linux-kernel - [PATCH] um: Fix waitpid() usage in helper code

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Date:	Sun,  9 Aug 2015 22:00:28 +0200
From:	Richard Weinberger <richard@....at>
To:	user-mode-linux-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org, thomas@...3r.de,
	Richard Weinberger <richard@....at>
Subject: [PATCH] um: Fix waitpid() usage in helper code

If UML is executing a helper program it is using
waitpid() with the __WCLONE flag to wait for the program
as the helper is executed from a clone()'ed thread.
While using __WCLONE is perfectly fine for clone()'ed
childs it won't detect terminated childs if the helper
has issued an execve().

We have to use __WALL to wait for both clone()'ed and
regular childs to detect the termination before and
after an execve().

Reported-and-tested-by: Thomas Meyer <thomas@...3r.de>
Signed-off-by: Richard Weinberger <richard@....at>
---
 arch/um/os-Linux/helper.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/um/os-Linux/helper.c b/arch/um/os-Linux/helper.c
index e3ee4a5..3f02d42 100644
--- a/arch/um/os-Linux/helper.c
+++ b/arch/um/os-Linux/helper.c
@@ -96,7 +96,7 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv)
 			       "ret = %d\n", -n);
 			ret = n;
 		}
-		CATCH_EINTR(waitpid(pid, NULL, __WCLONE));
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
 	}
 
 out_free2:
@@ -129,7 +129,7 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 		return err;
 	}
 	if (stack_out == NULL) {
-		CATCH_EINTR(pid = waitpid(pid, &status, __WCLONE));
+		CATCH_EINTR(pid = waitpid(pid, &status, __WALL));
 		if (pid < 0) {
 			err = -errno;
 			printk(UM_KERN_ERR "run_helper_thread - wait failed, "
@@ -148,7 +148,7 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 int helper_wait(int pid)
 {
 	int ret, status;
-	int wflags = __WCLONE;
+	int wflags = __WALL;
 
 	CATCH_EINTR(ret = waitpid(pid, &status, wflags));
 	if (ret < 0) {
-- 
1.8.4.5

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