linux-user: Implement fchmodat2 syscall

The fchmodat2 syscall is new from Linux 6.6; it is like the
existing fchmodat syscall except that it takes a flags parameter.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3019
Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>
Message-ID: <[email protected]>
(cherry picked from commit 6a3e132a1be8c9e649967a4eb341d00731be7f51)
Signed-off-by: Michael Tokarev <[email protected]>

Author: pm215

linux-user/syscall.c

@@ -789,6 +789,10 @@ safe_syscall6(ssize_t, copy_file_range, int, infd, loff_t *, pinoff,
               int, outfd, loff_t *, poutoff, size_t, length,
               unsigned int, flags)
 #endif
+#if defined(TARGET_NR_fchmodat2) && defined(__NR_fchmodat2)
+safe_syscall4(int, fchmodat2, int, dfd, const char *, filename,
+              unsigned short, mode, unsigned int, flags)
+#endif
 
 /* We do ioctl like this rather than via safe_syscall3 to preserve the
  * "third argument might be integer or pointer or not present" behaviour of
@@ -10709,6 +10713,15 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
         ret = get_errno(fchmodat(arg1, p, arg3, 0));
         unlock_user(p, arg2, 0);
         return ret;
+#endif
+#if defined(TARGET_NR_fchmodat2) && defined(__NR_fchmodat2)
+    case TARGET_NR_fchmodat2:
+        if (!(p = lock_user_string(arg2))) {
+            return -TARGET_EFAULT;
+        }
+        ret = get_errno(safe_fchmodat2(arg1, p, arg3, arg4));
+        unlock_user(p, arg2, 0);
+        return ret;
 #endif
     case TARGET_NR_getpriority:
         /* Note that negative values are valid for getpriority, so we must