CVE-2026-99110: smb: client: fix heap overflow in cifs_do_set_acl()

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

smb: client: fix heap overflow in cifsdosetacl()

cifssetacl() validates ACL size using posixaclxattrsize():

4 + (count 8) // 4-byte header + 8 bytes per ACE

cifsdosetacl() then calls posixacltocifs() to write the CIFS wire format into the same buffer:

6 + (count 10) // 6-byte header + 10 bytes per ACE

An ACL that passes the xattr-based check in cifssetacl() can overflow the heap when posixacltocifs() writes the larger CIFS format.

Validate the CIFS format size against the remaining buffer space and USHRTMAX before converting--datacount is u16, so sizes above USHRTMAX truncate the on-wire packet length, causing the server to apply a partial ACL. Replace MaxDataCount = 1000 with min(CIFSMaxBufSize, USHRTMAX).