* [PATCH] fcntl: Distribute switch variables for initialization
@ 2020-02-20 6:22 Kees Cook
2020-03-03 4:41 ` Kees Cook
0 siblings, 1 reply; 4+ messages in thread
From: Kees Cook @ 2020-02-20 6:22 UTC (permalink / raw)
To: Jeff Layton, J. Bruce Fields
Cc: Alexander Potapenko, Kees Cook, linux-fsdevel, linux-kernel
Variables declared in a switch statement before any case statements
cannot be automatically initialized with compiler instrumentation (as
they are not part of any execution flow). With GCC's proposed automatic
stack variable initialization feature, this triggers a warning (and they
don't get initialized). Clang's automatic stack variable initialization
(via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
doesn't initialize such variables[1]. Note that these warnings (or silent
skipping) happen before the dead-store elimination optimization phase,
so even when the automatic initializations are later elided in favor of
direct initializations, the warnings remain.
To avoid these problems, move such variables into the "case" where
they're used or lift them up into the main function body.
fs/fcntl.c: In function ‘send_sigio_to_task’:
fs/fcntl.c:738:20: warning: statement will never be executed [-Wswitch-unreachable]
738 | kernel_siginfo_t si;
| ^~
[1] https://bugs.llvm.org/show_bug.cgi?id=44916
Signed-off-by: Kees Cook <keescook@chromium.org>
---
fs/fcntl.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 9bc167562ee8..2e4c0fa2074b 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -735,8 +735,9 @@ static void send_sigio_to_task(struct task_struct *p,
return;
switch (signum) {
- kernel_siginfo_t si;
- default:
+ default: {
+ kernel_siginfo_t si;
+
/* Queue a rt signal with the appropriate fd as its
value. We use SI_SIGIO as the source, not
SI_KERNEL, since kernel signals always get
@@ -769,6 +770,7 @@ static void send_sigio_to_task(struct task_struct *p,
si.si_fd = fd;
if (!do_send_sig_info(signum, &si, p, type))
break;
+ }
/* fall-through - fall back on the old plain SIGIO signal */
case 0:
do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, type);
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] fcntl: Distribute switch variables for initialization
2020-02-20 6:22 [PATCH] fcntl: Distribute switch variables for initialization Kees Cook
@ 2020-03-03 4:41 ` Kees Cook
2020-03-03 15:55 ` Jeff Layton
0 siblings, 1 reply; 4+ messages in thread
From: Kees Cook @ 2020-03-03 4:41 UTC (permalink / raw)
To: Jeff Layton, J. Bruce Fields, Jens Axboe, Al Viro
Cc: Alexander Potapenko, linux-fsdevel, linux-kernel
On Wed, Feb 19, 2020 at 10:22:43PM -0800, Kees Cook wrote:
> Variables declared in a switch statement before any case statements
> cannot be automatically initialized with compiler instrumentation (as
> they are not part of any execution flow). With GCC's proposed automatic
> stack variable initialization feature, this triggers a warning (and they
> don't get initialized). Clang's automatic stack variable initialization
> (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> doesn't initialize such variables[1]. Note that these warnings (or silent
> skipping) happen before the dead-store elimination optimization phase,
> so even when the automatic initializations are later elided in favor of
> direct initializations, the warnings remain.
>
> To avoid these problems, move such variables into the "case" where
> they're used or lift them up into the main function body.
>
> fs/fcntl.c: In function ‘send_sigio_to_task’:
> fs/fcntl.c:738:20: warning: statement will never be executed [-Wswitch-unreachable]
> 738 | kernel_siginfo_t si;
> | ^~
>
> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
Ping. Can someone pick this up, please?
Thanks!
-Kees
> ---
> fs/fcntl.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index 9bc167562ee8..2e4c0fa2074b 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -735,8 +735,9 @@ static void send_sigio_to_task(struct task_struct *p,
> return;
>
> switch (signum) {
> - kernel_siginfo_t si;
> - default:
> + default: {
> + kernel_siginfo_t si;
> +
> /* Queue a rt signal with the appropriate fd as its
> value. We use SI_SIGIO as the source, not
> SI_KERNEL, since kernel signals always get
> @@ -769,6 +770,7 @@ static void send_sigio_to_task(struct task_struct *p,
> si.si_fd = fd;
> if (!do_send_sig_info(signum, &si, p, type))
> break;
> + }
> /* fall-through - fall back on the old plain SIGIO signal */
> case 0:
> do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, type);
>
--
Kees Cook
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] fcntl: Distribute switch variables for initialization
2020-03-03 4:41 ` Kees Cook
@ 2020-03-03 15:55 ` Jeff Layton
2020-03-03 21:11 ` Kees Cook
0 siblings, 1 reply; 4+ messages in thread
From: Jeff Layton @ 2020-03-03 15:55 UTC (permalink / raw)
To: Kees Cook, J. Bruce Fields, Jens Axboe, Al Viro
Cc: Alexander Potapenko, linux-fsdevel, linux-kernel
On Mon, 2020-03-02 at 20:41 -0800, Kees Cook wrote:
> On Wed, Feb 19, 2020 at 10:22:43PM -0800, Kees Cook wrote:
> > Variables declared in a switch statement before any case statements
> > cannot be automatically initialized with compiler instrumentation (as
> > they are not part of any execution flow). With GCC's proposed automatic
> > stack variable initialization feature, this triggers a warning (and they
> > don't get initialized). Clang's automatic stack variable initialization
> > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> > doesn't initialize such variables[1]. Note that these warnings (or silent
> > skipping) happen before the dead-store elimination optimization phase,
> > so even when the automatic initializations are later elided in favor of
> > direct initializations, the warnings remain.
> >
> > To avoid these problems, move such variables into the "case" where
> > they're used or lift them up into the main function body.
> >
> > fs/fcntl.c: In function ‘send_sigio_to_task’:
> > fs/fcntl.c:738:20: warning: statement will never be executed [-Wswitch-unreachable]
> > 738 | kernel_siginfo_t si;
> > | ^~
> >
> > [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> >
> > Signed-off-by: Kees Cook <keescook@chromium.org>
>
> Ping. Can someone pick this up, please?
>
> Thanks!
>
> -Kees
>
> > ---
> > fs/fcntl.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/fcntl.c b/fs/fcntl.c
> > index 9bc167562ee8..2e4c0fa2074b 100644
> > --- a/fs/fcntl.c
> > +++ b/fs/fcntl.c
> > @@ -735,8 +735,9 @@ static void send_sigio_to_task(struct task_struct *p,
> > return;
> >
> > switch (signum) {
> > - kernel_siginfo_t si;
> > - default:
> > + default: {
> > + kernel_siginfo_t si;
> > +
> > /* Queue a rt signal with the appropriate fd as its
> > value. We use SI_SIGIO as the source, not
> > SI_KERNEL, since kernel signals always get
> > @@ -769,6 +770,7 @@ static void send_sigio_to_task(struct task_struct *p,
> > si.si_fd = fd;
> > if (!do_send_sig_info(signum, &si, p, type))
> > break;
> > + }
> > /* fall-through - fall back on the old plain SIGIO signal */
> > case 0:
> > do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, type);
> >
Sure, looks straightforward enough. I'll pick it up for v5.7.
Thanks,
--
Jeff Layton <jlayton@kernel.org>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] fcntl: Distribute switch variables for initialization
2020-03-03 15:55 ` Jeff Layton
@ 2020-03-03 21:11 ` Kees Cook
0 siblings, 0 replies; 4+ messages in thread
From: Kees Cook @ 2020-03-03 21:11 UTC (permalink / raw)
To: Jeff Layton
Cc: J. Bruce Fields, Jens Axboe, Al Viro, Alexander Potapenko,
linux-fsdevel, linux-kernel
On Tue, Mar 03, 2020 at 10:55:22AM -0500, Jeff Layton wrote:
> On Mon, 2020-03-02 at 20:41 -0800, Kees Cook wrote:
> > On Wed, Feb 19, 2020 at 10:22:43PM -0800, Kees Cook wrote:
> > > Variables declared in a switch statement before any case statements
> > > cannot be automatically initialized with compiler instrumentation (as
> > > they are not part of any execution flow). With GCC's proposed automatic
> > > stack variable initialization feature, this triggers a warning (and they
> > > don't get initialized). Clang's automatic stack variable initialization
> > > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> > > doesn't initialize such variables[1]. Note that these warnings (or silent
> > > skipping) happen before the dead-store elimination optimization phase,
> > > so even when the automatic initializations are later elided in favor of
> > > direct initializations, the warnings remain.
> > >
> > > To avoid these problems, move such variables into the "case" where
> > > they're used or lift them up into the main function body.
> > >
> > > fs/fcntl.c: In function ‘send_sigio_to_task’:
> > > fs/fcntl.c:738:20: warning: statement will never be executed [-Wswitch-unreachable]
> > > 738 | kernel_siginfo_t si;
> > > | ^~
> > >
> > > [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> > >
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > Ping. Can someone pick this up, please?
> >
> > Thanks!
> >
> > -Kees
> >
> > > ---
> > > fs/fcntl.c | 6 ++++--
> > > 1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/fcntl.c b/fs/fcntl.c
> > > index 9bc167562ee8..2e4c0fa2074b 100644
> > > --- a/fs/fcntl.c
> > > +++ b/fs/fcntl.c
> > > @@ -735,8 +735,9 @@ static void send_sigio_to_task(struct task_struct *p,
> > > return;
> > >
> > > switch (signum) {
> > > - kernel_siginfo_t si;
> > > - default:
> > > + default: {
> > > + kernel_siginfo_t si;
> > > +
> > > /* Queue a rt signal with the appropriate fd as its
> > > value. We use SI_SIGIO as the source, not
> > > SI_KERNEL, since kernel signals always get
> > > @@ -769,6 +770,7 @@ static void send_sigio_to_task(struct task_struct *p,
> > > si.si_fd = fd;
> > > if (!do_send_sig_info(signum, &si, p, type))
> > > break;
> > > + }
> > > /* fall-through - fall back on the old plain SIGIO signal */
> > > case 0:
> > > do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, type);
> > >
>
> Sure, looks straightforward enough. I'll pick it up for v5.7.
Awesome; thank you!
-Kees
>
> Thanks,
> --
> Jeff Layton <jlayton@kernel.org>
>
--
Kees Cook
^ permalink raw reply [flat|nested] 4+ messages in thread
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