On 22/05/26 03:32PM, Zhang Yi wrote:
> 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.
Your reasoning looks correct to me.
>
> 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;
> }
I think we should do this check in ext4_resize_begin(), i.e.
if ext4_has_feature_resize_inode() is false and es->s_reserved_gdt_blocks is
non-zero, then we should straight away mark and return error.
Later (not as part of this patch/fix) maybe if we detect this problem, we could
use helpers like ext4_update_super() to fix this mismatch problem in kernel
during mount itself. But I think this is not absolutely necessary,
as kernel already during mount outputs a warning and ask for running e2fsck.
Thougts?
-ritesh
>
> if ((!resize_inode && !meta_bg) || n_blocks_count == o_blocks_count) {
> --
> 2.31.1
>
