Kernel v4.19-rc4 KASAN complaint

[hch@infradead.org (Christoph Hellwig)]

[Adding Paul]

Hi Paul,

Bart reported a use after free in the SRCU code when testing the
nvme multipath code here:

http://lists.infradead.org/pipermail/linux-nvme/2018-September/020009.html

Based on his analsys it appears to me the use after free is on the
srcu_data structure, which is internal to the SRCU implementation.

While I don't want to exclude an actual cause in the nvme code I wonder
if you have any additional insights from the RCU perspective.

On Thu, Sep 20, 2018@10:24:01AM -0700, Bart Van Assche wrote:
> On Thu, 2018-09-20@00:10 -0700, Christoph Hellwig wrote:
> > On Tue, Sep 18, 2018@02:16:48PM -0700, Bart Van Assche wrote:
> > > Hello,
> > > 
> > > If I run the nvmeof-mp tests from https://github.com/bvanassche/blktests
> > > against kernel v4.19-rc4 then a KASAN complaint appears. This complaint does
> > > not appear when I run these tests against kernel v4.18. Could this be a
> > > regression?
> > 
> > Sounds like it is.  4.19 has the new ANA code, so the multipath code
> > has some churn.
> > 
> > > BUG: KASAN: use-after-free in srcu_invoke_callbacks+0x207/0x290
> > 
> > Can you resolve the address using gdb on vmlinux to a specific
> > line of code?
> 
> Sure. The gdb output (which is probably not very useful) is as follows:
> 
> (gdb) list *(srcu_invoke_callbacks+0x207)
> 0xffffffff811872e7 is in srcu_invoke_callbacks (./include/linux/compiler.h:188).
> 183     })
> 184
> 185     static __always_inline
> 186     void __read_once_size(const volatile void *p, void *res, int size)
> 187     {
> 188             __READ_ONCE_SIZE;
> 189     }
> 190
> 191     #ifdef CONFIG_KASAN
> 192     /*
> 
> This may be more useful:
> 
> (gdb) list *(srcu_invoke_callbacks+0x1fa)
> 0xffffffff811872da is in srcu_invoke_callbacks (kernel/rcu/srcutree.c:1206).
> 1201            /*
> 1202             * Update counts, accelerate new callbacks, and if needed,
> 1203             * schedule another round of callback invocation.
> 1204             */
> 1205            spin_lock_irq_rcu_node(sdp);
> 1206            rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
> 1207            (void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
> 1208                                           rcu_seq_snap(&sp->srcu_gp_seq));
> 1209            sdp->srcu_cblist_invoking = false;
> 1210            more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
> 
> Bart.
> 
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