2020-03-21 02:47:53

by Bernd Edlinger

Subject: [PATCH v6 14/16] pidfd: Use new infrastructure to fix deadlocks in execve

This changes __pidfd_fget to use the new exec_update_mutex
instead of cred_guard_mutex.

This should be safe, as the credentials do not change
before exec_update_mutex is locked. Therefore whatever
file access is possible with holding the cred_guard_mutex
here is also possbile with the exec_update_mutex.

Signed-off-by: Bernd Edlinger <[email protected]>
---
kernel/pid.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index 0f4ecb5..04821f4 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -584,7 +584,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd)
struct file *file;
int ret;

- ret = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ ret = mutex_lock_killable(&task->signal->exec_update_mutex);
if (ret)
return ERR_PTR(ret);

@@ -593,7 +593,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd)
else
file = ERR_PTR(-EPERM);

- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);

return file ?: ERR_PTR(-EBADF);
}
--
1.9.1

2020-03-25 15:41:44

by Christian Brauner

Subject: Re: [PATCH v6 14/16] pidfd: Use new infrastructure to fix deadlocks in execve

On Sat, Mar 21, 2020 at 02:46:16AM +0000, Bernd Edlinger wrote:
> This changes __pidfd_fget to use the new exec_update_mutex
> instead of cred_guard_mutex.
>
> This should be safe, as the credentials do not change
> before exec_update_mutex is locked. Therefore whatever
> file access is possible with holding the cred_guard_mutex
> here is also possbile with the exec_update_mutex.
>
> Signed-off-by: Bernd Edlinger <[email protected]>

Reviewed-by: Christian Brauner <[email protected]>