7.94/95 break SCTP listening when stdin=/dev/null

[edsantiago]

Describe the bug
Identical to #2685, except with SCTP

To Reproduce
Terminal 1:

# modprobe sctp
# nc -4 --sctp -l -p 5000 </dev/null

Terminal 2:

# echo test | nc -4 --sctp 127.0.0.1 5000

Expected behavior
Expect terminal 1 to see test. (Removing the redirection makes it work)

Version info (please complete the following information):

• OS: Fedora 39
• Output of ncat --version: Ncat: Version 7.95

[Luap99]

strace output with /dev/null on stdin

accept(3, {sa_family=AF_INET, sin_port=htons(44148), sin_addr=inet_addr("127.0.0.1")}, [128 => 16]) = 4
close(3)                                = 0
fcntl(4, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
pselect6(5, [0 4], [], NULL, NULL, NULL) = 2 (in [0 4])
read(0, "", 8192)                       = 0
exit_group(0)                           = ?
+++ exited with 0 +++

with /dev/zero on stdin:

...
accept(3, {sa_family=AF_INET, sin_port=htons(54661), sin_addr=inet_addr("127.0.0.1")}, [128 => 16]) = 4
close(3)                                = 0
fcntl(4, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
pselect6(5, [0 4], [], NULL, NULL, NULL) = 2 (in [0 4])
read(0, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192
fcntl(4, F_GETFL)                       = 0x802 (flags O_RDWR|O_NONBLOCK)
fcntl(4, F_SETFL, O_RDWR)               = 0
sendto(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192, 0, NULL, 0) = -1 EPIPE (Broken pipe)
--- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=74438, si_uid=1000} ---
fcntl(4, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
close(4)                                = 0
read(0, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192
exit_group(0)             

and when it is attached to the terminal (working):

accept(3, {sa_family=AF_INET, sin_port=htons(32795), sin_addr=inet_addr("127.0.0.1")}, [128 => 16]) = 4
close(3)                                = 0
fcntl(4, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
pselect6(5, [0 4], [], NULL, NULL, NULL) = 1 (in [4])
recvfrom(4, "test\n", 8192, 0, NULL, NULL) = 5
write(1, "test\n", 5test
)                   = 5
pselect6(5, [0 4], [], NULL, NULL, NULL) = 1 (in [4])
recvfrom(4, "", 8192, 0, NULL, NULL)    = 0
close(4)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++

So if there is data on stdin (or it was closed) it will exit right away before printing the data it got.