httpd: treat errors from stdin correctly.

Fron bug report:

If a CGI or proxied connection is rudely aborted (SIG_{KILL,BUS,SEGV})
then httpd will spin madly the poll loop in:

networking/httpd.c:1080
cgi_io_loop_and_exit()

Upon investigation I found that pfd[0].revents == 0x0018 (POLLHUP|POLLERR),
which leads to empty read, but the pfd[0].fd (STDIN_FILENO) is left open,
and in the FD list given to poll() which immediately returns to once
again inform the loop of (POLLHUP|POLLERR) condition of pfd[0].fd.
This continues until pfd[FROM_CGI].revents != 0

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/networking/httpd.c b/networking/httpd.c
index cef9b8b..1433313 100644 (file)
--- a/networking/httpd.c
+++ b/networking/httpd.c
@@ -1105,16 +1105,21 @@ static NOINLINE void cgi_io_loop_and_exit(int fromCgi_rd, int toCgi_wr, int post
        /* NB: breaking out of this loop jumps to log_and_exit() */
        out_cnt = 0;
        while (1) {
-               memset(pfd, 0, sizeof(pfd));
+               /* Note: even pfd[0].events == 0 won't prevent
+                * revents == POLLHUP|POLLERR reports from closed stdin.
+                * This works: */
+               pfd[0].fd = -1;
 
                pfd[FROM_CGI].fd = fromCgi_rd;
                pfd[FROM_CGI].events = POLLIN;
 
-               if (toCgi_wr) {
-                       pfd[TO_CGI].fd = toCgi_wr;
-                       if (hdr_cnt > 0) {
-                               pfd[TO_CGI].events = POLLOUT;
-                       } else if (post_len > 0) {
+               pfd[TO_CGI].fd = toCgi_wr;
+               pfd[TO_CGI].events = POLLOUT;
+
+               if (toCgi_wr && hdr_cnt <= 0) {
+                       if (post_len > 0) {
+                               /* Expect more POST data from network */
+                               pfd[0].fd = 0;
                                pfd[0].events = POLLIN;
                        } else {
                                /* post_len <= 0 && hdr_cnt <= 0:
@@ -1127,7 +1132,7 @@ static NOINLINE void cgi_io_loop_and_exit(int fromCgi_rd, int toCgi_wr, int post
                }
 
                /* Now wait on the set of sockets */
-               count = safe_poll(pfd, toCgi_wr ? TO_CGI+1 : FROM_CGI+1, -1);
+               count = safe_poll(pfd, hdr_cnt > 0 ? TO_CGI+1 : FROM_CGI+1, -1);
                if (count <= 0) {
 #if 0
                        if (safe_waitpid(pid, &status, WNOHANG) <= 0) {
@@ -1144,7 +1149,7 @@ static NOINLINE void cgi_io_loop_and_exit(int fromCgi_rd, int toCgi_wr, int post
                }
 
                if (pfd[TO_CGI].revents) {
-                       /* hdr_cnt > 0 here due to the way pfd[TO_CGI].events set */
+                       /* hdr_cnt > 0 here due to the way poll() called */
                        /* Have data from peer and can write to CGI */
                        count = safe_write(toCgi_wr, hdr_ptr, hdr_cnt);
                        /* Doesn't happen, we dont use nonblocking IO here