CVE-2016-9919 (published 2016-12-08T17:59Z)

The icmp6_send function in net/ipv6/icmp.c in the Linux kernel through 4.8.12 omits a certain check of the dst data structure, which allows remote attackers to cause a denial of service (panic) via a fragmented IPv6 packet.

Severity: HIGH
CVSS v2 base score: 7.8 (AV:N/AC:L/Au:N/C:N/I:N/A:C)
CVSS v3 base score: 7.5, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-20
cwe_name: Improper Input Validation
description: The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.
extended_description: 
	   Input validation is a frequently-used technique
	   for checking potentially dangerous inputs in order to
	   ensure that the inputs are safe for processing within the
	   code, or when communicating with other components.  When
	   software does not validate input properly, an attacker is
	   able to craft the input in a form that is not expected by
	   the rest of the application. This will lead to parts of the
	   system receiving unintended input, which may result in
	   altered control flow, arbitrary control of a resource, or
	   arbitrary code execution.
	   Input validation is not the only technique for
	   processing input, however.  Other techniques attempt to
	   transform potentially-dangerous input into something safe, such
	   as filtering (CWE-790) - which attempts to remove dangerous
	   inputs - or encoding/escaping (CWE-116), which attempts to
	   ensure that the input is not misinterpreted when it is included
	   in output to another component. Other techniques exist as well
	   (see CWE-138 for more examples.)
	   Input validation can be applied to:
	   
	     raw data - strings, numbers, parameters, file contents, etc.
	     metadata - information about the raw data, such as headers or size
	   
	   Data can be simple or structured.  Structured data
	   can be composed of many nested layers, composed of
	   combinations of metadata and raw data, with other simple or
	   structured data.
	   Many properties of raw data or metadata may need
	   to be validated upon entry into the code, such
	   as:
	   
	     specified quantities such as size, length, frequency, price, rate, number of operations, time, etc.
	     implied or derived quantities, such as the actual size of a file instead of a specified size
	     indexes, offsets, or positions into more complex data structures
	     symbolic keys or other elements into hash tables, associative arrays, etc.
	     well-formedness, i.e. syntactic correctness - compliance with expected syntax 
	     lexical token correctness - compliance with rules for what is treated as a token
	     specified or derived type - the actual type of the input (or what the input appears to be)
	     consistency - between individual data elements, between raw data and metadata, between references, etc.
	     conformance to domain-specific rules, e.g. business logic 
	     equivalence - ensuring that equivalent inputs are treated the same
	     authenticity, ownership, or other attestations about the input, e.g. a cryptographic signature to prove the source of the data
	   
	   Implied or derived properties of data must often
	   be calculated or inferred by the code itself.  Errors in
	   deriving properties may be considered a contributing factor
	   to improper input validation.
	   
	   Note that "input validation" has very different
	   meanings to different people, or within different
	   classification schemes.  Caution must be used when
	   referencing this CWE entry or mapping to it.  For example,
	   some weaknesses might involve inadvertently giving control
	   to an attacker over an input when they should not be able
	   to provide an input at all, but sometimes this is referred
	   to as input validation.
	   Finally, it is important to emphasize that the
	   distinctions between input validation and output escaping
	   are often blurred, and developers must be careful to
	   understand the difference, including how input validation
	   is not always sufficient to prevent vulnerabilities,
	   especially when less stringent data types must be
	   supported, such as free-form text. Consider a SQL injection
	   scenario in which a person's last name is inserted into a
	   query. The name "O'Reilly" would likely pass the validation
	   step since it is a common last name in the English
	   language. However, this valid name cannot be directly
	   inserted into the database because it contains the "'"
	   apostrophe character, which would need to be escaped or
	   otherwise transformed. In this case, removing the
	   apostrophe might reduce the risk of SQL injection, but it
	   would produce incorrect behavior because the wrong name
	   would be recorded.
       
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: David Ahern
author_date: 2016-11-27 18:52:53-08:00
msg: net: handle no dst on skb in icmp6_send

Andrey reported the following while fuzzing the kernel with syzkaller:

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 0 PID: 3859 Comm: a.out Not tainted 4.9.0-rc6+ #429
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff8800666d4200 task.stack: ffff880067348000
RIP: 0010:[<ffffffff833617ec>]  [<ffffffff833617ec>]
icmp6_send+0x5fc/0x1e30 net/ipv6/icmp.c:451
RSP: 0018:ffff88006734f2c0  EFLAGS: 00010206
RAX: ffff8800666d4200 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: dffffc0000000000 RDI: 0000000000000018
RBP: ffff88006734f630 R08: ffff880064138418 R09: 0000000000000003
R10: dffffc0000000000 R11: 0000000000000005 R12: 0000000000000000
R13: ffffffff84e7e200 R14: ffff880064138484 R15: ffff8800641383c0
FS:  00007fb3887a07c0(0000) GS:ffff88006cc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 000000006b040000 CR4: 00000000000006f0
Stack:
 ffff8800666d4200 ffff8800666d49f8 ffff8800666d4200 ffffffff84c02460
 ffff8800666d4a1a 1ffff1000ccdaa2f ffff88006734f498 0000000000000046
 ffff88006734f440 ffffffff832f4269 ffff880064ba7456 0000000000000000
Call Trace:
 [<ffffffff83364ddc>] icmpv6_param_prob+0x2c/0x40 net/ipv6/icmp.c:557
 [<     inline     >] ip6_tlvopt_unknown net/ipv6/exthdrs.c:88
 [<ffffffff83394405>] ip6_parse_tlv+0x555/0x670 net/ipv6/exthdrs.c:157
 [<ffffffff8339a759>] ipv6_parse_hopopts+0x199/0x460 net/ipv6/exthdrs.c:663
 [<ffffffff832ee773>] ipv6_rcv+0xfa3/0x1dc0 net/ipv6/ip6_input.c:191
 ...

icmp6_send / icmpv6_send is invoked for both rx and tx paths. In both
cases the dst->dev should be preferred for determining the L3 domain
if the dst has been set on the skb. Fallback to the skb->dev if it has
not. This covers the case reported here where icmp6_send is invoked on
Rx before the route lookup.

Fixes: 5d41ce29e ("net: icmp6_send should use dst dev to determine L3 domain")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: icmp.c
change_type: ModificationType.MODIFY
diff: @@ -447,8 +447,10 @@ static void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
 
 	if (__ipv6_addr_needs_scope_id(addr_type))
 		iif = skb->dev->ifindex;
-	else
-		iif = l3mdev_master_ifindex(skb_dst(skb)->dev);
+	else {
+		dst = skb_dst(skb);
+		iif = l3mdev_master_ifindex(dst ? dst->dev : skb->dev);
+	}
 
 	/*
 	 *	Must not send error if the source does not uniquely

programming_language: C