[PATCH v2 bpf-next 6/9] bpf: add acquire/release based BPF kfuncs for fs_struct's paths

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Add the ability to obtain a reference on the root and pwd paths which
are nested within the fs_struct associated with a supplied
task_struct. Both fs_struct's root and pwd are commonly operated on in
BPF LSM program types and at times are further handed off to BPF
helpers and such. There needs to be a mechanism that supports BPF LSM
program types the ability to obtain stable handles to such paths in
order to avoid possible memory corruption bugs [0].

We provide this mechanism through the introduction of the following
new KF_ACQUIRE/KF_RELEASE BPF kfuncs:

struct path *bpf_get_task_fs_root(struct task_struct *task);
struct path *bpf_get_task_fs_pwd(struct task_struct *task);
void bpf_put_path(struct path *path);

Note that bpf_get_task_fs_root() and bpf_get_task_fs_pwd() are
effectively open-coded variants of the in-kernel helpers get_fs_root()
and get_fs_pwd(). We don't lean on these in-kernel helpers directly
within the newly introduced BPF kfuncs as leaning on them would be
rather awkward as we're wanting to return referenced path pointers
directly BPF LSM program types.

[0] https://lore.kernel.org/bpf/CAG48ez0ppjcT=QxU-jtCUfb5xQb3mLr=5FcwddF_VKfEBPs_Dg@xxxxxxxxxxxxxx/

Signed-off-by: Matt Bobrowski <mattbobrowski@xxxxxxxxxx>
---
 kernel/trace/bpf_trace.c | 83 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 539c58db74d7..84fd87ead20c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -10,6 +10,7 @@
 #include <linux/bpf_perf_event.h>
 #include <linux/btf.h>
 #include <linux/filter.h>
+#include <linux/fs_struct.h>
 #include <linux/uaccess.h>
 #include <linux/ctype.h>
 #include <linux/kprobes.h>
@@ -1569,6 +1570,83 @@ __bpf_kfunc void bpf_put_file(struct file *f)
 	fput(f);
 }
 
+/**
+ * bpf_get_task_fs_root - get a reference on the fs_struct's root path for the
+ * 			  supplied task_struct
+ * @Task: task_struct of which the fs_struct's root path to get a reference on
+ *
+ * Get a reference on the root path nested within the fs_struct of the
+ * associated *task*. The referenced path retruned from this kfunc must be
+ * released using bpf_put_path().
+ *
+ * Return: A referenced path pointer to the root path nested within the
+ * fs_struct of the supplied *task*, or NULL.
+ */
+__bpf_kfunc struct path *bpf_get_task_fs_root(struct task_struct *task)
+{
+	struct path *root;
+	struct fs_struct *fs;
+
+	task_lock(task);
+	fs = task->fs;
+	if (unlikely(fs)) {
+		task_unlock(task);
+		return NULL;
+	}
+
+	spin_lock(&fs->lock);
+	root = &fs->root;
+	path_get(root);
+	spin_unlock(&fs->lock);
+	task_unlock(task);
+
+	return root;
+}
+
+/**
+ * bpf_get_task_fs_pwd - get a reference on the fs_struct's pwd path for the
+ * 			 supplied task_struct
+ * @task: task_struct of which the fs_struct's pwd path to get a reference on
+ *
+ * Get a reference on the pwd path nested within the fs_struct of the associated
+ * *task*. The referenced path retruned from this kfunc must be released using
+ * bpf_put_path().
+ *
+ * Return: A referenced path pointer to the root path nested within the
+ * fs_struct of the supplied *task*, or NULL.
+ */
+__bpf_kfunc struct path *bpf_get_task_fs_pwd(struct task_struct *task)
+{
+	struct path *pwd;
+	struct fs_struct *fs;
+
+	task_lock(task);
+	fs = task->fs;
+	if (unlikely(fs)) {
+		task_unlock(task);
+		return NULL;
+	}
+
+	spin_lock(&fs->lock);
+	pwd = &fs->pwd;
+	path_get(pwd);
+	spin_unlock(&fs->lock);
+	task_unlock(task);
+
+	return pwd;
+}
+
+/**
+ * bpf_put_path - put a reference on the supplied path
+ * @path: path of which to put a reference on
+ *
+ * Put a reference on the supplied *path*.
+  */
+__bpf_kfunc void bpf_put_path(struct path *path)
+{
+	path_put(path);
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(lsm_kfunc_set_ids)
@@ -1580,6 +1658,11 @@ BTF_ID_FLAGS(func, bpf_get_task_exe_file,
 BTF_ID_FLAGS(func, bpf_get_mm_exe_file,
 	     KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_put_file, KF_RELEASE | KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_get_task_fs_root,
+	     KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_get_task_fs_pwd,
+	     KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_put_path, KF_RELEASE | KF_SLEEPABLE)
 BTF_KFUNCS_END(lsm_kfunc_set_ids)
 
 static int bpf_lsm_kfunc_filter(const struct bpf_prog *prog, u32 kfunc_id)
-- 
2.44.0.278.ge034bb2e1d-goog

/M




[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux