Messages in this thread Patch in this message | | | From | Lee Jones <> | Subject | [PATCH 1/1] bpf: Drop unprotected find_vpid() in favour of find_get_pid() | Date | Thu, 21 Jul 2022 12:14:30 +0100 |
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The documentation for find_pid() clearly states:
"Must be called with the tasklist_lock or rcu_read_lock() held."
Presently we do neither.
In an ideal world we would wrap the in-lined call to find_vpid() along with get_pid_task() in the suggested rcu_read_lock() and have done. However, looking at get_pid_task()'s internals, it already does that independently, so this would lead to deadlock.
Instead, we'll 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: Jiri Olsa <jolsa@kernel.org> Cc: bpf@vger.kernel.org Fixes: 41bdc4b40ed6f ("bpf: introduce bpf subcommand BPF_TASK_FD_QUERY") Signed-off-by: Lee Jones <lee@kernel.org> --- 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; -- 2.37.0.170.g444d1eabd0-goog
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