[PATCH 3.2 50/79] autofs4: catatonic_mode vs. notify_daemon race

[Ben Hutchings]

3.2.99-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

commit 8753333266be67ff3a984ac1f6566d31c260bee4 upstream.

we need to hold ->wq_mutex while we are forming the packet to send,
lest we have autofs4_catatonic_mode() setting wq->name.name to NULL
just as autofs4_notify_daemon() decides to memcpy() from it...

We do have check for catatonic mode immediately after that (under
->wq_mutex, as it ought to be) and packet won't be actually sent,
but it'll be too late for us if we oops on that memcpy() from NULL...

Fix is obvious - just extend the area covered by ->wq_mutex over
that switch and check whether it's catatonic *before* doing anything
else.

Acked-by: Ian Kent <raven@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/autofs4/waitq.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -110,6 +110,13 @@ static void autofs4_notify_daemon(struct
 
 	pkt.hdr.proto_version = sbi->version;
 	pkt.hdr.type = type;
+	mutex_lock(&sbi->wq_mutex);
+
+	/* Check if we have become catatonic */
+	if (sbi->catatonic) {
+		mutex_unlock(&sbi->wq_mutex);
+		return;
+	}
 	switch (type) {
 	/* Kernel protocol v4 missing and expire packets */
 	case autofs_ptype_missing:
@@ -163,22 +170,18 @@ static void autofs4_notify_daemon(struct
 	}
 	default:
 		printk("autofs4_notify_daemon: bad type %d!\n", type);
+		mutex_unlock(&sbi->wq_mutex);
 		return;
 	}
 
-	/* Check if we have become catatonic */
-	mutex_lock(&sbi->wq_mutex);
-	if (!sbi->catatonic) {
-		pipe = sbi->pipe;
-		get_file(pipe);
-	}
+	pipe = sbi->pipe;
+	get_file(pipe);
+
 	mutex_unlock(&sbi->wq_mutex);
 
-	if (pipe) {
-		if (autofs4_write(pipe, &pkt, pktsz))
-			autofs4_catatonic_mode(sbi);
-		fput(pipe);
-	}
+	if (autofs4_write(pipe, &pkt, pktsz))
+		autofs4_catatonic_mode(sbi);
+	fput(pipe);
 }
 
 static int autofs4_getpath(struct autofs_sb_info *sbi,