nix-daemon: Don't splice with len=SIZE_MAX

Currently, 'nix-daemon --stdio' is always failing for me, due to the
splice call always failing with (on a 32-bit host):

splice(0, NULL, 3, NULL, 4294967295, SPLICE_F_MOVE) = -1 EINVAL (Invalid argument)

With a bit of ftracing (and luck) the problem seems to be that splice()
always fails with EINVAL if the len cast as ssize_t is negative:
http://lxr.free-electrons.com/source/fs/read_write.c?v=4.4#L384

So use SSIZE_MAX instead of SIZE_MAX.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index f3ee0afc11e7..3b43ddfa16d5 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -23,6 +23,7 @@
 #include <pwd.h>
 #include <grp.h>
 #include <fcntl.h>
+#include <limits.h>
 
 #if __APPLE__ || __FreeBSD__
 #include <sys/ucred.h>
@@ -967,14 +968,14 @@ int main(int argc, char * * argv)
                     if (select(nfds, &fds, nullptr, nullptr, nullptr) == -1)
                         throw SysError("waiting for data from client or server");
                     if (FD_ISSET(s, &fds)) {
-                        auto res = splice(s, nullptr, STDOUT_FILENO, nullptr, SIZE_MAX, SPLICE_F_MOVE);
+                        auto res = splice(s, nullptr, STDOUT_FILENO, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
                         if (res == -1)
                             throw SysError("splicing data from daemon socket to stdout");
                         else if (res == 0)
                             throw EndOfFile("unexpected EOF from daemon socket");
                     }
                     if (FD_ISSET(STDIN_FILENO, &fds)) {
-                        auto res = splice(STDIN_FILENO, nullptr, s, nullptr, SIZE_MAX, SPLICE_F_MOVE);
+                        auto res = splice(STDIN_FILENO, nullptr, s, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
                         if (res == -1)
                             throw SysError("splicing data from stdin to daemon socket");
                         else if (res == 0)