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f99cd56230
syzkaller report:
kernel BUG at net/core/skbuff.c:3452!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.7.0-rc4-00009-gbee0e7762ad2-dirty #135
RIP: 0010:skb_copy_and_csum_bits (net/core/skbuff.c:3452)
Call Trace:
icmp_glue_bits (net/ipv4/icmp.c:357)
__ip_append_data.isra.0 (net/ipv4/ip_output.c:1165)
ip_append_data (net/ipv4/ip_output.c:1362 net/ipv4/ip_output.c:1341)
icmp_push_reply (net/ipv4/icmp.c:370)
__icmp_send (./include/net/route.h:252 net/ipv4/icmp.c:772)
ip_fragment.constprop.0 (./include/linux/skbuff.h:1234 net/ipv4/ip_output.c:592 net/ipv4/ip_output.c:577)
__ip_finish_output (net/ipv4/ip_output.c:311 net/ipv4/ip_output.c:295)
ip_output (net/ipv4/ip_output.c:427)
__ip_queue_xmit (net/ipv4/ip_output.c:535)
__tcp_transmit_skb (net/ipv4/tcp_output.c:1462)
__tcp_retransmit_skb (net/ipv4/tcp_output.c:3387)
tcp_retransmit_skb (net/ipv4/tcp_output.c:3404)
tcp_retransmit_timer (net/ipv4/tcp_timer.c:604)
tcp_write_timer (./include/linux/spinlock.h:391 net/ipv4/tcp_timer.c:716)
The panic issue was trigered by tcp simultaneous initiation.
The initiation process is as follows:
TCP A TCP B
1. CLOSED CLOSED
2. SYN-SENT --> <SEQ=100><CTL=SYN> ...
3. SYN-RECEIVED <-- <SEQ=300><CTL=SYN> <-- SYN-SENT
4. ... <SEQ=100><CTL=SYN> --> SYN-RECEIVED
5. SYN-RECEIVED --> <SEQ=100><ACK=301><CTL=SYN,ACK> ...
// TCP B: not send challenge ack for ack limit or packet loss
// TCP A: close
tcp_close
tcp_send_fin
if (!tskb && tcp_under_memory_pressure(sk))
tskb = skb_rb_last(&sk->tcp_rtx_queue); //pick SYN_ACK packet
TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN; // set FIN flag
6. FIN_WAIT_1 --> <SEQ=100><ACK=301><END_SEQ=102><CTL=SYN,FIN,ACK> ...
// TCP B: send challenge ack to SYN_FIN_ACK
7. ... <SEQ=301><ACK=101><CTL=ACK> <-- SYN-RECEIVED //challenge ack
// TCP A: <SND.UNA=101>
8. FIN_WAIT_1 --> <SEQ=101><ACK=301><END_SEQ=102><CTL=SYN,FIN,ACK> ... // retransmit panic
__tcp_retransmit_skb //skb->len=0
tcp_trim_head
len = tp->snd_una - TCP_SKB_CB(skb)->seq // len=101-100
__pskb_trim_head
skb->data_len -= len // skb->len=-1, wrap around
... ...
ip_fragment
icmp_glue_bits //BUG_ON
If we use tcp_trim_head() to remove acked SYN from packet that contains data
or other flags, skb->len will be incorrectly decremented. We can remove SYN
flag that has been acked from rtx_queue earlier than tcp_trim_head(), which
can fix the problem mentioned above.
Fixes:
|
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.