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Herbert Xu 2a0a6ebee1 [NETLINK]: Synchronous message processing. ... Let's recap the problem. The current asynchronous netlink kernel message processing is vulnerable to these attacks: 1) Hit and run: Attacker sends one or more messages and then exits before they're processed. This may confuse/disable the next netlink user that gets the netlink address of the attacker since it may receive the responses to the attacker's messages. Proposed solutions: a) Synchronous processing. b) Stream mode socket. c) Restrict/prohibit binding. 2) Starvation: Because various netlink rcv functions were written to not return until all messages have been processed on a socket, it is possible for these functions to execute for an arbitrarily long period of time. If this is successfully exploited it could also be used to hold rtnl forever. Proposed solutions: a) Synchronous processing. b) Stream mode socket. Firstly let's cross off solution c). It only solves the first problem and it has user-visible impacts. In particular, it'll break user space applications that expect to bind or communicate with specific netlink addresses (pid's). So we're left with a choice of synchronous processing versus SOCK_STREAM for netlink. For the moment I'm sticking with the synchronous approach as suggested by Alexey since it's simpler and I'd rather spend my time working on other things. However, it does have a number of deficiencies compared to the stream mode solution: 1) User-space to user-space netlink communication is still vulnerable. 2) Inefficient use of resources. This is especially true for rtnetlink since the lock is shared with other users such as networking drivers. The latter could hold the rtnl while communicating with hardware which causes the rtnetlink user to wait when it could be doing other things. 3) It is still possible to DoS all netlink users by flooding the kernel netlink receive queue. The attacker simply fills the receive socket with a single netlink message that fills up the entire queue. The attacker then continues to call sendmsg with the same message in a loop. Point 3) can be countered by retransmissions in user-space code, however it is pretty messy. In light of these problems (in particular, point 3), we should implement stream mode netlink at some point. In the mean time, here is a patch that implements synchronous processing. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>		20 years ago
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irq	…
power	[PATCH] DocBook: changes and extensions to the kernel documentation	20 years ago
Makefile	…
acct.c	…
audit.c	[NETLINK]: Synchronous message processing.	20 years ago
auditsc.c	…
capability.c	…
compat.c	…
configs.c	…
cpu.c	…
cpuset.c	…
dma.c	…
exec_domain.c	…
exit.c	[PATCH] make lots of things static	20 years ago
extable.c	…
fork.c	…
futex.c	[PATCH] convert that currently tests _NSIG directly to use valid_signal()	20 years ago
intermodule.c	…
itimer.c	…
kallsyms.c	…
kfifo.c	…
kmod.c	…
kprobes.c	…
ksysfs.c	…
kthread.c	…
module.c	[PATCH] Change synchronize_kernel to _rcu and _sched	20 years ago
panic.c	…
params.c	…
pid.c	…
posix-cpu-timers.c	…
posix-timers.c	…
printk.c	…
profile.c	[PATCH] Change synchronize_kernel to _rcu and _sched	20 years ago
ptrace.c	[PATCH] convert that currently tests _NSIG directly to use valid_signal()	20 years ago
rcupdate.c	…
resource.c	…
sched.c	[PATCH] DocBook: fix some descriptions	20 years ago
seccomp.c	…
signal.c	[PATCH] convert that currently tests _NSIG directly to use valid_signal()	20 years ago
softirq.c	…
spinlock.c	…
stop_machine.c	…
sys.c	[PATCH] convert that currently tests _NSIG directly to use valid_signal()	20 years ago
sys_ni.c	[PATCH] consolidate sys_shmat	20 years ago
sysctl.c	[PATCH] DocBook: fix some descriptions	20 years ago
time.c	…
timer.c	…
uid16.c	…
user.c	…
wait.c	…
workqueue.c	…