On Wed, Aug 28, 2024 at 12:15:40PM GMT, Alejandro Colomar wrote: > Hi Yafang, > > On Wed, Aug 28, 2024 at 11:03:14AM GMT, Yafang Shao wrote: > > We want to eliminate the use of __get_task_comm() for the following > > reasons: > > > > - The task_lock() is unnecessary > > Quoted from Linus [0]: > > : Since user space can randomly change their names anyway, using locking > > : was always wrong for readers (for writers it probably does make sense > > : to have some lock - although practically speaking nobody cares there > > : either, but at least for a writer some kind of race could have > > : long-term mixed results > > > > - The BUILD_BUG_ON() doesn't add any value > > The only requirement is to ensure that the destination buffer is a valid > > array. > > > > - Zeroing is not necessary in current use cases > > To avoid confusion, we should remove it. Moreover, not zeroing could > > potentially make it easier to uncover bugs. If the caller needs a > > zero-padded task name, it should be explicitly handled at the call site. > > > > Suggested-by: Linus Torvalds <torva...@linux-foundation.org> > > Link: > > https://lore.kernel.org/all/CAHk-=wivfrF0_zvf+oj6==Sh=-npjoop8chlpefafv0onyt...@mail.gmail.com > > [0] > > Link: > > https://lore.kernel.org/all/CAHk-=whwtuc-ajmgjveaetkomemfstwkwu99v7+b6ayhmma...@mail.gmail.com/ > > Suggested-by: Alejandro Colomar <a...@kernel.org> > > Link: > > https://lore.kernel.org/all/2jxak5v6dfxlpbxhpm3ey7oup4g2lnr3ueurfbosf5wdo65dk4@srb3hsk72zwq > > Signed-off-by: Yafang Shao <laoar.s...@gmail.com> > > Cc: Alexander Viro <v...@zeniv.linux.org.uk> > > Cc: Christian Brauner <brau...@kernel.org> > > Cc: Jan Kara <j...@suse.cz> > > Cc: Eric Biederman <ebied...@xmission.com> > > Cc: Kees Cook <keesc...@chromium.org> > > Cc: Alexei Starovoitov <alexei.starovoi...@gmail.com> > > Cc: Matus Jokay <matus.jo...@stuba.sk> > > Cc: Alejandro Colomar <a...@kernel.org> > > Cc: "Serge E. Hallyn" <se...@hallyn.com> > > --- > > fs/exec.c | 10 ---------- > > fs/proc/array.c | 2 +- > > include/linux/sched.h | 32 ++++++++++++++++++++++++++------ > > kernel/kthread.c | 2 +- > > 4 files changed, 28 insertions(+), 18 deletions(-) > > > > [...] > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index f8d150343d42..c40b95a79d80 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > [...] > > > @@ -1914,10 +1917,27 @@ static inline void set_task_comm(struct task_struct > > *tsk, const char *from) > > __set_task_comm(tsk, from, false); > > } > > > > -extern char *__get_task_comm(char *to, size_t len, struct task_struct > > *tsk); > > +/* > > [...] > > > + * - ARRAY_SIZE() can help ensure that @buf is indeed an array. > > + */ > > #define get_task_comm(buf, tsk) ({ \ > > - BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \ > > - __get_task_comm(buf, sizeof(buf), tsk); \ > > + strscpy(buf, (tsk)->comm, ARRAY_SIZE(buf)); \ > > I see that there's a two-argument macro > > #define strscpy(dst, src) sized_strscpy(dst, src, sizeof(dst)) > > which is used in patch 2/8 > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > index 6f0d6fb6523f..e4ef5e57dde9 100644 > --- a/kernel/auditsc.c > +++ b/kernel/auditsc.c > @@ -2730,7 +2730,7 @@ void __audit_ptrace(struct task_struct *t) > context->target_uid = task_uid(t); > context->target_sessionid = audit_get_sessionid(t); > security_task_getsecid_obj(t, &context->target_sid); > - memcpy(context->target_comm, t->comm, TASK_COMM_LEN); > + strscpy(context->target_comm, t->comm); > } > > /**
Ahh, the actual generic definition is in <include/linux/string.h>.
You could do
diff --git i/include/linux/string.h w/include/linux/string.h
index 9edace076ddb..060504719904 100644
--- i/include/linux/string.h
+++ w/include/linux/string.h
@@ -76,11 +76,11 @@ ssize_t sized_strscpy(char *, const char *, size_t);
* known size.
*/
#define __strscpy0(dst, src, ...) \
- sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
+ sized_strscpy(dst, src, ARRAY_SIZE(dst))
#define __strscpy1(dst, src, size) sized_strscpy(dst, src, size)
#define __strscpy_pad0(dst, src, ...) \
- sized_strscpy_pad(dst, src, sizeof(dst) + __must_be_array(dst))
+ sized_strscpy_pad(dst, src, ARRAY_SIZE(dst))
#define __strscpy_pad1(dst, src, size) sized_strscpy_pad(dst, src,
size)
/**
>
> I propose modifying that macro to use ARRAY_SIZE() instead of sizeof(),
> and then calling that macro here too. That would not only make sure
> that this is an array, but make sure that every call to that macro is an
> array. An if there are macros for similar string functions that reduce
> the argument with a usual sizeof(), the same thing could be done to
> those too.
>
> Have a lovley day!
> Alex
>
> > + buf; \
> > })
> >
> > #ifdef CONFIG_SMP
> > diff --git a/kernel/kthread.c b/kernel/kthread.c
> > index f7be976ff88a..7d001d033cf9 100644
> > --- a/kernel/kthread.c
> > +++ b/kernel/kthread.c
> > @@ -101,7 +101,7 @@ void get_kthread_comm(char *buf, size_t buf_size,
> > struct task_struct *tsk)
> > struct kthread *kthread = to_kthread(tsk);
> >
> > if (!kthread || !kthread->full_name) {
> > - __get_task_comm(buf, buf_size, tsk);
> > + strscpy(buf, tsk->comm, buf_size);
> > return;
> > }
> >
> > --
> > 2.43.5
> >
>
> --
> <https://www.alejandro-colomar.es/>
--
<https://www.alejandro-colomar.es/>
signature.asc
Description: PGP signature
