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| H A D | ipmr.c | diff 7901cd97963d6cbde88fa25a4a446db3554c16c6 Fri Nov 15 18:29:52 CET 2019 Guillaume Nault <gnault@redhat.com> ipmr: Fix skb headroom in ipmr_get_route().
In route.c, inet_rtm_getroute_build_skb() creates an skb with no
headroom. This skb is then used by inet_rtm_getroute() which may pass
it to rt_fill_info() and, from there, to ipmr_get_route(). The later
might try to reuse this skb by cloning it and prepending an IPv4
header. But since the original skb has no headroom, skb_push() triggers
skb_under_panic():
skbuff: skb_under_panic: text:00000000ca46ad8a len:80 put:20 head:00000000cd28494e data:000000009366fd6b tail:0x3c end:0xec0 dev:veth0
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:108!
invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 6 PID: 587 Comm: ip Not tainted 5.4.0-rc6+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014
RIP: 0010:skb_panic+0xbf/0xd0
Code: 41 a2 ff 8b 4b 70 4c 8b 4d d0 48 c7 c7 20 76 f5 8b 44 8b 45 bc 48 8b 55 c0 48 8b 75 c8 41 54 41 57 41 56 41 55 e8 75 dc 7a ff <0f> 0b 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00
RSP: 0018:ffff888059ddf0b0 EFLAGS: 00010286
RAX: 0000000000000086 RBX: ffff888060a315c0 RCX: ffffffff8abe4822
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff88806c9a79cc
RBP: ffff888059ddf118 R08: ffffed100d9361b1 R09: ffffed100d9361b0
R10: ffff88805c68aee3 R11: ffffed100d9361b1 R12: ffff88805d218000
R13: ffff88805c689fec R14: 000000000000003c R15: 0000000000000ec0
FS: 00007f6af184b700(0000) GS:ffff88806c980000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc8204a000 CR3: 0000000057b40006 CR4: 0000000000360ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
skb_push+0x7e/0x80
ipmr_get_route+0x459/0x6fa
rt_fill_info+0x692/0x9f0
inet_rtm_getroute+0xd26/0xf20
rtnetlink_rcv_msg+0x45d/0x630
netlink_rcv_skb+0x1a5/0x220
rtnetlink_rcv+0x15/0x20
netlink_unicast+0x305/0x3a0
netlink_sendmsg+0x575/0x730
sock_sendmsg+0xb5/0xc0
___sys_sendmsg+0x497/0x4f0
__sys_sendmsg+0xcb/0x150
__x64_sys_sendmsg+0x48/0x50
do_syscall_64+0xd2/0xac0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Actually the original skb used to have enough headroom, but the
reserve_skb() call was lost with the introduction of
inet_rtm_getroute_build_skb() by commit 404eb77ea766 ("ipv4: support
sport, dport and ip_proto in RTM_GETROUTE").
We could reserve some headroom again in inet_rtm_getroute_build_skb(),
but this function shouldn't be responsible for handling the special
case of ipmr_get_route(). Let's handle that directly in
ipmr_get_route() by calling skb_realloc_headroom() instead of
skb_clone().
Fixes: 404eb77ea766 ("ipv4: support sport, dport and ip_proto in RTM_GETROUTE")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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