CVE-2026-97559

In the Linux kernel, the following vulnerability has been resolved: smb: client: fail DACL rewrite when the new DACL exceeds 64K replace_sids_and_copy_aces() and set_chmod_dacl() accumulate the size of the DACL they build in a u16. That accumulator can wrap. validate_dacl() caps num_aces at (dacl_size - sizeof(struct smb_acl)) / 20, i.e. 3276 for a maximally sized DACL, while each rewritten ACE can grow to sizeof(struct smb_ace) (76 bytes) once its SID is replaced with one carrying SID_MAX_SUB_AUTHORITIES sub-authorities. The worst case is therefore sizeof(struct smb_acl) + 3276 * 76 = 248984 bytes, far beyond what a u16 can hold. A wraparound is reached with 863 ACEs. After the wraparound, ndacl_ptr->size becomes meaningless and the offset will point anywhere in the ACE array. As a result, we will see corruption of the DACL, which then gets sent to the server. This is not an out-of-bounds write as the allocation now covers the worst-case expansion, so writes will always go into the buffer. Adjust the code to use a u32 internally and return -EOVERFLOW in the overflow case. The operation must be refused, because a DACL can only hold 2^16-1 bytes on the wire and larger DACLs cannot b