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SubjectRe: [PATCH 1/3] exec: introduce exec_binprm() for "depth == 0" code
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On Thu, Aug 1, 2013 at 12:05 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> task_pid_nr_ns() and trace/ptrace code in the middle of the
> recursive search_binary_handler() looks confusing and imho
> annoying. We only need this code if "depth == 0", lets add
> a simple helper which calls search_binary_handler() and does
> trace_sched_process_exec() + ptrace_event().
>
> The patch also moves the setting of task->did_exec, we need
> to do this only once.
>
> Note: we can kill either task->did_exec or PF_FORKNOEXEC.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> fs/exec.c | 36 ++++++++++++++++++++++--------------
> 1 files changed, 22 insertions(+), 14 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 9c73def..a9ae4f2 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1373,7 +1373,6 @@ int search_binary_handler(struct linux_binprm *bprm)
> unsigned int depth = bprm->recursion_depth;
> int try,retval;
> struct linux_binfmt *fmt;
> - pid_t old_pid, old_vpid;
>
> /* This allows 4 levels of binfmt rewrites before failing hard. */
> if (depth > 5)
> @@ -1387,12 +1386,6 @@ int search_binary_handler(struct linux_binprm *bprm)
> if (retval)
> return retval;
>
> - /* Need to fetch pid before load_binary changes it */
> - old_pid = current->pid;
> - rcu_read_lock();
> - old_vpid = task_pid_nr_ns(current, task_active_pid_ns(current->parent));
> - rcu_read_unlock();
> -
> retval = -ENOENT;
> for (try=0; try<2; try++) {
> read_lock(&binfmt_lock);
> @@ -1407,16 +1400,11 @@ int search_binary_handler(struct linux_binprm *bprm)
> retval = fn(bprm);
> bprm->recursion_depth = depth;
> if (retval >= 0) {
> - if (depth == 0) {
> - trace_sched_process_exec(current, old_pid, bprm);
> - ptrace_event(PTRACE_EVENT_EXEC, old_vpid);
> - }
> put_binfmt(fmt);
> allow_write_access(bprm->file);
> if (bprm->file)
> fput(bprm->file);
> bprm->file = NULL;
> - current->did_exec = 1;
> proc_exec_connector(current);
> return retval;
> }
> @@ -1450,9 +1438,29 @@ int search_binary_handler(struct linux_binprm *bprm)
> }
> return retval;
> }
> -
> EXPORT_SYMBOL(search_binary_handler);
>
> +static int exec_binprm(struct linux_binprm *bprm)
> +{
> + pid_t old_pid, old_vpid;
> + int ret;
> +
> + /* Need to fetch pid before load_binary changes it */
> + old_pid = current->pid;
> + rcu_read_lock();
> + old_vpid = task_pid_nr_ns(current, task_active_pid_ns(current->parent));
> + rcu_read_unlock();
> +
> + ret = search_binary_handler(bprm);
> + if (ret >= 0) {
> + trace_sched_process_exec(current, old_pid, bprm);
> + ptrace_event(PTRACE_EVENT_EXEC, old_vpid);
> + current->did_exec = 1;
> + }

Cleanup looks good. One idea here, though: this could be made more
pretty by doing:

if (ret < 0)
return ret;

to avoid the indentation for the "expected" code path.

-Kees

> +
> + return ret;
> +}
> +
> /*
> * sys_execve() executes a new program.
> */
> @@ -1541,7 +1549,7 @@ static int do_execve_common(const char *filename,
> if (retval < 0)
> goto out;
>
> - retval = search_binary_handler(bprm);
> + retval = exec_binprm(bprm);
> if (retval < 0)
> goto out;
>
> --
> 1.5.5.1
>



--
Kees Cook
Chrome OS Security


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