linux-kernel - [PATCH 2/2] watch_queue: Actually free the watch

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Message-ID: <164786765966.1025645.8928727872789382885.stgit@warthog.procyon.org.uk>
Date:   Mon, 21 Mar 2022 13:00:59 +0000
From:   David Howells <dhowells@...hat.com>
To:     torvalds@...ux-foundation.org
Cc:     dhowells@...hat.com, fmdefrancesco@...il.com, jannh@...gle.com,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] watch_queue: Actually free the watch

free_watch() does everything barring actually freeing the watch object.  Fix
this by adding the missing kfree.

kmemleak produces a report something like the following.  Note that as an
address can be seen in the first word, the watch would appear to have gone
through call_rcu().

BUG: memory leak
unreferenced object 0xffff88810ce4a200 (size 96):
  comm "syz-executor352", pid 3605, jiffies 4294947473 (age 13.720s)
  hex dump (first 32 bytes):
    e0 82 48 0d 81 88 ff ff 00 00 00 00 00 00 00 00  ..H.............
    80 a2 e4 0c 81 88 ff ff 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff8214e6cc>] kmalloc include/linux/slab.h:581 [inline]
    [<ffffffff8214e6cc>] kzalloc include/linux/slab.h:714 [inline]
    [<ffffffff8214e6cc>] keyctl_watch_key+0xec/0x2e0 security/keys/keyctl.c:1800
    [<ffffffff8214ec84>] __do_sys_keyctl+0x3c4/0x490 security/keys/keyctl.c:2016
    [<ffffffff84493a25>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    [<ffffffff84493a25>] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
    [<ffffffff84600068>] entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixes: c73be61cede5 ("pipe: Add general notification queue support")
Reported-and-tested-by: syzbot+6e2de48f06cdb2884bfc@...kaller.appspotmail.com
Signed-off-by: David Howells <dhowells@...hat.com>
---

 kernel/watch_queue.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index 5848d4795816..3990e4df3d7b 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -395,6 +395,7 @@ static void free_watch(struct rcu_head *rcu)
 	put_watch_queue(rcu_access_pointer(watch->queue));
 	atomic_dec(&watch->cred->user->nr_watches);
 	put_cred(watch->cred);
+	kfree(watch);
 }
 
 static void __put_watch(struct kref *kref)