From: Christoph Hellwig <hch@lst.de>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>,
Luis Chamberlain <mcgrof@kernel.org>,
linux-arm-kernel@lists.infradead.org, x86@kernel.org,
linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
sparclinux@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 6/6] kernel: add a kernel_wait helper
Date: Mon, 15 Jun 2020 15:00:32 +0200 [thread overview]
Message-ID: <20200615130032.931285-7-hch@lst.de> (raw)
In-Reply-To: <20200615130032.931285-1-hch@lst.de>
Add a helper that waits for a pid and stores the status in the passed
in kernel pointer. Use it to fix the usage of kernel_wait4 in
call_usermodehelper_exec_sync that only happens to work due to the
implicit set_fs(KERNEL_DS) for kernel threads.
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
include/linux/sched/task.h | 1 +
kernel/exit.c | 16 ++++++++++++++++
kernel/umh.c | 29 ++++-------------------------
3 files changed, 21 insertions(+), 25 deletions(-)
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 38359071236ad7..a80007df396e95 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -102,6 +102,7 @@ struct task_struct *fork_idle(int);
struct mm_struct *copy_init_mm(void);
extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);
+int kernel_wait(pid_t pid, int *stat);
extern void free_task(struct task_struct *tsk);
diff --git a/kernel/exit.c b/kernel/exit.c
index 727150f2810338..fd598846df0b17 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1626,6 +1626,22 @@ long kernel_wait4(pid_t upid, int __user *stat_addr, int options,
return ret;
}
+int kernel_wait(pid_t pid, int *stat)
+{
+ struct wait_opts wo = {
+ .wo_type = PIDTYPE_PID,
+ .wo_pid = find_get_pid(pid),
+ .wo_flags = WEXITED,
+ };
+ int ret;
+
+ ret = do_wait(&wo);
+ if (ret > 0 && wo.wo_stat)
+ *stat = wo.wo_stat;
+ put_pid(wo.wo_pid);
+ return ret;
+}
+
SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
int, options, struct rusage __user *, ru)
{
diff --git a/kernel/umh.c b/kernel/umh.c
index 1284823dbad338..6fd948e478bec4 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -126,37 +126,16 @@ static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
{
pid_t pid;
- /* If SIGCLD is ignored kernel_wait4 won't populate the status. */
+ /* If SIGCLD is ignored do_wait won't populate the status. */
kernel_sigaction(SIGCHLD, SIG_DFL);
pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
- if (pid < 0) {
+ if (pid < 0)
sub_info->retval = pid;
- } else {
- int ret = -ECHILD;
- /*
- * Normally it is bogus to call wait4() from in-kernel because
- * wait4() wants to write the exit code to a userspace address.
- * But call_usermodehelper_exec_sync() always runs as kernel
- * thread (workqueue) and put_user() to a kernel address works
- * OK for kernel threads, due to their having an mm_segment_t
- * which spans the entire address space.
- *
- * Thus the __user pointer cast is valid here.
- */
- kernel_wait4(pid, (int __user *)&ret, 0, NULL);
-
- /*
- * If ret is 0, either call_usermodehelper_exec_async failed and
- * the real error code is already in sub_info->retval or
- * sub_info->retval is 0 anyway, so don't mess with it then.
- */
- if (ret)
- sub_info->retval = ret;
- }
+ else
+ kernel_wait(pid, &sub_info->retval);
/* Restore default kernel sig handler */
kernel_sigaction(SIGCHLD, SIG_IGN);
-
umh_complete(sub_info);
}
--
2.26.2
next prev parent reply other threads:[~2020-06-15 13:01 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-15 13:00 properly support exec and wait with kernel pointers Christoph Hellwig
2020-06-15 13:00 ` [PATCH 1/6] exec: cleanup the execve wrappers Christoph Hellwig
2020-06-15 13:00 ` [PATCH 2/6] exec: simplify the compat syscall handling Christoph Hellwig
2020-06-15 13:31 ` Arnd Bergmann
2020-06-15 14:12 ` Christoph Hellwig
2020-06-15 14:40 ` Arnd Bergmann
2020-06-15 14:43 ` Christoph Hellwig
2020-06-15 14:46 ` Arnd Bergmann
2020-06-15 15:09 ` Christoph Hellwig
2020-06-15 15:33 ` Brian Gerst
2020-06-15 16:41 ` Christoph Hellwig
2020-06-15 14:48 ` Brian Gerst
2020-06-15 18:47 ` Arnd Bergmann
2020-06-15 19:45 ` Brian Gerst
2020-06-15 13:00 ` [PATCH 3/6] exec: cleanup the count() function Christoph Hellwig
2020-06-15 13:00 ` [PATCH 4/6] exec: split prepare_arg_pages Christoph Hellwig
2020-06-15 13:00 ` [PATCH 5/6] exec: add a kernel_execveat helper Christoph Hellwig
2020-06-15 13:00 ` Christoph Hellwig [this message]
2020-06-15 13:42 ` properly support exec and wait with kernel pointers Arnd Bergmann
2020-06-18 14:46 properly support exec and wait with kernel pointers v2 Christoph Hellwig
2020-06-18 14:46 ` [PATCH 6/6] kernel: add a kernel_wait helper Christoph Hellwig
2020-06-19 21:17 ` Luis Chamberlain
2020-06-20 6:35 ` Christoph Hellwig
2020-06-20 17:02 ` Luis Chamberlain
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