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[libvirt] [PATCH] Remove & ban use of select() for waiting for I/O



From: "Daniel P. Berrange" <berrange redhat com>

Use of the select() system call is inherantly dangerous since
applications will hit a buffer overrun if any FD number exceeds
the size of the select set size (typically 1024). Replace the
two uses of select() with poll() and use cfg.mk to ban any
future use of select().

NB: This changes the phyp driver so that it uses an infinite
timeout, instead of busy-waiting for 1ms at a time.

Signed-off-by: Daniel P. Berrange <berrange redhat com>
---
 cfg.mk                 |  8 ++++++++
 src/phyp/phyp_driver.c | 20 +++++++-------------
 src/util/virnetlink.c  | 16 +++++++---------
 3 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/cfg.mk b/cfg.mk
index 0bf5bfc..0e809fc 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -444,6 +444,14 @@ sc_prohibit_nonreentrant:
 	done ; \
 	exit $$fail
 
+sc_prohibit_select:
+	@fail=0 ;							\
+	(prohibit="\\<select *\\("					\
+	 halt="use poll(), not select()"				\
+	 $(_sc_search_regexp)						\
+	) || fail=1;							\
+	exit $$fail
+
 # Prohibit the inclusion of <ctype.h>.
 sc_prohibit_ctype_h:
 	@prohibit='^# *include  *<ctype\.h>'				\
diff --git a/src/phyp/phyp_driver.c b/src/phyp/phyp_driver.c
index f0007c0..4594cbf 100644
--- a/src/phyp/phyp_driver.c
+++ b/src/phyp/phyp_driver.c
@@ -40,6 +40,7 @@
 #include <netdb.h>
 #include <fcntl.h>
 #include <domain_event.h>
+#include <poll.h>
 
 #include "internal.h"
 #include "virauth.h"
@@ -72,29 +73,22 @@ static unsigned const int PHYP_MAC_SIZE= 12;
 static int
 waitsocket(int socket_fd, LIBSSH2_SESSION * session)
 {
-    struct timeval timeout;
-    fd_set fd;
-    fd_set *writefd = NULL;
-    fd_set *readfd = NULL;
+    struct pollfd fds[1];
     int dir;
 
-    timeout.tv_sec = 0;
-    timeout.tv_usec = 1000;
-
-    FD_ZERO(&fd);
-
-    FD_SET(socket_fd, &fd);
+    memset(fds, 0, sizeof(fds));
+    fds[0].fd = socket_fd;
 
     /* now make sure we wait in the correct direction */
     dir = libssh2_session_block_directions(session);
 
     if (dir & LIBSSH2_SESSION_BLOCK_INBOUND)
-        readfd = &fd;
+        fds[0].events |= POLLIN;
 
     if (dir & LIBSSH2_SESSION_BLOCK_OUTBOUND)
-        writefd = &fd;
+        fds[0].events |= POLLOUT;
 
-    return select(socket_fd + 1, readfd, writefd, NULL, &timeout);
+    return poll(fds, ARRAY_CARDINALITY(fds), -1);
 }
 
 /* this function is the layer that manipulates the ssh channel itself
diff --git a/src/util/virnetlink.c b/src/util/virnetlink.c
index d340eda..f5865a0 100644
--- a/src/util/virnetlink.c
+++ b/src/util/virnetlink.c
@@ -48,7 +48,7 @@
 
 #define VIR_FROM_THIS VIR_FROM_NET
 
-#define NETLINK_ACK_TIMEOUT_S  2
+#define NETLINK_ACK_TIMEOUT_S  2*1000
 
 #if defined(__linux__) && defined(HAVE_LIBNL)
 /* State for a single netlink event handle */
@@ -185,10 +185,7 @@ int virNetlinkCommand(struct nl_msg *nl_msg,
             .nl_groups = 0,
     };
     ssize_t nbytes;
-    struct timeval tv = {
-        .tv_sec = NETLINK_ACK_TIMEOUT_S,
-    };
-    fd_set readfds;
+    struct pollfd fds[1];
     int fd;
     int n;
     struct nlmsghdr *nlmsg = nlmsg_hdr(nl_msg);
@@ -242,14 +239,15 @@ int virNetlinkCommand(struct nl_msg *nl_msg,
         goto error;
     }
 
-    FD_ZERO(&readfds);
-    FD_SET(fd, &readfds);
+    memset(fds, 0, sizeof(fds));
+    fds[0].fd = fd;
+    fds[0].events = POLLIN;
 
-    n = select(fd + 1, &readfds, NULL, NULL, &tv);
+    n = poll(fds, ARRAY_CARDINALITY(fds), NETLINK_ACK_TIMEOUT_S);
     if (n <= 0) {
         if (n < 0)
             virReportSystemError(errno, "%s",
-                                 _("error in select call"));
+                                 _("error in poll call"));
         if (n == 0)
             virReportSystemError(ETIMEDOUT, "%s",
                                  _("no valid netlink response was received"));
-- 
1.8.2.1


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