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Subject[PATCH 5.4 30/33] tipc: fix NULL deref in tipc_link_xmit()
Date
From: Hoang Le <hoang.h.le@dektech.com.au>

[ Upstream commit b77413446408fdd256599daf00d5be72b5f3e7c6 ]

The buffer list can have zero skb as following path:
tipc_named_node_up()->tipc_node_xmit()->tipc_link_xmit(), so
we need to check the list before casting an &sk_buff.

Fault report:
[] tipc: Bulk publication failure
[] general protection fault, probably for non-canonical [#1] PREEMPT [...]
[] KASAN: null-ptr-deref in range [0x00000000000000c8-0x00000000000000cf]
[] CPU: 0 PID: 0 Comm: swapper/0 Kdump: loaded Not tainted 5.10.0-rc4+ #2
[] Hardware name: Bochs ..., BIOS Bochs 01/01/2011
[] RIP: 0010:tipc_link_xmit+0xc1/0x2180
[] Code: 24 b8 00 00 00 00 4d 39 ec 4c 0f 44 e8 e8 d7 0a 10 f9 48 [...]
[] RSP: 0018:ffffc90000006ea0 EFLAGS: 00010202
[] RAX: dffffc0000000000 RBX: ffff8880224da000 RCX: 1ffff11003d3cc0d
[] RDX: 0000000000000019 RSI: ffffffff886007b9 RDI: 00000000000000c8
[] RBP: ffffc90000007018 R08: 0000000000000001 R09: fffff52000000ded
[] R10: 0000000000000003 R11: fffff52000000dec R12: ffffc90000007148
[] R13: 0000000000000000 R14: 0000000000000000 R15: ffffc90000007018
[] FS: 0000000000000000(0000) GS:ffff888037400000(0000) knlGS:000[...]
[] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[] CR2: 00007fffd2db5000 CR3: 000000002b08f000 CR4: 00000000000006f0

Fixes: af9b028e270fd ("tipc: make media xmit call outside node spinlock context")
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Hoang Le <hoang.h.le@dektech.com.au>
Link: https://lore.kernel.org/r/20210108071337.3598-1-hoang.h.le@dektech.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/tipc/link.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -939,9 +939,7 @@ void tipc_link_reset(struct tipc_link *l
int tipc_link_xmit(struct tipc_link *l, struct sk_buff_head *list,
struct sk_buff_head *xmitq)
{
- struct tipc_msg *hdr = buf_msg(skb_peek(list));
unsigned int maxwin = l->window;
- int imp = msg_importance(hdr);
unsigned int mtu = l->mtu;
u16 ack = l->rcv_nxt - 1;
u16 seqno = l->snd_nxt;
@@ -950,8 +948,14 @@ int tipc_link_xmit(struct tipc_link *l,
struct sk_buff_head *backlogq = &l->backlogq;
struct sk_buff *skb, *_skb, **tskb;
int pkt_cnt = skb_queue_len(list);
+ struct tipc_msg *hdr;
int rc = 0;
+ int imp;

+ if (pkt_cnt <= 0)
+ return 0;
+
+ hdr = buf_msg(skb_peek(list));
if (unlikely(msg_size(hdr) > mtu)) {
pr_warn("Too large msg, purging xmit list %d %d %d %d %d!\n",
skb_queue_len(list), msg_user(hdr),
@@ -960,6 +964,7 @@ int tipc_link_xmit(struct tipc_link *l,
return -EMSGSIZE;
}

+ imp = msg_importance(hdr);
/* Allow oversubscription of one data msg per source at congestion */
if (unlikely(l->backlog[imp].len >= l->backlog[imp].limit)) {
if (imp == TIPC_SYSTEM_IMPORTANCE) {

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