POSTCR-f20c712f167acd692240350179d4d98d33971375-1: pre-existing:                       
extattr_list_{fd,file,link} with nbytes > SSIZE_MAX makes uio_resid negative,          
which gets past the IOSIZE_MAX check and trips the uiomove() KASSERT (panic            
triggerable by an unprivileged user on INVARIANTS kernels)                             
                                                                                       
This bug was already present before this commit. The commit moves the affected         
code without changing its behaviour.                                                   
                                                                                       
- user_extattr_list_fd() and user_extattr_list_path() set auio.uio_resid =             
nbytes without checking nbytes first. This code used to live in                        
sys_extattr_list_fd and the old static user_extattr_list_path.                         
- extattr_list_vp() then checks only auiop->uio_resid > IOSIZE_MAX. A negative         
ssize_t passes that check.                                                             
- Trigger: create a file on UFS2, set one user-namespace attribute, then call          
extattr_list_file(path, EXTATTR_NAMESPACE_USER, buf, SIZE_MAX).                        
ffs_listextattr() calls uiomove(), which hits KASSERT(uio->uio_resid >= 0). On         
INVARIANTS kernels this is a panic that an unprivileged user can trigger.              
- On kernels without INVARIANTS, copyout still bounds the copy, but the resid          
arithmetic and td_retval come out wrong.                                               
- Origin: commit 6453d4240f6b ("vfs: Export exattr methods to reuse by                 
Linuxulator"). Before that commit, extattr_list_vp() checked the size_t nbytes >       
IOSIZE_MAX. That commit replaced it with the ssize_t uio_resid comparison.             
- The Linuxulator caller is not affected because it clamps the size to                 
LINUX_XATTR_LIST_MAX.                                                                  
- Suggested fix: check nbytes > IOSIZE_MAX in the two user_ wrappers, as the           
get/set paths already do (vfs_extattr.c:180 and :372).