Stefan, On Mon, Mar 21, 2011 at 11:49 PM, Stefan Puiu <stefan.puiu@xxxxxxxxx> wrote: > Hi, > > It seems sendto() can return EACCES for UDP as well; the current man > page in git only says it can return EACCES for Unix sockets: > > EACCES > (For UNIX domain sockets, which are identified by pathname) Write > permission is denied on the destination socket file, or > search permission is denied for one of the directories > the path prefix. (See path_resolution(7).) > > I was able to make sendto() return EACCES if I try to send from > 192.168.1.1/24 to 192.168.1.0. I think the relevant code (in kernel > 2.6.38, but also present in 2.6.7 and 2.6.32, the 2 kernels we use) is > this (net/ipv4/udp.c, udp_sendmsg()): > > 910 err = -EACCES; > 911 if ((rt->rt_flags & RTCF_BROADCAST) && > 912 !sock_flag(sk, SOCK_BROADCAST)) > 913 goto out; > > So I guess if the kernel finds a route to the destination and it's a > broadcast route (and the socket doesn't have the broadcast flag), then > it returns EACCES. > > I can verify the behavior with a very simple program (attached). I've > run it on my Ubuntu 10.10 (2.6.35 kernel) and got this: > > stefan@spuiu-vml2:~/src/test/broadcast$ ./broadcast_test 10.205.20.94 > 10.205.20.1 > sendto() returned 4 > stefan@spuiu-vml2:~/src/test/broadcast$ ./broadcast_test 10.205.20.94 > 10.205.20.0 > sendto() returned negative, errno: 13/Permission denied > > (10.205.20.94 is my local IP, of course). > > How about updating the send.2 page like this? > > diff --git a/man2/send.2 b/man2/send.2 > index 69287fb..4d2faed 100644 > --- a/man2/send.2 > +++ b/man2/send.2 > @@ -288,6 +288,8 @@ or search permission is denied for one of the directories > the path prefix. > (See > .BR path_resolution (7).) > +(For UDP sockets) An attempt was made to sendto() to a > +network/broadcast address like it was a unicast address. > .TP > .BR EAGAIN " or " EWOULDBLOCK > .\" Actually EAGAIN on Linux I applied a slightly reworded (but essentially the same) patch: ===== @@ -288,6 +288,9 @@ or search permission is denied for one of the directories the path prefix. (See .BR path_resolution (7).) +.sp +(For UDP sockets) An attempt was made to send to a +network/broadcast address as though it was a unicast address. .TP .BR EAGAIN " or " EWOULDBLOCK .\" Actually EAGAIN on Linux ===== Will be in 3.40. thanks! Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
