We capture a NULL pointer issue when resizing a corrupt ext4 image which
is freshly clear resize_inode feature (not run e2fsck). It could be
simply reproduced by following steps. The problem is because of the
resize_inode feature was cleared, and it will convert the filesystem to
meta_bg mode in ext4_resize_fs(), but the es->s_reserved_gdt_blocks was
not reduced to zero, so could we mistakenly call reserve_backup_gdb()
and passing an uninitialized resize_inode to it when adding new group
descriptors.
mkfs.ext4 /dev/sda 3G
tune2fs -O ^resize_inode /dev/sda #forget to run requested e2fsck
mount /dev/sda /mnt
resize2fs /dev/sda 8G
========
BUG: kernel NULL pointer dereference, address: 0000000000000028
CPU: 19 PID: 3243 Comm: resize2fs Not tainted 5.18.0-rc7-00001-gfde086c5ebfd #748
...
RIP: 0010:ext4_flex_group_add+0xe08/0x2570
...
Call Trace:
<TASK>
ext4_resize_fs+0xbec/0x1660
__ext4_ioctl+0x1749/0x24e0
ext4_ioctl+0x12/0x20
__x64_sys_ioctl+0xa6/0x110
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f2dd739617b
========
The fix is simple, add a check in ext4_resize_fs() to make sure that the
es->s_reserved_gdt_blocks is zero when the resize_inode feature is
disabled.
Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
fs/ext4/resize.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 90a941d20dff..5791eb7c0761 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -2031,6 +2031,9 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
ext4_warning(sb, "Error opening resize inode");
return PTR_ERR(resize_inode);
}
+ } else if (es->s_reserved_gdt_blocks) {
+ ext4_error(sb, "resize_inode disabled but reserved GDT blocks non-zero");
+ return -EFSCORRUPTED;
}
if ((!resize_inode && !meta_bg) || n_blocks_count == o_blocks_count) {
--
2.31.1
