[PATCH AUTOSEL 4.9 2/8] ext2: Add more validity checks for inode counts

[Sasha Levin <sashal@kernel.org>]

From: Jan Kara <jack@suse.cz>

[ Upstream commit fa78f336937240d1bc598db817d638086060e7e9 ]

Add checks verifying number of inodes stored in the superblock matches
the number computed from number of inodes per group. Also verify we have
at least one block worth of inodes per group. This prevents crashes on
corrupted filesystems.

Reported-by: syzbot+d273f7d7f58afd93be48@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ext2/super.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 5ca1f73958b0..7cc83403ebe7 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -1042,9 +1042,10 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
 			sbi->s_frags_per_group);
 		goto failed_mount;
 	}
-	if (sbi->s_inodes_per_group > sb->s_blocksize * 8) {
+	if (sbi->s_inodes_per_group < sbi->s_inodes_per_block ||
+	    sbi->s_inodes_per_group > sb->s_blocksize * 8) {
 		ext2_msg(sb, KERN_ERR,
-			"error: #inodes per group too big: %lu",
+			"error: invalid #inodes per group: %lu",
 			sbi->s_inodes_per_group);
 		goto failed_mount;
 	}
@@ -1054,6 +1055,13 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
 	sbi->s_groups_count = ((le32_to_cpu(es->s_blocks_count) -
 				le32_to_cpu(es->s_first_data_block) - 1)
 					/ EXT2_BLOCKS_PER_GROUP(sb)) + 1;
+	if ((u64)sbi->s_groups_count * sbi->s_inodes_per_group !=
+	    le32_to_cpu(es->s_inodes_count)) {
+		ext2_msg(sb, KERN_ERR, "error: invalid #inodes: %u vs computed %llu",
+			 le32_to_cpu(es->s_inodes_count),
+			 (u64)sbi->s_groups_count * sbi->s_inodes_per_group);
+		goto failed_mount;
+	}
 	db_count = (sbi->s_groups_count + EXT2_DESC_PER_BLOCK(sb) - 1) /
 		   EXT2_DESC_PER_BLOCK(sb);
 	sbi->s_group_desc = kmalloc (db_count * sizeof (struct buffer_head *), GFP_KERNEL);
-- 
2.35.1