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Message-ID: <8c853c0c-84f0-c8be-3020-561db6f87081@huawei.com>
Date: Wed, 16 Aug 2023 12:27:20 +0800
From: Zheng Yejian <zhengyejian1@...wei.com>
To: <rostedt@...dmis.org>, <mhiramat@...nel.org>
CC: <fweisbec@...il.com>, <linux-kernel@...r.kernel.org>,
<linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Fix memleak due to race between current_tracer
and trace
On 2023/8/16 09:45, Zheng Yejian wrote:
> On 2023/8/8 17:29, Zheng Yejian wrote:
>> Kmemleak report a leak in graph_trace_open():
>>
>> unreferenced object 0xffff0040b95f4a00 (size 128):
>> comm "cat", pid 204981, jiffies 4301155872 (age 99771.964s)
>> hex dump (first 32 bytes):
>> e0 05 e7 b4 ab 7d 00 00 0b 00 01 00 00 00 00 00 .....}..........
>> f4 00 01 10 00 a0 ff ff 00 00 00 00 65 00 10 00 ............e...
>> backtrace:
>> [<000000005db27c8b>] kmem_cache_alloc_trace+0x348/0x5f0
>> [<000000007df90faa>] graph_trace_open+0xb0/0x344
>> [<00000000737524cd>] __tracing_open+0x450/0xb10
>> [<0000000098043327>] tracing_open+0x1a0/0x2a0
>> [<00000000291c3876>] do_dentry_open+0x3c0/0xdc0
>> [<000000004015bcd6>] vfs_open+0x98/0xd0
>> [<000000002b5f60c9>] do_open+0x520/0x8d0
>> [<00000000376c7820>] path_openat+0x1c0/0x3e0
>> [<00000000336a54b5>] do_filp_open+0x14c/0x324
>> [<000000002802df13>] do_sys_openat2+0x2c4/0x530
>> [<0000000094eea458>] __arm64_sys_openat+0x130/0x1c4
>> [<00000000a71d7881>] el0_svc_common.constprop.0+0xfc/0x394
>> [<00000000313647bf>] do_el0_svc+0xac/0xec
>> [<000000002ef1c651>] el0_svc+0x20/0x30
>> [<000000002fd4692a>] el0_sync_handler+0xb0/0xb4
>> [<000000000c309c35>] el0_sync+0x160/0x180
>>
>> The root cause is descripted as follows:
>>
>> __tracing_open() { // 1. File 'trace' is being opened;
>> ...
>> *iter->trace = *tr->current_trace; // 2. Tracer 'function_graph' is
>> // currently set;
>> ...
>> iter->trace->open(iter); // 3. Call graph_trace_open() here,
>> // and memory are allocated in it;
>> ...
>> }
>>
>> s_start() { // 4. The opened file is being read;
>> ...
>> *iter->trace = *tr->current_trace; // 5. If tracer is switched to
>> // 'nop' or others, then
>> memory
>> // in step 3 are leaked!!!
>> ...
>> }
>>
>> To fix it, in s_start(), close tracer before switching then reopen the
>> new tracer after switching.
>>
>> Fixes: d7350c3f4569 ("tracing/core: make the read callbacks reentrants")
>> Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
>> ---
>> kernel/trace/trace.c | 9 ++++++++-
>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index b8870078ef58..d50a0227baa3 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -4213,8 +4213,15 @@ static void *s_start(struct seq_file *m, loff_t
>> *pos)
>> * will point to the same string as current_trace->name.
>> */
>> mutex_lock(&trace_types_lock);
>> - if (unlikely(tr->current_trace && iter->trace->name !=
>> tr->current_trace->name))
>> + if (unlikely(tr->current_trace && iter->trace->name !=
>> tr->current_trace->name)) {
>> + /* Close iter->trace before switching to the new current
>> tracer */
>> + if (iter->trace->close)
>> + iter->trace->close(iter);
>
> Hi, kasan report an issue related to this patch in v5.10, I'll handle
> it and then send V2 if the patch needs to be changed.
>
> BUG: KASAN: use-after-free in graph_trace_close+0x78/0x7c
> Read of size 8 at addr ffff204054ca8f00 by task cat/193541
> [...]
> Call trace:
> dump_backtrace+0x0/0x3e4
> show_stack+0x20/0x2c
> dump_stack+0x140/0x198
> print_address_description.constprop.0+0x2c/0x1fc
> __kasan_report+0xe0/0x140
> kasan_report+0x44/0x5c
> __asan_report_load8_noabort+0x34/0x60
> graph_trace_close+0x78/0x7c
> wakeup_trace_close+0x3c/0x54
> s_start+0x4f4/0x794
> seq_read_iter+0x210/0xd90
> seq_read+0x288/0x410
> vfs_read+0x13c/0x41c
> ksys_read+0xf4/0x1e0
> __arm64_sys_read+0x74/0xa4
> el0_svc_common.constprop.0+0xfc/0x394
> do_el0_svc+0xac/0xec
> el0_svc+0x20/0x30
> el0_sync_handler+0xb0/0xb4
> el0_sync+0x160/0x180
>
> Allocated by task 193541:
> kasan_save_stack+0x28/0x60
> __kasan_kmalloc.constprop.0+0xa4/0xd0
> kasan_kmalloc+0x10/0x20
> kmem_cache_alloc_trace+0x2ec/0x5f0
> graph_trace_open+0xb0/0x344
> __tracing_open+0x450/0xb10
> tracing_open+0x1a0/0x2a0
> do_dentry_open+0x3c0/0xdc0
> vfs_open+0x98/0xd0
> do_open+0x520/0x8d0
>
The root cause should be that:
1. As __tracing_open() being called, function graph tracer is set,
then graph_trace_open() is called;
2. As s_start() being called, switch to wakeup tracer, then
graph_trace_close() is called, here 'iter->private' is not cleared.
Then wakeup_trace_open() is called, and if graph_trace_open() is
not called by it due to is_graph(iter->tr) returns false;
3. As next time s_start() being called, if tracer switched again then
wakeup_trace_close() is called and it mistakenly close the
'iter->private' in step 2 which finally causes kasan do the report.
So we may also need to set 'iter->private' to be NULL in
graph_trace_close(), I'll send v2 soon.
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -1244,6 +1244,7 @@ void graph_trace_close(struct trace_iterator *iter)
if (data) {
free_percpu(data->cpu_data);
kfree(data);
+ iter->private = NULL;
}
}
-- Zheng Yejian
>> *iter->trace = *tr->current_trace;
>> + /* Reopen the new current tracer */
>> + if (iter->trace->open)
>> + iter->trace->open(iter);
>> + }
>> mutex_unlock(&trace_types_lock);
>> #ifdef CONFIG_TRACER_MAX_TRACE
>
>
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