On Fri, Sep 27, 2024 at 10:45:58AM -0500, Eric W. Biederman wrote: > Tycho Andersen <tycho@tycho.pizza> writes: > > > 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. > > Perhaps change the subject to match the code. > > > 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 > > --- > > 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); > > We can just do this regardless of bprm->fdpath. > > It will be a change of behavior on when executing symlinks and possibly > mount points but I don't think we care. If we do then we can add make > it conditional with "if (bprm->fdpath)" > > At the very least using the above version unconditionally ought to flush > out any bugs. I'm not super comfortable doing this regardless of bprm->fdpath; that seems like too many cases getting changed. Can we just leave it as depending on bprm->fdpath? Also, is d_name.name always going to be set? e.g. what about memfd, etc? -- Kees Cook
