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Date: Tue, 26 Oct 2021 09:56:15 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
Petr Mladek <pmladek@...e.com>,
Peter Zijlstra <peterz@...radead.org>,
Al Viro <viro@...iv.linux.org.uk>,
Valentin Schneider <valentin.schneider@....com>,
Qiang Zhang <qiang.zhang@...driver.com>,
robdclark <robdclark@...omium.org>,
christian <christian@...uner.io>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
David Miller <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
john fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
dennis.dalessandro@...nelisnetworks.com,
mike.marciniszyn@...nelisnetworks.com, dledford@...hat.com,
jgg@...pe.ca, linux-rdma@...r.kernel.org,
netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
"linux-perf-use." <linux-perf-users@...r.kernel.org>,
linux-fsdevel@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
kernel test robot <oliver.sang@...el.com>,
kbuild test robot <lkp@...el.com>,
Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH v6 05/12] elfcore: make prpsinfo always get a nul
terminated task comm
On Tue, Oct 26, 2021 at 5:18 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Oct 25, 2021 at 08:33:08AM +0000, Yafang Shao wrote:
> > kernel test robot reported a -Wstringop-truncation warning after I
> > extend task comm from 16 to 24. Below is the detailed warning:
> >
> > fs/binfmt_elf.c: In function 'fill_psinfo.isra':
> > >> fs/binfmt_elf.c:1575:9: warning: 'strncpy' output may be truncated copying 16 bytes from a string of length 23 [-Wstringop-truncation]
> > 1575 | strncpy(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
> > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > This patch can fix this warning.
> >
> > Replacing strncpy() with strscpy_pad() can avoid this warning.
> >
> > This patch also replace the hard-coded 16 with TASK_COMM_LEN to make it
> > more compatible with task comm size change.
> >
> > I also verfied if it still work well when I extend the comm size to 24.
> > struct elf_prpsinfo is used to dump the task information in userspace
> > coredump or kernel vmcore. Below is the verfication of vmcore,
> >
> > crash> ps
> > PID PPID CPU TASK ST %MEM VSZ RSS COMM
> > 0 0 0 ffffffff9d21a940 RU 0.0 0 0 [swapper/0]
> > > 0 0 1 ffffa09e40f85e80 RU 0.0 0 0 [swapper/1]
> > > 0 0 2 ffffa09e40f81f80 RU 0.0 0 0 [swapper/2]
> > > 0 0 3 ffffa09e40f83f00 RU 0.0 0 0 [swapper/3]
> > > 0 0 4 ffffa09e40f80000 RU 0.0 0 0 [swapper/4]
> > > 0 0 5 ffffa09e40f89f80 RU 0.0 0 0 [swapper/5]
> > 0 0 6 ffffa09e40f8bf00 RU 0.0 0 0 [swapper/6]
> > > 0 0 7 ffffa09e40f88000 RU 0.0 0 0 [swapper/7]
> > > 0 0 8 ffffa09e40f8de80 RU 0.0 0 0 [swapper/8]
> > > 0 0 9 ffffa09e40f95e80 RU 0.0 0 0 [swapper/9]
> > > 0 0 10 ffffa09e40f91f80 RU 0.0 0 0 [swapper/10]
> > > 0 0 11 ffffa09e40f93f00 RU 0.0 0 0 [swapper/11]
> > > 0 0 12 ffffa09e40f90000 RU 0.0 0 0 [swapper/12]
> > > 0 0 13 ffffa09e40f9bf00 RU 0.0 0 0 [swapper/13]
> > > 0 0 14 ffffa09e40f98000 RU 0.0 0 0 [swapper/14]
> > > 0 0 15 ffffa09e40f9de80 RU 0.0 0 0 [swapper/15]
> >
> > It works well as expected.
> >
> > Reported-by: kernel test robot <lkp@...el.com>
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
> > Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Petr Mladek <pmladek@...e.com>
> > ---
> > fs/binfmt_elf.c | 2 +-
> > include/linux/elfcore-compat.h | 3 ++-
> > include/linux/elfcore.h | 4 ++--
> > 3 files changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index a813b70f594e..a4ba79fce2a9 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1572,7 +1572,7 @@ static int fill_psinfo(struct elf_prpsinfo *psinfo, struct task_struct *p,
> > SET_UID(psinfo->pr_uid, from_kuid_munged(cred->user_ns, cred->uid));
> > SET_GID(psinfo->pr_gid, from_kgid_munged(cred->user_ns, cred->gid));
> > rcu_read_unlock();
> > - strncpy(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
> > + strscpy_pad(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
>
> This should use get_task_comm().
>
Sure.
> >
> > return 0;
> > }
> > diff --git a/include/linux/elfcore-compat.h b/include/linux/elfcore-compat.h
> > index e272c3d452ce..afa0eb45196b 100644
> > --- a/include/linux/elfcore-compat.h
> > +++ b/include/linux/elfcore-compat.h
> > @@ -5,6 +5,7 @@
> > #include <linux/elf.h>
> > #include <linux/elfcore.h>
> > #include <linux/compat.h>
> > +#include <linux/sched.h>
> >
> > /*
> > * Make sure these layouts match the linux/elfcore.h native definitions.
> > @@ -43,7 +44,7 @@ struct compat_elf_prpsinfo
> > __compat_uid_t pr_uid;
> > __compat_gid_t pr_gid;
> > compat_pid_t pr_pid, pr_ppid, pr_pgrp, pr_sid;
> > - char pr_fname[16];
> > + char pr_fname[TASK_COMM_LEN];
> > char pr_psargs[ELF_PRARGSZ];
> > };
> >
> > diff --git a/include/linux/elfcore.h b/include/linux/elfcore.h
> > index 2aaa15779d50..8d79cd58b09a 100644
> > --- a/include/linux/elfcore.h
> > +++ b/include/linux/elfcore.h
> > @@ -65,8 +65,8 @@ struct elf_prpsinfo
> > __kernel_gid_t pr_gid;
> > pid_t pr_pid, pr_ppid, pr_pgrp, pr_sid;
> > /* Lots missing */
> > - char pr_fname[16]; /* filename of executable */
> > - char pr_psargs[ELF_PRARGSZ]; /* initial part of arg list */
> > + char pr_fname[TASK_COMM_LEN]; /* filename of executable */
> > + char pr_psargs[ELF_PRARGSZ]; /* initial part of arg list */
> > };
> >
> > static inline void elf_core_copy_regs(elf_gregset_t *elfregs, struct pt_regs *regs)
> > --
> > 2.17.1
> >
>
> These structs are externally parsed -- we can't change the size of
> pr_fname AFAICT.
>
Yes, they are parsed by crash utility and other tools.
I will keep pr_fname as-is.
--
Thanks
Yafang
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