Messages in this thread | | | Subject | Re: [syzbot] WARNING in xfrm_alloc_compat (2) | From | Dmitry Safonov <> | Date | Mon, 29 Mar 2021 21:42:07 +0100 |
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On 3/29/21 9:31 PM, Eric Dumazet wrote: > > > On 3/29/21 9:57 PM, Dmitry Safonov wrote: [..] >>> ------------[ cut here ]------------ >>> unsupported nla_type 356 >> >> This doesn't seem to be an issue. >> Userspace sent message with nla_type 356, which is > __XFRM_MSG_MAX, so >> this warning is expected. I've added it so when a new XFRM_MSG_* will be >> added, to make sure that there will be translations to such messages in >> xfrm_compat.ko (if the translation needed). >> This is WARN_ON_ONCE(), so it can't be used as DOS. >> >> Ping me if you'd expect something else than once-a-boot warning for >> this. Not sure how-to close syzkaller bug, docs have only `invalid' tag, >> which isn't `not-a-bug'/`expected' tag: >> https://github.com/google/syzkaller/blob/master/docs/syzbot.md >> > > You should not use WARN_ON_ONCE() for this case (if user space can trigger it) > > https://lwn.net/Articles/769365/ > > <quote> > Greg Kroah-Hartman raised the problem of core kernel API code that will use WARN_ON_ONCE() to complain about bad usage; that will not generate the desired result if WARN_ON_ONCE() is configured to crash the machine. He was told that the code should just call pr_warn() instead, and that the called function should return an error in such situations. It was generally agreed that any WARN_ON() or WARN_ON_ONCE() calls that can be triggered from user space need to be fixed. > </quote>
Yeah, fair enough, I've already thought after sending the reply that WARN_ON*() prints registers and that may be unwanted. I'll cook a patch to convert this and other WARNs in the module.
I wish there was something like pr_warn_backtrace_once(), but I guess it's fine without dumpstack(), after all.
Thanks, Dmitry
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