[Qemu-devel] [PATCH 2/2] slirp: Fix packet expiration

[Jan Kiszka]

From: Thomas Huth <address@hidden>

The two new variables "arp_requested" and "expiration_date" in the mbuf
structure have been added after the variable-sized "m_dat_" array. The
variables have to be added before the m_dat_ array instead.
Without this patch, the expiration_date gets clobbered by code that
accesses the m_dat_ array.
I experienced this problem with the code in slirp/tftp.c: The
tftp_send_data() function created a new packet with the m_get()
function (which fills-in a default expiration_date value). Then the
TFTP code cleared the data section of the packet, which accidentially
also cleared the expiration_date. This zeroed expiration_date then
finally causes the packet to be discarded during if_start(), so that
TFTP packets were not transmitted anymore.

[Jan: added comment as suggested by Fabien ]

CC: Fabien Chouteau <address@hidden>
Signed-off-by: Thomas Huth <address@hidden>
Signed-off-by: Jan Kiszka <address@hidden>
---
 slirp/mbuf.h |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/slirp/mbuf.h b/slirp/mbuf.h
index 55170e5..0708840 100644
--- a/slirp/mbuf.h
+++ b/slirp/mbuf.h
@@ -82,12 +82,13 @@ struct m_hdr {
 struct mbuf {
        struct  m_hdr m_hdr;
        Slirp *slirp;
+       bool    arp_requested;
+       uint64_t expiration_date;
+       /* start of dynamic buffer area, must be last element */
        union M_dat {
                char    m_dat_[1]; /* ANSI don't like 0 sized arrays */
                char    *m_ext_;
        } M_dat;
-    bool     arp_requested;
-    uint64_t expiration_date;
 };
 
 #define m_next         m_hdr.mh_next
-- 
1.7.3.4