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authorAlexei Starovoitov <ast@kernel.org>2018-05-21 19:22:29 -0700
committerDavid S. Miller <davem@davemloft.net>2018-05-23 13:23:39 -0400
commit449325b52b7a6208f65ed67d3484fd7b7184477b (patch)
treec7fa03daa69b6b4ad272b42fc8b56e4413492c83 /fs/exec.c
parent1fe8c06c4a0d3b589f076cd00c25082840f10423 (diff)
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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 'fs/exec.c')
-rw-r--r--fs/exec.c38
1 files changed, 29 insertions, 9 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 183059c427b9..30a36c2a39bf 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1706,14 +1706,13 @@ static int exec_binprm(struct linux_binprm *bprm)
/*
* sys_execve() executes a new program.
*/
-static int do_execveat_common(int fd, struct filename *filename,
- struct user_arg_ptr argv,
- struct user_arg_ptr envp,
- int flags)
+static int __do_execve_file(int fd, struct filename *filename,
+ struct user_arg_ptr argv,
+ struct user_arg_ptr envp,
+ int flags, struct file *file)
{
char *pathbuf = NULL;
struct linux_binprm *bprm;
- struct file *file;
struct files_struct *displaced;
int retval;
@@ -1752,7 +1751,8 @@ static int do_execveat_common(int fd, struct filename *filename,
check_unsafe_exec(bprm);
current->in_execve = 1;
- file = do_open_execat(fd, filename, flags);
+ if (!file)
+ file = do_open_execat(fd, filename, flags);
retval = PTR_ERR(file);
if (IS_ERR(file))
goto out_unmark;
@@ -1760,7 +1760,9 @@ static int do_execveat_common(int fd, struct filename *filename,
sched_exec();
bprm->file = file;
- if (fd == AT_FDCWD || filename->name[0] == '/') {
+ if (!filename) {
+ bprm->filename = "none";
+ } else if (fd == AT_FDCWD || filename->name[0] == '/') {
bprm->filename = filename->name;
} else {
if (filename->name[0] == '\0')
@@ -1826,7 +1828,8 @@ static int do_execveat_common(int fd, struct filename *filename,
task_numa_free(current);
free_bprm(bprm);
kfree(pathbuf);
- putname(filename);
+ if (filename)
+ putname(filename);
if (displaced)
put_files_struct(displaced);
return retval;
@@ -1849,10 +1852,27 @@ out_files:
if (displaced)
reset_files_struct(displaced);
out_ret:
- putname(filename);
+ if (filename)
+ putname(filename);
return retval;
}
+static int do_execveat_common(int fd, struct filename *filename,
+ struct user_arg_ptr argv,
+ struct user_arg_ptr envp,
+ int flags)
+{
+ return __do_execve_file(fd, filename, argv, envp, flags, NULL);
+}
+
+int do_execve_file(struct file *file, void *__argv, void *__envp)
+{
+ struct user_arg_ptr argv = { .ptr.native = __argv };
+ struct user_arg_ptr envp = { .ptr.native = __envp };
+
+ return __do_execve_file(AT_FDCWD, NULL, argv, envp, 0, file);
+}
+
int do_execve(struct filename *filename,
const char __user *const __user *__argv,
const char __user *const __user *__envp)