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Subject[PATCH v3] perf top: expand the range of multithreaded phase
Date
In __cmd_top, perf_set_multithreaded is used to enable pthread_rwlock, thus
donw_read and down_write can work to handle concurrency problems. Then top
use perf_set_singlethreaded and switch to single threaded phase, assuming
that no thread concurrency will happen later.
However, a UAF problem could occur in perf top in single threaded phase,
The concurrent procedure is like this:
display_thread process_thread
-------------- --------------
thread__comm_len
-> thread__comm_str
-> __thread__comm_str(thread)
thread__delete
-> comm__free
-> comm_str__put
-> zfree(&cs->str)
-> thread->comm_len = strlen(comm);
Since in single thread phase, perf_singlethreaded is true, down_read and
down_write can not work to avoid concurrency problems.
This patch put perf_set_singlethreaded to the function tail to expand the
multithreaded phase range, make display_thread and process_thread run
safe.

Signed-off-by: Hangliang Lai <laihangliang1@huawei.com>
Reviewed-by: Yunfeng Ye <yeyunfeng@huawei.com>
---
v2 -> v3
- Sorry for my misunderstanding, patch v3 makes perf_set_multithreaded
unconditional after synthesis and set_singlethread in the end.

tools/perf/builtin-top.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index d4b5b02bab73..ae96ddaf85c4 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -1273,8 +1273,7 @@ static int __cmd_top(struct perf_top *top)
top->evlist->core.threads, true, false,
top->nr_threads_synthesize);

- if (top->nr_threads_synthesize > 1)
- perf_set_singlethreaded();
+ perf_set_multithreaded();

if (perf_hpp_list.socket) {
ret = perf_env__read_cpu_topology_map(&perf_env);
@@ -1352,6 +1351,7 @@ static int __cmd_top(struct perf_top *top)
out_join_thread:
cond_signal(&top->qe.cond);
pthread_join(thread_process, NULL);
+ perf_set_singlethreaded();
return ret;
}

--
2.33.0
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