autofs4: catatonic_mode vs. notify_daemon race

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@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 14 insertions, 11 deletions

diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index c13273afd546..9a0256da5d56 100644
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -110,6 +110,13 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
 
         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 autofs_sb_info *sbi,
         }
         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,