CVE-2026-31705: ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment

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

ksmbd: fix out-of-bounds write in smb2getea() EA alignment

smb2getea() applies 4-byte alignment padding via memset() after writing each EA entry. The bounds check on buffreelen is performed before the value memcpy, but the alignment memset fires unconditionally afterward with no check on remaining space.

When the EA value exactly fills the remaining buffer (buffreelen == 0 after value subtraction), the alignment memset writes 1-3 NUL bytes past the buffreelen boundary. In compound requests where the response buffer is shared across commands, the first command (e.g., READ) can consume most of the buffer, leaving a tight remainder for the QUERYINFO EA response. The alignment memset then overwrites past the physical kvmalloc allocation into adjacent kernel heap memory.

Add a bounds check before the alignment memset to ensure buffreelen can accommodate the padding bytes.

This is the same bug pattern fixed by commit beef2634f81f ("ksmbd: fix potencial OOB in getfileallinfo() for compound requests") and commit fda9522ed6af ("ksmbd: fix OOB write in QUERYINFO for compound requests"), both of which added bounds checks before unconditional writes in QUERYINFO response handlers.