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Subject[PATCH v3 1/1] bpf: Drop unprotected find_vpid() in favour of find_get_pid()
Date
The documentation for find_vpid() clearly states:

"Must be called with the tasklist_lock or rcu_read_lock() held."

Presently we do neither.

Let's use find_get_pid() which searches for the vpid, then takes a
reference to it preventing early free, all within the safety of
rcu_read_lock(). Once we have our reference we can safely make use of
it up until the point it is put.

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Song Liu <song@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Stanislav Fomichev <sdf@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: bpf@vger.kernel.org
Fixes: 41bdc4b40ed6f ("bpf: introduce bpf subcommand BPF_TASK_FD_QUERY")
Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Lee Jones <lee@kernel.org>
---

v1 => v2:
* Commit log update - description - no code differences

v2 => v3:
* Commit log update - spelling of find_vpid() - no code differences

kernel/bpf/syscall.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 83c7136c5788d..c20cff30581c4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4385,6 +4385,7 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
const struct perf_event *event;
struct task_struct *task;
struct file *file;
+ struct pid *ppid;
int err;

if (CHECK_ATTR(BPF_TASK_FD_QUERY))
@@ -4396,7 +4397,9 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
if (attr->task_fd_query.flags != 0)
return -EINVAL;

- task = get_pid_task(find_vpid(pid), PIDTYPE_PID);
+ ppid = find_get_pid(pid);
+ task = get_pid_task(ppid, PIDTYPE_PID);
+ put_pid(ppid);
if (!task)
return -ENOENT;

--
2.37.1.559.g78731f0fdb-goog
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