[BUG] general protection fault in sysfs_do_create_link_sd

[Farhad Alemi]

Hello,

As part of the kernel research at ASU's SEFCOM
lab, we hit the crash below. Crash reports can be found here:

  https://github.com/farhad-alemi/public_bug_reports/tree/main/188-general-protection-fault-in-sysfs-do-create-link-sd/

  Oops: general protection fault, probably for non-canonical address
0xdffffc0000000006: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
  RIP: 0010:sysfs_do_create_link_sd+0x4b/0x110 fs/sysfs/symlink.c:35
  Call Trace:
   sysfs_do_create_link_sd+0x4b/0x110 fs/sysfs/symlink.c:35
   nfs_sysfs_link_rpc_client+0x3a3/0x590 fs/nfs/sysfs.c:343
   nfs_init_server fs/nfs/client.c:770 [inline]
   nfs_create_server+0x7e8/0x2110 fs/nfs/client.c:1155
   nfs3_create_server+0x1e/0x180 fs/nfs/nfs3client.c:56
   nfs_try_get_tree+0x1fa/0x11a0 fs/nfs/super.c:981
   vfs_get_tree+0x8f/0x290 fs/super.c:1754
   do_new_mount+0x341/0xd80 fs/namespace.c:3834

Our reproducer.c is available upon request.

Happy to test a patch if that would help.

Regards,