From: Tycho Andersen <tander...@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. Signed-off-by: Tycho Andersen <tander...@netflix.com> Suggested-by: Zbigniew Jędrzejewski-Szmek <zbys...@in.waw.pl> CC: Aleksa Sarai <cyp...@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 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
