autofs4: check kernel communication pipe is valid for write

It is possible for an autofs mount to become catatonic (and for the daemon
communication pipe to become NULL) after a wait has been initiallized but
before the request has been sent to the daemon.  We need to check for this
before sending the request packet.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 2 deletions

diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index 1132cc2a0310..dd2914d7ad7f 100644
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -99,6 +99,7 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
                 union autofs_packet_union v4_pkt;
                 union autofs_v5_packet_union v5_pkt;
         } pkt;
+        struct file *pipe = NULL;
         size_t pktsz;
 
         DPRINTK("wait id = 0x%08lx, name = %.*s, type=%d",
@@ -164,8 +165,19 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
                 return;
         }
 
-        if (autofs4_write(sbi->pipe, &pkt, pktsz))
-                autofs4_catatonic_mode(sbi);
+        /* Check if we have become catatonic */
+        mutex_lock(&sbi->wq_mutex);
+        if (!sbi->catatonic) {
+                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);
+        }
 }
 
 static int autofs4_getpath(struct autofs_sb_info *sbi,