linux-kernel - [PATCH] dm: verity: fix module param permissions

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Message-Id: <20210512111421.1828191-1-john@metanate.com>
Date:   Wed, 12 May 2021 12:14:21 +0100
From:   John Keeping <john@...anate.com>
To:     dm-devel@...hat.com
Cc:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        linux-kernel@...r.kernel.org, John Keeping <john@...anate.com>
Subject: [PATCH] dm: verity: fix module param permissions

The third parameter of module_param() is permissions for the sysfs node
but it looks like it is being used as the initial value of the parameter
here.  In fact, false here equates to omitting the file from sysfs and
does not affect the value of require_signatures.

Making the parameter writable is not simple because going from
false->true is fine but it should not be possible to remove the
requirement to verify a signature.  But it can be useful to inspect the
value of this parameter from userspace, so change the permissions to
make a read-only file in sysfs.

Signed-off-by: John Keeping <john@...anate.com>
---
 drivers/md/dm-verity-verify-sig.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-verity-verify-sig.c b/drivers/md/dm-verity-verify-sig.c
index 29385dc470d5..db61a1f43ae9 100644
--- a/drivers/md/dm-verity-verify-sig.c
+++ b/drivers/md/dm-verity-verify-sig.c
@@ -15,7 +15,7 @@
 #define DM_VERITY_VERIFY_ERR(s) DM_VERITY_ROOT_HASH_VERIFICATION " " s

 static bool require_signatures;
-module_param(require_signatures, bool, false);
+module_param(require_signatures, bool, 0444);
 MODULE_PARM_DESC(require_signatures,
 		"Verify the roothash of dm-verity hash tree");

-- 
2.31.1