On 2024-10-01, Tycho Andersen <tycho@tycho.pizza> wrote: > From: Tycho Andersen <tandersen@xxxxxxxxxxx> > > 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 Reviewed-by: Aleksa Sarai <cyphar@xxxxxxxxxx> > Signed-off-by: Tycho Andersen <tandersen@xxxxxxxxxxx> > Suggested-by: Zbigniew Jędrzejewski-Szmek <zbyszek@xxxxxxxxx> > CC: Aleksa Sarai <cyphar@xxxxxxxxxx> > 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/>
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