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_begin() 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>
---
v2->v1:
- move check from ext4_resize_fs() to ext4_resize_begin().
fs/ext4/resize.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 90a941d20dff..8b70a4701293 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -53,6 +53,16 @@ int ext4_resize_begin(struct super_block *sb)
if (!capable(CAP_SYS_RESOURCE))
return -EPERM;
+ /*
+ * If the reserved GDT blocks is non-zero, the resize_inode feature
+ * should always be set.
+ */
+ if (EXT4_SB(sb)->s_es->s_reserved_gdt_blocks &&
+ !ext4_has_feature_resize_inode(sb)) {
+ ext4_error(sb, "resize_inode disabled but reserved GDT blocks non-zero");
+ return -EFSCORRUPTED;
+ }
+
/*
* 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
--
2.31.1
