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>

1 files changed, 13 insertions, 8 deletions

diff --git a/networking/httpd.c b/networking/httpd.c
index cef9b8baf..143331389 100644
--- 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