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From:   "Valdis =?utf-8?Q?Kl=c4=93tnieks?=" <valdis.kletnieks@vt.edu>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Sasha Levin <alexander.levin@microsoft.com>,
        Christoph Hellwig <hch@infradead.org>
cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] drivers/staging/exfat - by default, prohibit mount of fat/vfat
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Date:   Fri, 30 Aug 2019 12:42:39 -0400
Message-ID: <245727.1567183359@turing-police>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Concerns have been raised about the exfat driver accidentally mounting
fat/vfat file systems.  Add an extra configure option to help prevent that.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>

diff --git a/drivers/staging/exfat/Kconfig b/drivers/staging/exfat/Kconfig
index 78b32aa2ca19..1df177b1dc72 100644
--- a/drivers/staging/exfat/Kconfig
+++ b/drivers/staging/exfat/Kconfig
@@ -4,6 +4,14 @@ config EXFAT_FS
 	help
 	  This adds support for the exFAT file system.
 
+config EXFAT_DONT_MOUNT_VFAT
+	bool "Prohibit mounting of fat/vfat filesysems by exFAT"
+	default y
+	help
+	  By default, the exFAT driver will only mount exFAT filesystems, and refuse
+	  to mount fat/vfat filesystems.  Set this to 'n' to allow the exFAT driver
+	  to mount these filesystems.
+
 config EXFAT_DISCARD
 	bool "enable discard support"
 	depends on EXFAT_FS
diff --git a/drivers/staging/exfat/exfat_super.c b/drivers/staging/exfat/exfat_super.c
index 5b5c2ca8c9aa..7fdb5b8bc928 100644
--- a/drivers/staging/exfat/exfat_super.c
+++ b/drivers/staging/exfat/exfat_super.c
@@ -486,10 +486,16 @@ static int ffsMountVol(struct super_block *sb)
 			break;
 
 	if (i < 53) {
+#ifdef CONFIG_EXFAT_DONT_MOUNT_VFAT
+		ret = -EINVAL;
+		printk(KERN_INFO "EXFAT: Attempted to mount VFAT filesystem\n");
+		goto out;
+#else
 		if (GET16(p_pbr->bpb + 11)) /* num_fat_sectors */
 			ret = fat16_mount(sb, p_pbr);
 		else
 			ret = fat32_mount(sb, p_pbr);
+#endif
 	} else {
 		ret = exfat_mount(sb, p_pbr);
 	}