jfs: Fix fortify moan in symlink

JFS has in jfs_incore.h:

      /* _inline may overflow into _inline_ea when needed */
      /* _inline_ea may overlay the last part of
       * file._xtroot if maxentry = XTROOTINITSLOT
       */
      union {
        struct {
          /* 128: inline symlink */
          unchar _inline[128];
          /* 128: inline extended attr */
          unchar _inline_ea[128];
        };
        unchar _inline_all[256];

and currently the symlink code copies into _inline;
if this is larger than 128 bytes it triggers a fortify warning of the
form:

  memcpy: detected field-spanning write (size 132) of single field
     "ip->i_link" at fs/jfs/namei.c:950 (size 18446744073709551615)

when it's actually OK.

Copy it into _inline_all instead.

Reported-by: syzbot+5fc38b2ddbbca7f5c680@syzkaller.appspotmail.com
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

fs/jfs/namei.c

@@ -946,7 +946,7 @@ static int jfs_symlink(struct user_namespace *mnt_userns, struct inode *dip,
 	if (ssize <= IDATASIZE) {
 		ip->i_op = &jfs_fast_symlink_inode_operations;
 
-		ip->i_link = JFS_IP(ip)->i_inline;
+		ip->i_link = JFS_IP(ip)->i_inline_all;
 		memcpy(ip->i_link, name, ssize);
 		ip->i_size = ssize - 1;