[PATCH 3.16 188/328] ext4: prevent online resize with backup superblock

Ben Hutchings
2018-12-09T22:16:50Z

From: Theodore Ts'o <tytso@mit.edu>

commit 011fa99404bea3f5d897c4983f6bd51170e3b18f upstream.

Prevent BUG or corrupted file systems after the following:

mkfs.ext4 /dev/vdc 100M
mount -t ext4 -o sb=40961 /dev/vdc /vdc
resize2fs /dev/vdc

We previously prevented online resizing using the old resize ioctl.
Move the code to ext4_resize_begin(), so the check applies for all of
the resize ioctl's.

Reported-by: Maxim Malkov <malkov@ispras.ru>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/resize.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)

--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -24,6 +24,18 @@ int ext4_resize_begin(struct super_block
return -EPERM;

/*
+ * If we are not using the primary superblock/GDT copy don't resize,
+ * because the user tools have no way of handling this. Probably a
+ * bad time to do it anyways.
+ */
+ if (EXT4_SB(sb)->s_sbh->b_blocknr !=
+ le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block)) {
+ ext4_warning(sb, "won't resize using backup superblock at %llu",
+ (unsigned long long)EXT4_SB(sb)->s_sbh->b_blocknr);
+ return -EPERM;
+ }
+
+ /*
* We are not allowed to do online-resizing on a filesystem mounted
* with error, because it can destroy the filesystem easily.
*/
@@ -758,18 +770,6 @@ static int add_new_gdb(handle_t *handle,
"EXT4-fs: ext4_add_new_gdb: adding group block %lu\n",
gdb_num);

- /*
- * If we are not using the primary superblock/GDT copy don't resize,
- * because the user tools have no way of handling this. Probably a
- * bad time to do it anyways.
- */
- if (EXT4_SB(sb)->s_sbh->b_blocknr !=
- le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block)) {
- ext4_warning(sb, "won't resize using backup superblock at %llu",
- (unsigned long long)EXT4_SB(sb)->s_sbh->b_blocknr);
- return -EPERM;
- }
-
gdb_bh = sb_bread(sb, gdblock);
if (!gdb_bh)
return -EIO;