm, current);

    can we get rid of passing current as parameter here?

    Thanks
    Bernd.

    > if (retval)
    > goto out;
    >
    > @@ -1664,7 +1665,7 @@ int search_binary_handler(struct linux_binprm *bprm)
    >
    > read_lock(&binfmt_lock);
    > put_binfmt(fmt);
    > - if (retval < 0 && !bprm->mm) {
    > + if (retval < 0 && bprm->unrecoverable) {
    > /* we got to flush_old_exec() and failed after it */
    > read_unlock(&binfmt_lock);
    > force_sigsegv(SIGSEGV);
    > diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
    > index b40fc633f3be..12263115ce7a 100644
    > --- a/include/linux/binfmts.h
    > +++ b/include/linux/binfmts.h
    > @@ -44,7 +44,12 @@ struct linux_binprm {
    > * exec has happened. Used to sanitize execution environment
    > * and to set AT_SECURE auxv for glibc.
    > */
    > - secureexec:1;
    > + secureexec:1,
    > + /*
    > + * Set when changes have been made that prevent returning
    > + * to userspace.
    > + */
    > + unrecoverable:1;
    > #ifdef __alpha__
    > unsigned int taso:1;
    > #endif
    >

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