[PATCH][RFC] fs/exec.c: provide the correct process pid to the pipe helper

Will Drewry
2010-09-16T19:00:46Z

format_corename uses task_tgid_vnr to provide the numeric pid of a
core-dumping process. For file-based coredumps, this is perfectly
satisfactory. However, when the core_pattern contains a pipe, the
substituted PID is invalid in the namespace of the core_pattern pipe
helper, the init namespace.

By changing this, any core collector may now find the process in the
init namespace /proc. This helps with VFS namespacing too since the
mount root is available via /proc. Unfortunately, it does not help in
cases of more complex namespacing, like net namespaces. For that, the
helper thread will need to be migrated to the core-dump namespaces.

I have a separate patch series which implements migrating the
____call_usermodehelper thread to the coredump namespace, but it adds a
fair amount of complexity which might be better handled by someone who
understands that code. I'm happy to mail it out as well though (it
works, but I don't assign a namespaced pid which may open up issues on
its own).

Any and all comments, feedback will be appreciated!

Signed-off-by: Will Drewry <wad@chromium.org>
---
fs/exec.c | 11 +++++++++--
1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 828dd24..0b8a874 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1467,6 +1467,13 @@ static int format_corename(char *corename, long signr)
char *const out_end = corename + CORENAME_MAX_SIZE;
int rc;
int pid_in_pattern = 0;
+ pid_t pid = task_tgid_vnr(current);
+
+ /* The pipe helper runs in the init namespace and should
+ * receive the matching pid until that changes.
+ */
+ if (ispipe)
+ pid = task_tgid_nr(current);

/* Repeat as long as we have more pattern to process and more output
space */
@@ -1489,7 +1496,7 @@ static int format_corename(char *corename, long signr)
case 'p':
pid_in_pattern = 1;
rc = snprintf(out_ptr, out_end - out_ptr,
- "%d", task_tgid_vnr(current));
+ "%d", pid);
if (rc > out_end - out_ptr)
goto out;
out_ptr += rc;
@@ -1568,7 +1575,7 @@ static int format_corename(char *corename, long signr)
* the filename. Do not do this for piped commands. */
if (!ispipe && !pid_in_pattern && core_uses_pid) {
rc = snprintf(out_ptr, out_end - out_ptr,
- ".%d", task_tgid_vnr(current));
+ ".%d", pid);
if (rc > out_end - out_ptr)
goto out;
out_ptr += rc;
--
1.7.0.4