ksmbd: validate inherited ACE SID length

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: validate inherited ACE SID length

smb_inherit_dacl() walks the parent directory DACL loaded from the

security descriptor xattr. It verifies that each ACE contains the fixed

SID header before using it, but does not verify that the variable-length

SID described by sid.num_subauth is fully contained in the ACE.

A malformed inheritable ACE can advertise more subauthorities than are

present in the ACE. compare_sids() may then read past the ACE.

smb_set_ace() also clamps the copied destination SID, but used the

unchecked source SID count to compute the inherited ACE size. That could

advance the temporary inherited ACE buffer pointer and nt_size accounting

past the allocated buffer.

Fix this by validating the parent ACE SID count and SID length before

using the SID during inheritance. Compute the inherited ACE size from the

copied SID so the size matches the bounded destination SID. Reject the

inherited DACL if size accumulation would overflow smb_acl.size or the

security descriptor allocation size.