Fix crash when handling socket closure early

When the MCTP daemon closes the socket, the event loop may still
deliver `EPOLLIN` alongside `POLLHUP`. Previously, the callback did not
explicitly check for `POLLHUP` before attempting to receive data via
`recvMsg()`.

This led to a scenario where `recvMsg()` was called on a socket that
had already been closed, causing undefined behavior or memory
corruption (e.g., during buffer allocation or cleanup). While
`recvMsg()` returned a failure code (`PLDM_REQUESTER_RECV_FAIL`), the
subsequent call to `io.get_event().exit(0)` would result in a crash due
to the corrupted state.

This change adds an early check for `POLLHUP` (and `POLLERR`) at the
beginning of the IO callback and exits the event loop immediately when
detected. This prevents any further I/O operations on a dead socket and
ensures a clean shutdown without triggering undefined behavior.

Here is the gdb backtrace & its corresponding source code[1]:
```
Core was generated by `/usr/bin/pldmd'.
Program terminated with signal SIGABRT, Aborted.
    #0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=<optimized out>) at pthread_kill.c:44
    #1  0x763c9344 in __GI_raise (sig=sig@entry=6) at /usr/src/debug/glibc/2.39+git/sysdeps/posix/raise.c:26
    #2  0x763b3f80 in __GI_abort () at abort.c:79
    openbmc#3  0x764026e4 in __libc_message_impl (fmt=0x764e8050 "%s\n") at /usr/src/debug/glibc/2.39+git/sysdeps/posix/libc_fatal.c:132
    openbmc#4  0x76419d8c in malloc_printerr (str=<optimized out>) at malloc.c:5772
    openbmc#5  0x7641a950 in _int_free_create_chunk (av=0x20, av@entry=0x764f05fc <main_arena>, p=0x1000, p@entry=0x1c7f898, size=<optimized out>, size@entry=152, nextchunk=nextchunk@entry=0x1c7f930, nextsize=nextsize@entry=32) at malloc.c:4735
    openbmc#6  0x7641bf94 in _int_free_merge_chunk (av=0x764f05fc <main_arena>, p=0x1c7f898, size=152) at malloc.c:4700
    openbmc#7  0x7641c298 in _int_free (av=<optimized out>, p=<optimized out>, have_lock=<optimized out>, have_lock@entry=0) at malloc.c:4646
    openbmc#8  0x7641ec20 in __GI___libc_free (mem=mem@entry=0x1c7f8a0) at malloc.c:3398
    openbmc#9  0x7681a3b8 in source_free (s=0x1c7f8a0) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-event/sd-event.c:1125
    openbmc#10 0x7681e6d8 in event_source_free (s=<optimized out>) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-event/sd-event.c:2590
    openbmc#11 sd_event_source_unref (p=<optimized out>) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-event/sd-event.c:2595
    openbmc#12 0x767eb624 in sd_bus_detach_event (bus=<optimized out>) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-bus/sd-bus.c:3887
    openbmc#13 0x767e0888 in sd_bus_close (bus=0x1bb4950) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-bus/sd-bus.c:1772
    openbmc#14 sd_bus_close (bus=0x1bb4950) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-bus/sd-bus.c:1759
    openbmc#15 0x767eea30 in quit_callback (event=<optimized out>, userdata=0x1bb4950) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-bus/sd-bus.c:3726
    openbmc#16 0x76826288 in source_dispatch (s=s@entry=0x1c1d718) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-event/sd-event.c:4227
    openbmc#17 0x7682697c in dispatch_exit (e=0x1bb42c0) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-event/sd-event.c:4349
    openbmc#18 sd_event_dispatch (e=<optimized out>, e@entry=0x1bb42c0) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-event/sd-event.c:4801
    openbmc#19 0x768282c8 in sd_event_run (e=<optimized out>, timeout=<optimized out>) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-event/sd-event.c:4869
    openbmc#20 0x76828558 in sd_event_loop (e=<optimized out>) at /usr/src/debug/systemd/255.4/src/libsystemd/sd-event/sd-event.c:4891
    openbmc#21 0x7678f514 in sdeventplus::internal::SdEventImpl::sd_event_loop (event=<optimized out>, this=<optimized out>) at /usr/src/debug/sdeventplus/0.1+git/src/sdeventplus/internal/sdevent.cpp:86
    openbmc#22 sdeventplus::Event::loop (this=this@entry=0x7ed298e0) at /usr/src/debug/sdeventplus/0.1+git/src/sdeventplus/event.cpp:81
    openbmc#23 0x004f904c in main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/pldm/1.0+git/pldmd/pldmd.cpp:433
```
[1]: https://github.com/ibm-openbmc/pldm/blob/424d866fe97b20343e7733fcab462e0ea1035379/pldmd/pldmd.cpp#L433

Change-Id: Idc5fb2cb849f2af7c12b67cdd509d81b2587c8ba
Signed-off-by: Manojkiran Eda <[email protected]>

Author: manojkiraneda

pldmd/pldmd.cpp

@@ -347,7 +347,14 @@ int main(int argc, char** argv)
                      fwManager.get(), platformManager.get()});
     auto callback = [verbose, &invoker, &reqHandler, &fwManager, &pldmTransport,
                      TID](IO& io, int fd, uint32_t revents) mutable {
-        if (!(revents & EPOLLIN))
+        if (revents & (POLLHUP | POLLERR))
+        {
+            warning("Transport Socket hang-up or error. IO Exiting.");
+            io.get_event().exit(0);
+            return;
+        }
+
+        else if (!(revents & EPOLLIN))
         {
             return;
         }