From: Rong Tao <rong...@cestc.cn> It is a bit troublesome to get cwd based on pid in bpf program, such as bpftrace example [1].
This patch therefore adds a new bpf_task_cwd_from_pid() kfunc which allows BPF programs to get cwd from a pid. [1] https://github.com/bpftrace/bpftrace/issues/3314 Signed-off-by: Rong Tao <rong...@cestc.cn> --- kernel/bpf/helpers.c | 45 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index b71e428ad936..0f32fbc997bb 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -24,6 +24,10 @@ #include <linux/bpf_mem_alloc.h> #include <linux/kasan.h> #include <linux/bpf_verifier.h> +#include <linux/fs.h> +#include <linux/fs_struct.h> +#include <linux/path.h> +#include <linux/string.h> #include "../../lib/kstrtox.h" @@ -2643,6 +2647,46 @@ __bpf_kfunc struct task_struct *bpf_task_from_vpid(s32 vpid) return p; } +/** + * bpf_task_cwd_from_pid - Get a task's absolute pathname of the current + * working directory from its pid. + * @pid: The pid of the task being looked up. + * @buf: The array pointed to by buf. + * @buf_len: buf length. + */ +__bpf_kfunc int bpf_task_cwd_from_pid(s32 pid, char *buf, u32 buf_len) +{ + struct path pwd; + char kpath[256], *path; + struct task_struct *task; + + if (!buf || buf_len == 0) + return -EINVAL; + + rcu_read_lock(); + task = pid_task(find_vpid(pid), PIDTYPE_PID); + if (!task) { + rcu_read_unlock(); + return -ESRCH; + } + task_lock(task); + if (!task->fs) { + task_unlock(task); + return -ENOENT; + } + get_fs_pwd(task->fs, &pwd); + task_unlock(task); + rcu_read_unlock(); + + path = d_path(&pwd, kpath, sizeof(kpath)); + path_put(&pwd); + if (IS_ERR(path)) + return PTR_ERR(path); + + strncpy(buf, path, buf_len); + return 0; +} + /** * bpf_dynptr_slice() - Obtain a read-only pointer to the dynptr data. * @p: The dynptr whose data slice to retrieve @@ -3314,6 +3358,7 @@ BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL) #endif BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_task_from_vpid, KF_ACQUIRE | KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_task_cwd_from_pid, KF_RET_NULL) BTF_ID_FLAGS(func, bpf_throw) #ifdef CONFIG_BPF_EVENTS BTF_ID_FLAGS(func, bpf_send_signal_task, KF_TRUSTED_ARGS) -- 2.49.0
