UBUNTU-CVE-2026-97555: High severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix heap overflow in DACL owner/group rewrite When idmodetocifsacl rewrites an existing DACL, it allocates a buffer sized according to the on-disk DACL length reported by daclptr->size. However, replacesidsandcopyaces may rewrite each ACE with a new owner/group SID obtained from the cifs.idmap upcall. Those SIDs can have up to SIDMAXSUBAUTHORITIES (15) sub-authorities, making each ACE up to 76 bytes (sizeof(struct smbace)). If the original DACL contains short SIDs (e.g., 1 sub-authority) while the replacement SIDs are long, the rewritten ACEs overflow the allocation. Fix this by always budgeting for worst-case SID expansion: allocate sizeof(struct smbacl) plus numaces sizeof(struct smbace), which covers the smbacl header and room for every ACE at maximum SID size. This replaces the previous split logic that used daclptr->size for cifsacl mounts but numaces sizeof(struct smbace) for modefromsid mounts: both paths can trigger the same rewrite and need the same headroom. KASAN reports this as: BUG: KASAN: slab-out-of-bounds in buildsecdesc+0x1e8a/0x2680 [cifs] Write of size 4 at addr ffff8881a5e25374 by task chown/5298 ... The buggy address is located 0 bytes to the right of allocated 884-byte region [ffff8881a5e25000, ffff8881a5e25374)