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Date: Thu, 26 May 2022 15:32:22 +0800 From: Zhang Yi <yi.zhang@...wei.com> To: <linux-ext4@...r.kernel.org> CC: <tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>, <ritesh.list@...il.com>, <yi.zhang@...wei.com>, <yukuai3@...wei.com>, <lilingfeng3@...wei.com> Subject: [PATCH] ext4: add reserved GDT blocks check 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@...wei.com> --- 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
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