CVE-2026-89671

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

nfsd: gate nfs3 setacl by argp->mask

nfsd3procsetacl() calls setposixacl() unconditionally for both

ACLTYPEACCESS and ACLTYPEDEFAULT, passing argp->acl_access and

argp->acl_default verbatim. The NFSv3 ACL decoder only populates

those pointers when the corresponding mask bit is set:

    nfs3svcdecodesetaclargs()

      if (args->mask & NFSACL)    decode into aclaccess

      if (args->mask & NFSDFACL)  decode into acldefault

      / otherwise the pointer stays NULL (pc_argzero) /

    nfsd3procsetacl()

      setposixacl(.., ACLTYPEACCESS,  argp->acl_access)

      setposixacl(.., ACLTYPEDEFAULT, argp->acl_default)

setposixacl(idmap, dentry, type, NULL) is the VFS "remove this

ACL type" operation. A NULL pointer that means "the client did not

send this arm" is therefore indistinguishable from "the client

asked to remove this ACL". A SETACL with mask=NFS_ACL silently

drops the directory's default ACL; mask=0 drops both.

The sibling nfsd3procgetacl() already consults argp->mask before

touching each arm; mirror that in setacl.

Fix by wrapping each setposixacl() call in the matching mask bit

check and initializing error to 0 before inode_lock so that a

request with neither bit set leaves the on-disk ACLs untouched and

returns nfsok. The outdrop_lock path and the unconditional

posixaclrelease() at out: are preserved; both NULL-tolerate the

skipped arms.