linux-kernel - [PATCH] exfat: tighten down num

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Message-ID: <89603.1581722921@turing-police>
Date:   Fri, 14 Feb 2020 18:28:41 -0500
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Namjae Jeon <linkinjeon@...il.com>, Sasha Levin <sashal@...nel.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, hch@....de, sj1557.seo@...sung.com,
        pali.rohar@...il.com, arnd@...db.de, namjae.jeon@...sung.com,
        viro@...iv.linux.org.uk
Subject: [PATCH] exfat: tighten down num_fats check

Change the test for num_fats from != 0 to a check for specifically 1.

Although it's theoretically possible that num_fats == 2 for a TexFAT volume (or
an implementation that doesn't do the full TexFAT but does support 2 FAT
tables), the rest of the code doesn't currently DTRT if it's 2 (in particular,
not handling the case of ActiveFat pointing at the second FAT area), so we'll
disallow that as well, as well as dealing with corrupted images that have a
trash non-zero value.

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@...edu>

--- a/fs/exfat/super.c	2020-02-14 17:45:02.262274632 -0500
+++ b/fs/exfat/super.c	2020-02-14 17:46:37.200343723 -0500
@@ -450,7 +450,7 @@ static int __exfat_fill_super(struct sup
 	}

 	p_bpb = (struct pbr64 *)p_pbr;
-	if (!p_bpb->bsx.num_fats) {
+	if (p_bpb->bsx.num_fats  != 1) {
 		exfat_msg(sb, KERN_ERR, "bogus number of FAT structure");
 		ret = -EINVAL;
 		goto free_bh;

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