[PATCH][RFC] v2 exec: move core_pattern pipe helper into the crashing namespace

Will Drewry
2010-09-18T03:15:24Z

Presently, a core_pattern pipe endpoint will be run in the init
namespace. It will receive the virtual pid (task_tgid_vnr->%p) of the
core dumping process but will have no access to that processes /proc
without walking the init namespace /proc looking through all the global
pids until it finds the one it thinks matches.

One option for fixing this is to change the reported pid:
https://patchwork.kernel.org/patch/185912/
However, it's unclear if it is desirable for the core_pattern to run
outside the namespace. In particular, it can easily access the mounts
via /proc/[pid_nr]/root, but if there is a net namespace, it will not
have access. (Originally introduced in 2007 in commit
b488893a390edfe027bae7a46e9af8083e740668 )

Instead, this change implements the more complex option two. It
migrates the ____call_usermodehelper() thread into the same namespaces
as the dumping process. It does not assign a pid in that namespace so
the collector will appear to be pid 0 in the namespace.

Signed-off-by: Will Drewry <wad@chromium.org>

---
v2: dropped patch 1/2
removed use of new copy_namespaces_unattached (oleg@redhat.com)
moved pipe_params into coredump_params (nhorman@tuxdriver.com)

fs/exec.c | 46 +++++++++++++++++++++++++++++++++++++++++++++-
include/linux/binfmts.h | 9 +++++++++
2 files changed, 54 insertions(+), 1 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 828dd24..4cbb735 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -51,6 +51,7 @@
#include <linux/audit.h>
#include <linux/tracehook.h>
#include <linux/kmod.h>
+#include <linux/nsproxy.h>
#include <linux/fsnotify.h>
#include <linux/fs_struct.h>
#include <linux/pipe_fs_i.h>
@@ -1820,7 +1821,32 @@ static int umh_pipe_setup(struct subprocess_info *info)
struct file *rp, *wp;
struct fdtable *fdt;
struct coredump_params *cp = (struct coredump_params *)info->data;
- struct files_struct *cf = current->files;
+ struct coredump_pipe_params *pipe_params = &cp->pipe_params;
+ struct task_struct *tsk = current;
+ struct files_struct *cf = tsk->files;
+ struct fs_struct *cfs = tsk->fs;
+
+ /* Migrate this thread into the crashing namespaces, but
+ * don't change its pid struct to avoid breaking any other
+ * dependencies. This will mean the process is pid=0 if it
+ * was migrated into a pid namespace.
+ */
+ if (pipe_params->nsproxy && pipe_params->fs) {
+ int kill;
+ switch_task_namespaces(tsk, pipe_params->nsproxy);
+ pipe_params->nsproxy = NULL;
+
+ task_lock(tsk);
+ tsk->fs = pipe_params->fs;
+ task_unlock(tsk);
+ pipe_params->fs = NULL;
+ /* Clean up the previous fs struct */
+ write_lock(&cfs->lock);
+ kill = !--cfs->users;
+ write_unlock(&cfs->lock);
+ if (kill)
+ free_fs_struct(cfs);
+ }

wp = create_write_pipe(0);
if (IS_ERR(wp))
@@ -1950,10 +1976,28 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
goto fail_dropcount;
}

+ /* Run the core_collector in the crashing namespaces */
+ cprm.pipe_params.fs = copy_fs_struct(current->fs);
+ if (!cprm.pipe_params.fs) {
+ printk(KERN_WARNING "%s failed to copy fs\n",
+ __func__);
+ argv_free(helper_argv);
+ goto fail_dropcount;
+ }
+ get_nsproxy(current->nsproxy);
+ cprm.pipe_params.nsproxy = current->nsproxy;
+
retval = call_usermodehelper_fns(helper_argv[0], helper_argv,
NULL, UMH_WAIT_EXEC, umh_pipe_setup,
NULL, &cprm);
argv_free(helper_argv);
+ /* nsproxy and fs will survive if call_usermodehelper_fns hits
+ * ENOMEM prior to creating a new thread.
+ */
+ if (cprm.pipe_params.nsproxy)
+ put_nsproxy(cprm.pipe_params.nsproxy);
+ if (cprm.pipe_params.fs) /* not in use by anything else */
+ free_fs_struct(cprm.pipe_params.fs);
if (retval) {
printk(KERN_INFO "Core dump to %s pipe failed\n",
corename);
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index a065612..2629603 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -68,6 +68,12 @@ struct linux_binprm{

#define BINPRM_MAX_RECURSION 4

+/* Parameters to be passed to a pipe target during coredump */
+struct coredump_pipe_params {
+ struct nsproxy *nsproxy;
+ struct fs_struct *fs;
+};
+
/* Function parameter for binfmt->coredump */
struct coredump_params {
long signr;
@@ -75,6 +81,9 @@ struct coredump_params {
struct file *file;
unsigned long limit;
unsigned long mm_flags;
+ union {
+ struct coredump_pipe_params pipe_params;
+ };
};

/*
--
1.7.0.4