linux-kernel - [PATCH 1/2] fs/efivarfs: restrict inode permissions

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Message-Id: <20180215182208.35003-2-joe.konno@linux.intel.com>
Date:   Thu, 15 Feb 2018 10:22:07 -0800
From:   Joe Konno <joe.konno@...ux.intel.com>
To:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     ard.biesheuvel@...aro.org, matthew.garrett@...ula.com,
        jk@...abs.org, ak@...ux.intel.com, tony.luck@...el.com
Subject: [PATCH 1/2] fs/efivarfs: restrict inode permissions

From: Joe Konno <joe.konno@...el.com>

Efivarfs nodes are created with group and world readable permissions.
Reading certain EFI variables trigger SMIs. So, this is a potential DoS
surface.

Make permissions more restrictive-- only the owner may read or write to
created inodes.

Suggested-by: Andi Kleen <ak@...ux.intel.com>
Reported-by: Tony Luck <tony.luck@...el.com>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Matthew Garrett <matthew.garrett@...ula.com>
Cc: Jeremy Kerr <jk@...abs.org>
Cc: linux-efi@...r.kernel.org
Cc: stable@...r.kernel.org
Signed-off-by: Joe Konno <joe.konno@...el.com>
---
 fs/efivarfs/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index 5b68e4294faa..ca98c4e31eb7 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -145,7 +145,7 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 
 	name[len + EFI_VARIABLE_GUID_LEN+1] = '\0';
 
-	inode = efivarfs_get_inode(sb, d_inode(root), S_IFREG | 0644, 0,
+	inode = efivarfs_get_inode(sb, d_inode(root), S_IFREG | 0600, 0,
 				   is_removable);
 	if (!inode)
 		goto fail_name;
@@ -207,7 +207,7 @@ static int efivarfs_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_d_op		= &efivarfs_d_ops;
 	sb->s_time_gran         = 1;
 
-	inode = efivarfs_get_inode(sb, NULL, S_IFDIR | 0755, 0, true);
+	inode = efivarfs_get_inode(sb, NULL, S_IFDIR | 0700, 0, true);
 	if (!inode)
 		return -ENOMEM;
 	inode->i_op = &efivarfs_dir_inode_operations;
-- 
2.14.1