diff mbox series

fcntl: Distribute switch variables for initialization

Message ID 20200220062243.68809-1-keescook@chromium.org
State New, archived
Headers show
Series fcntl: Distribute switch variables for initialization | expand

Commit Message

Kees Cook Feb. 20, 2020, 6:22 a.m. UTC
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(-)

Comments

Kees Cook March 3, 2020, 4:41 a.m. UTC | #1
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);
>
Jeff Layton March 3, 2020, 3:55 p.m. UTC | #2
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,
Kees Cook March 3, 2020, 9:11 p.m. UTC | #3
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>
>
diff mbox series

Patch

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);