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Subject[PATCH net-next] fix unsafe set_memory_rw from softirq
Date
on x86 system with net.core.bpf_jit_enable = 1

sudo tcpdump -i eth1 'tcp port 22'

causes the warning:
[ 56.766097] Possible unsafe locking scenario:
[ 56.766097]
[ 56.780146] CPU0
[ 56.786807] ----
[ 56.793188] lock(&(&vb->lock)->rlock);
[ 56.799593] <Interrupt>
[ 56.805889] lock(&(&vb->lock)->rlock);
[ 56.812266]
[ 56.812266] *** DEADLOCK ***
[ 56.812266]
[ 56.830670] 1 lock held by ksoftirqd/1/13:
[ 56.836838] #0: (rcu_read_lock){.+.+..}, at: [<ffffffff8118f44c>] vm_unmap_aliases+0x8c/0x380
[ 56.849757]
[ 56.849757] stack backtrace:
[ 56.862194] CPU: 1 PID: 13 Comm: ksoftirqd/1 Not tainted 3.12.0-rc3+ #45
[ 56.868721] Hardware name: System manufacturer System Product Name/P8Z77 WS, BIOS 3007 07/26/2012
[ 56.882004] ffffffff821944c0 ffff88080bbdb8c8 ffffffff8175a145 0000000000000007
[ 56.895630] ffff88080bbd5f40 ffff88080bbdb928 ffffffff81755b14 0000000000000001
[ 56.909313] ffff880800000001 ffff880800000000 ffffffff8101178f 0000000000000001
[ 56.923006] Call Trace:
[ 56.929532] [<ffffffff8175a145>] dump_stack+0x55/0x76
[ 56.936067] [<ffffffff81755b14>] print_usage_bug+0x1f7/0x208
[ 56.942445] [<ffffffff8101178f>] ? save_stack_trace+0x2f/0x50
[ 56.948932] [<ffffffff810cc0a0>] ? check_usage_backwards+0x150/0x150
[ 56.955470] [<ffffffff810ccb52>] mark_lock+0x282/0x2c0
[ 56.961945] [<ffffffff810ccfed>] __lock_acquire+0x45d/0x1d50
[ 56.968474] [<ffffffff810cce6e>] ? __lock_acquire+0x2de/0x1d50
[ 56.975140] [<ffffffff81393bf5>] ? cpumask_next_and+0x55/0x90
[ 56.981942] [<ffffffff810cef72>] lock_acquire+0x92/0x1d0
[ 56.988745] [<ffffffff8118f52a>] ? vm_unmap_aliases+0x16a/0x380
[ 56.995619] [<ffffffff817628f1>] _raw_spin_lock+0x41/0x50
[ 57.002493] [<ffffffff8118f52a>] ? vm_unmap_aliases+0x16a/0x380
[ 57.009447] [<ffffffff8118f52a>] vm_unmap_aliases+0x16a/0x380
[ 57.016477] [<ffffffff8118f44c>] ? vm_unmap_aliases+0x8c/0x380
[ 57.023607] [<ffffffff810436b0>] change_page_attr_set_clr+0xc0/0x460
[ 57.030818] [<ffffffff810cfb8d>] ? trace_hardirqs_on+0xd/0x10
[ 57.037896] [<ffffffff811a8330>] ? kmem_cache_free+0xb0/0x2b0
[ 57.044789] [<ffffffff811b59c3>] ? free_object_rcu+0x93/0xa0
[ 57.051720] [<ffffffff81043d9f>] set_memory_rw+0x2f/0x40
[ 57.058727] [<ffffffff8104e17c>] bpf_jit_free+0x2c/0x40
[ 57.065577] [<ffffffff81642cba>] sk_filter_release_rcu+0x1a/0x30
[ 57.072338] [<ffffffff811108e2>] rcu_process_callbacks+0x202/0x7c0
[ 57.078962] [<ffffffff81057f17>] __do_softirq+0xf7/0x3f0
[ 57.085373] [<ffffffff81058245>] run_ksoftirqd+0x35/0x70

cannot reuse filter memory, since it's readonly, so have to
extend sk_filter with work_struct

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
arch/x86/net/bpf_jit_comp.c | 17 ++++++++++++-----
include/linux/filter.h | 1 +
2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 79c216a..89a43df 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -772,13 +772,20 @@ out:
return;
}

+static void bpf_jit_free_deferred(struct work_struct *work)
+{
+ struct sk_filter *fp = container_of(work, struct sk_filter, work);
+ unsigned long addr = (unsigned long)fp->bpf_func & PAGE_MASK;
+ struct bpf_binary_header *header = (void *)addr;
+
+ set_memory_rw(addr, header->pages);
+ module_free(NULL, header);
+}
+
void bpf_jit_free(struct sk_filter *fp)
{
if (fp->bpf_func != sk_run_filter) {
- unsigned long addr = (unsigned long)fp->bpf_func & PAGE_MASK;
- struct bpf_binary_header *header = (void *)addr;
-
- set_memory_rw(addr, header->pages);
- module_free(NULL, header);
+ INIT_WORK(&fp->work, bpf_jit_free_deferred);
+ schedule_work(&fp->work);
}
}
diff --git a/include/linux/filter.h b/include/linux/filter.h
index a6ac848..378fa03 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -27,6 +27,7 @@ struct sk_filter
unsigned int len; /* Number of filter blocks */
unsigned int (*bpf_func)(const struct sk_buff *skb,
const struct sock_filter *filter);
+ struct work_struct work;
struct rcu_head rcu;
struct sock_filter insns[0];
};
--
1.7.9.5


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