ocfs2: handle invalid dinode in ocfs2_group_extend

[BUG]
kernel BUG at fs/ocfs2/resize.c:308!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
RIP: 0010:ocfs2_group_extend+0x10aa/0x1ae0 fs/ocfs2/resize.c:308
Code: 8b8520ff ffff83f8 860f8580 030000e8 5cc3c1fe
Call Trace:
 ...
 ocfs2_ioctl+0x175/0x6e0 fs/ocfs2/ioctl.c:869
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x197/0x1e0 fs/ioctl.c:583
 x64_sys_call+0x1144/0x26a0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x93/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
 ...

[CAUSE]
ocfs2_group_extend() assumes that the global bitmap inode block
returned from ocfs2_inode_lock() has already been validated and
BUG_ONs when the signature is not a dinode. That assumption is too
strong for crafted filesystems because the JBD2-managed buffer path
can bypass structural validation and return an invalid dinode to the
resize ioctl.

[FIX]
Validate the dinode explicitly in ocfs2_group_extend(). If the global
bitmap buffer does not contain a valid dinode, report filesystem
corruption with ocfs2_error() and fail the resize operation instead of
crashing the kernel.

Link: https://lkml.kernel.org/r/20260401092303.3709187-1-gality369@gmail.com
Fixes: 10995aa ("ocfs2: Morph the haphazard OCFS2_IS_VALID_DINODE() checks.")
Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Gality369

fs/ocfs2/resize.c

@@ -303,9 +303,13 @@ int ocfs2_group_extend(struct inode * inode, int new_clusters)
 
 	fe = (struct ocfs2_dinode *)main_bm_bh->b_data;
 
-	/* main_bm_bh is validated by inode read inside ocfs2_inode_lock(),
-	 * so any corruption is a code bug. */
-	BUG_ON(!OCFS2_IS_VALID_DINODE(fe));
+	/* JBD-managed buffers can bypass validation, so treat this as corruption. */
+	if (!OCFS2_IS_VALID_DINODE(fe)) {
+		ret = ocfs2_error(main_bm_inode->i_sb,
+				  "Invalid dinode #%llu\n",
+				  (unsigned long long)OCFS2_I(main_bm_inode)->ip_blkno);
+		goto out_unlock;
+	}
 
 	if (le16_to_cpu(fe->id2.i_chain.cl_cpg) !=
 		ocfs2_group_bitmap_size(osb->sb, 0,