[BUG] description_show (MOST core) -- NULL-ptr-deref: the sysfs attribute derefs dev_get_drvdata() without a NULL check

[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/136-most-description_show-null-drvdata/

  Oops: general protection fault, probably for non-canonical address
0xdffffc0000000004: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
  RIP: 0010:description_show+0x46/0x80
  Call Trace:
   description_show+0x46/0x80
   dev_attr_show+0x58/0xc0
   sysfs_kf_seq_show+0x331/0x490
   seq_read_iter+0x4ef/0xe10
   vfs_read+0x582/0xa70
   ksys_read+0x150/0x270
  Kernel panic - not syncing: Fatal exception

Our reproducer.c is available upon request.

Happy to test a patch if that would help.

Regards,