Re: [PATCH 1/2] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case
On Wed, Oct 30, 2024 at 02:37:31PM -0600, Tycho Andersen wrote: > From: Tycho Andersen > > 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. > > Signed-off-by: Tycho Andersen > Suggested-by: Zbigniew Jędrzejewski-Szmek > CC: Aleksa Sarai > Link: https://github.com/uapi-group/kernel-features#set-comm-field-before-exec > --- We finally went full circle back to what was originally proposed :) Reviewed-by: Christian Brauner
Re: [PATCH 1/2] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case
On Sat, Nov 02, 2024 at 11:29:55AM +, Zbigniew Jędrzejewski-Szmek wrote: > On Thu, Oct 31, 2024 at 03:10:37PM -0700, Kees Cook wrote: > > On Wed, 30 Oct 2024 14:37:31 -0600, Tycho Andersen wrote: > > > 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. > > > > > > [...] > > > > Applied to for-next/execve, thanks! > > > > [1/2] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case > > https://git.kernel.org/kees/c/7bdc6fc85c9a > > [2/2] selftests/exec: add a test for execveat()'s comm > > https://git.kernel.org/kees/c/bd104872311a > > I tested this with systemd compiled with -Dfexece=true and it all > seems to work fine. Thanks! Great; thank you! -- Kees Cook
Re: [PATCH 1/2] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case
On Thu, Oct 31, 2024 at 03:10:37PM -0700, Kees Cook wrote: > On Wed, 30 Oct 2024 14:37:31 -0600, Tycho Andersen wrote: > > 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. > > > > [...] > > Applied to for-next/execve, thanks! > > [1/2] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case > https://git.kernel.org/kees/c/7bdc6fc85c9a > [2/2] selftests/exec: add a test for execveat()'s comm > https://git.kernel.org/kees/c/bd104872311a I tested this with systemd compiled with -Dfexece=true and it all seems to work fine. Thanks! Zbyszek
Re: [PATCH 1/2] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case
On Wed, 30 Oct 2024 14:37:31 -0600, Tycho Andersen wrote: > 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. > > [...] Applied to for-next/execve, thanks! [1/2] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case https://git.kernel.org/kees/c/7bdc6fc85c9a [2/2] selftests/exec: add a test for execveat()'s comm https://git.kernel.org/kees/c/bd104872311a Take care, -- Kees Cook
[PATCH 1/2] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case
From: Tycho Andersen
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.
Signed-off-by: Tycho Andersen
Suggested-by: Zbigniew Jędrzejewski-Szmek
CC: Aleksa Sarai
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
v4: * switch to no flag, always rewrite approach, with some cleanup
suggested by Kees
---
fs/exec.c | 36 +++-
include/linux/binfmts.h | 1 +
2 files changed, 36 insertions(+), 1 deletion(-)
diff --git a/fs/exec.c b/fs/exec.c
index 6c53920795c2..3b559f598c74 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1347,7 +1347,16 @@ 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 argv0 was set, alloc_bprm() 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->argv0)
+ __set_task_comm(me, kbasename(bprm->argv0), true);
+ else
+ __set_task_comm(me, kbasename(bprm->filename), true);
/* An exec changes our domain. We are no longer part of the thread
group */
@@ -1497,9 +1506,28 @@ static void free_bprm(struct linux_binprm *bprm)
if (bprm->interp != bprm->filename)
kfree(bprm->interp);
kfree(bprm->fdpath);
+ kfree(bprm->argv0);
kfree(bprm);
}
+static int bprm_add_fixup_comm(struct linux_binprm *bprm,
+ struct user_arg_ptr argv)
+{
+ const char __user *p = get_user_arg_ptr(argv, 0);
+
+ /*
+* If p == NULL, let's just fall back to fdpath.
+*/
+ if (!p)
+ return 0;
+
+ bprm->argv0 = strndup_user(p, MAX_ARG_STRLEN);
+ if (bprm->argv0)
+ return 0;
+
+ return -EFAULT;
+}
+
static struct linux_binprm *alloc_bprm(int fd, struct filename *filename, int
flags)
{
struct linux_binprm *bprm;
@@ -1906,6 +1934,12 @@ static int do_execveat_common(int fd, struct filename
*filename,
goto out_ret;
}
+ if (unlikely(bprm->fdpath)) {
+ retval = bprm_add_fixup_comm(bprm, argv);
+ if (retval != 0)
+ goto out_free;
+ }
+
retval = count(argv, MAX_ARG_STRINGS);
if (retval == 0)
pr_warn_once("process '%s' launched '%s' with NULL argv: empty
string added\n",
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index e6c00e860951..bab5121a746b 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -55,6 +55,7 @@ struct linux_binprm {
of the time same as filename, but could be
different for binfmt_{misc,script} */
const char *fdpath; /* generated filename for execveat */
+ const char *argv0; /* argv0 from execveat */
unsigned interp_flags;
int execfd; /* File descriptor of the executable */
unsigned long loader, exec;
base-commit: c1e939a21eb111a6d6067b38e8e04b8809b64c4e
--
2.34.1
