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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Ian Kent" <raven@themaw.net>,
        "Al Viro" <viro@zeniv.linux.org.uk>
Date:   Sun, 11 Feb 2018 04:20:06 +0000
Message-ID: <lsq.1518322806.420999040@decadent.org.uk>
Subject: [PATCH 3.2 49/79] autofs4: autofs4_wait() vs. autofs4_catatonic_mode()
 race
In-Reply-To: <lsq.1518322802.943358572@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

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

From: Al Viro <viro@zeniv.linux.org.uk>

commit 4041bcdc7bef06a2fb29c57394c713a74bd13b08 upstream.

We need to recheck ->catatonic after autofs4_wait() got ->wq_mutex
for good, or we might end up with wq inserted into queue after
autofs4_catatonic_mode() had done its thing.  It will stick there
forever, since there won't be anything to clear its ->name.name.

A bit of a complication: validate_request() drops and regains ->wq_mutex.
It actually ends up the most convenient place to stick the check into...

Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 fs/autofs4/waitq.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -257,6 +257,9 @@ static int validate_request(struct autof
 	struct autofs_wait_queue *wq;
 	struct autofs_info *ino;
 
+	if (sbi->catatonic)
+		return -ENOENT;
+
 	/* Wait in progress, continue; */
 	wq = autofs4_find_wait(sbi, qstr);
 	if (wq) {
@@ -289,6 +292,9 @@ static int validate_request(struct autof
 			if (mutex_lock_interruptible(&sbi->wq_mutex))
 				return -EINTR;
 
+			if (sbi->catatonic)
+				return -ENOENT;
+
 			wq = autofs4_find_wait(sbi, qstr);
 			if (wq) {
 				*wait = wq;
@@ -389,7 +395,7 @@ int autofs4_wait(struct autofs_sb_info *
 
 	ret = validate_request(&wq, sbi, &qstr, dentry, notify);
 	if (ret <= 0) {
-		if (ret == 0)
+		if (ret != -EINTR)
 			mutex_unlock(&sbi->wq_mutex);
 		kfree(qstr.name);
 		return ret;