linux-kernel - [PATCH -next] fs: sysv: check sbi->s_firstdatazone in complete_read

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Date:   Wed, 30 Mar 2022 18:42:15 +0800
From:   Liu Shixin <liushixin2@...wei.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     <linux-kernel@...r.kernel.org>, Liu Shixin <liushixin2@...wei.com>
Subject: [PATCH -next] fs: sysv: check sbi->s_firstdatazone in complete_read_super

sbi->s_firstinodezone is initialized to 2 and sbi->s_firstdatazone is read
from sbd. There's no guarantee that sbi->s_firstdatazone must bigger than
sbi->s_firstinodezone. If sbi->s_firstdatazone less than 2, the filesystem
can still be mounted unexpetly. At this point, sbi->s_ninodes flip to very
large value and this filesystem is broken. We can observe this by
executing 'df' command. When we execute, we will get an error message:
	"sysv_count_free_inodes: unable to read inode table"

Signed-off-by: Liu Shixin <liushixin2@...wei.com>
---
 fs/sysv/super.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/sysv/super.c b/fs/sysv/super.c
index d1def0771a40..3365a30dc1e0 100644
--- a/fs/sysv/super.c
+++ b/fs/sysv/super.c
@@ -312,7 +312,9 @@ static int complete_read_super(struct super_block *sb, int silent, int size)
 	sbi->s_firstinodezone = 2;
 
 	flavour_setup[sbi->s_type](sbi, &sb->s_max_links);
-	
+	if (sbi->s_firstdatazone < sbi->s_firstinodezone)
+		return 0;
+
 	sbi->s_ndatazones = sbi->s_nzones - sbi->s_firstdatazone;
 	sbi->s_inodes_per_block = bsize >> 6;
 	sbi->s_inodes_per_block_1 = (bsize >> 6)-1;
-- 
2.25.1