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authorAlexei Starovoitov <ast@kernel.org>2018-05-22 05:22:29 +0300
committerDavid S. Miller <davem@davemloft.net>2018-05-23 20:23:39 +0300
commit449325b52b7a6208f65ed67d3484fd7b7184477b (patch)
treec7fa03daa69b6b4ad272b42fc8b56e4413492c83 /include/linux/umh.h
parent1fe8c06c4a0d3b589f076cd00c25082840f10423 (diff)
downloadlinux-449325b52b7a6208f65ed67d3484fd7b7184477b.tar.xz
umh: introduce fork_usermode_blob() helper
Introduce helper: int fork_usermode_blob(void *data, size_t len, struct umh_info *info); struct umh_info { struct file *pipe_to_umh; struct file *pipe_from_umh; pid_t pid; }; that GPLed kernel modules (signed or unsigned) can use it to execute part of its own data as swappable user mode process. The kernel will do: - allocate a unique file in tmpfs - populate that file with [data, data + len] bytes - user-mode-helper code will do_execve that file and, before the process starts, the kernel will create two unix pipes for bidirectional communication between kernel module and umh - close tmpfs file, effectively deleting it - the fork_usermode_blob will return zero on success and populate 'struct umh_info' with two unix pipes and the pid of the user process As the first step in the development of the bpfilter project the fork_usermode_blob() helper is introduced to allow user mode code to be invoked from a kernel module. The idea is that user mode code plus normal kernel module code are built as part of the kernel build and installed as traditional kernel module into distro specified location, such that from a distribution point of view, there is no difference between regular kernel modules and kernel modules + umh code. Such modules can be signed, modprobed, rmmod, etc. The use of this new helper by a kernel module doesn't make it any special from kernel and user space tooling point of view. Such approach enables kernel to delegate functionality traditionally done by the kernel modules into the user space processes (either root or !root) and reduces security attack surface of the new code. The buggy umh code would crash the user process, but not the kernel. Another advantage is that umh code of the kernel module can be debugged and tested out of user space (e.g. opening the possibility to run clang sanitizers, fuzzers or user space test suites on the umh code). In case of the bpfilter project such architecture allows complex control plane to be done in the user space while bpf based data plane stays in the kernel. Since umh can crash, can be oom-ed by the kernel, killed by the admin, the kernel module that uses them (like bpfilter) needs to manage life time of umh on its own via two unix pipes and the pid of umh. The exit code of such kernel module should kill the umh it started, so that rmmod of the kernel module will cleanup the corresponding umh. Just like if the kernel module does kmalloc() it should kfree() it in the exit code. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/umh.h')
-rw-r--r--include/linux/umh.h12
1 files changed, 12 insertions, 0 deletions
diff --git a/include/linux/umh.h b/include/linux/umh.h
index 244aff638220..5c812acbb80a 100644
--- a/include/linux/umh.h
+++ b/include/linux/umh.h
@@ -22,8 +22,10 @@ struct subprocess_info {
const char *path;
char **argv;
char **envp;
+ struct file *file;
int wait;
int retval;
+ pid_t pid;
int (*init)(struct subprocess_info *info, struct cred *new);
void (*cleanup)(struct subprocess_info *info);
void *data;
@@ -38,6 +40,16 @@ call_usermodehelper_setup(const char *path, char **argv, char **envp,
int (*init)(struct subprocess_info *info, struct cred *new),
void (*cleanup)(struct subprocess_info *), void *data);
+struct subprocess_info *call_usermodehelper_setup_file(struct file *file,
+ int (*init)(struct subprocess_info *info, struct cred *new),
+ void (*cleanup)(struct subprocess_info *), void *data);
+struct umh_info {
+ struct file *pipe_to_umh;
+ struct file *pipe_from_umh;
+ pid_t pid;
+};
+int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
+
extern int
call_usermodehelper_exec(struct subprocess_info *info, int wait);