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[Qemu-devel] [PATCH 1/3] char: fix vhost-user socket full


From: Didier Pallard
Subject: [Qemu-devel] [PATCH 1/3] char: fix vhost-user socket full
Date: Thu, 3 Dec 2015 10:53:17 +0100

unix_send_msgfds is used by vhost-user control socket. qemu_chr_fe_write_all
is used to send a message and retries as long as EAGAIN errno is set,
but write_msgfds buffer is freed after first EAGAIN failure, causing
message to be sent without proper fds attachment.

In case unix_send_msgfds is called through qemu_chr_fe_write, it will be
user responsability to resend message as is or to free write_msgfds
using set_msgfds(0)

Signed-off-by: Didier Pallard <address@hidden>
Reviewed-by: Thibaut Collet <address@hidden>
---
 qemu-char.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/qemu-char.c b/qemu-char.c
index 5448b0f..26d5f2e 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2614,6 +2614,16 @@ static int unix_send_msgfds(CharDriverState *chr, const 
uint8_t *buf, int len)
         r = sendmsg(s->fd, &msgh, 0);
     } while (r < 0 && errno == EINTR);
 
+    /* Ancillary data are not sent if no byte is written
+     * so don't free msgfds buffer if return value is EAGAIN
+     * If called from qemu_chr_fe_write_all retry will come soon
+     * If called from qemu_chr_fe_write, it is the user responsibility
+     * to resend message or free fds using set_msgfds(0)
+     */
+    if (r < 0 && errno == EAGAIN) {
+        return r;
+    }
+
     /* free the written msgfds, no matter what */
     if (s->write_msgfds_num) {
         g_free(s->write_msgfds);
-- 
2.1.4




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