On 2024-10-01, Aleksa Sarai cyphar@cyphar.com wrote:
On 2024-10-01, Tycho Andersen tycho@tycho.pizza wrote:
From: Tycho Andersen tandersen@netflix.com
Zbigniew mentioned at Linux Plumber's that systemd is interested in switching to execveat() for service execution, but can't, because the contents of /proc/pid/comm are the file descriptor which was used, instead of the path to the binary. This makes the output of tools like top and ps useless, especially in a world where most fds are opened CLOEXEC so the number is truly meaningless.
Change exec path to fix up /proc/pid/comm in the case where we have allocated one of these synthetic paths in bprm_init(). This way the actual exec machinery is unchanged, but cosmetically the comm looks reasonable to admins investigating things.
While I still think the argv[0] solution was semantically nicer, it seems this is enough to fix the systemd problem for most cases and so we can revisit the argv[0] discussion in another 10 years. :D
Of course, this assumes the busybox problem I mentioned really is not an issue. But at least this option is "less wrong" than using the fd number. I suspect we will eventually need the argv[0] thing.
Reviewed-by: Aleksa Sarai cyphar@cyphar.com
Signed-off-by: Tycho Andersen tandersen@netflix.com Suggested-by: Zbigniew Jędrzejewski-Szmek zbyszek@in.waw.pl CC: Aleksa Sarai cyphar@cyphar.com Link: https://github.com/uapi-group/kernel-features#set-comm-field-before-exec
v2: * drop the flag, everyone :) * change the rendered value to f_path.dentry->d_name.name instead of argv[0], Eric v3: * fix up subject line, Eric
fs/exec.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/fs/exec.c b/fs/exec.c index dad402d55681..9520359a8dcc 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1416,7 +1416,18 @@ int begin_new_exec(struct linux_binprm * bprm) set_dumpable(current->mm, SUID_DUMP_USER); perf_event_exec();
- __set_task_comm(me, kbasename(bprm->filename), true);
- /*
* If fdpath was set, execveat() made up a path that will* probably not be useful to admins running ps or similar.* Let's fix it up to be something reasonable.*/- if (bprm->fdpath) {
BUILD_BUG_ON(TASK_COMM_LEN > DNAME_INLINE_LEN);__set_task_comm(me, bprm->file->f_path.dentry->d_name.name, true);- } else {
__set_task_comm(me, kbasename(bprm->filename), true);- }
/* An exec changes our domain. We are no longer part of the thread group */
base-commit: baeb9a7d8b60b021d907127509c44507539c15e5
2.34.1
-- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH https://www.cyphar.com/