* Re: [RFC PATCH] kernel/panic: Filter out a potential trailing newline
2018-10-09 20:50 [RFC PATCH] kernel/panic: Filter out a potential trailing newline Borislav Petkov
@ 2018-10-09 21:13 ` Kees Cook
2018-10-09 21:23 ` Steven Rostedt
2018-10-10 6:00 ` Ingo Molnar
2 siblings, 0 replies; 4+ messages in thread
From: Kees Cook @ 2018-10-09 21:13 UTC (permalink / raw)
To: Borislav Petkov; +Cc: LKML, Andrew Morton, Steven Rostedt (VMware), X86 ML
On Tue, Oct 9, 2018 at 1:50 PM, Borislav Petkov <bp@alien8.de> wrote:
> From: Borislav Petkov <bp@suse.de>
>
> If a call to panic() terminates the string with a \n, the result puts
> the closing brace ']---' on a newline because panic() itself adds \n
> too.
>
> Now, if one goes and removes the newline chars from all panic()
> invocations - and the stats right now look like this:
>
> ~300 calls with an \n
> ~500 calls without a \n
>
> one is destined to a neverending game of whack-a-mole because the usual
> thing to do is add a newline at the end of a string a function is
> supposed to print.
>
> Therefore, simply zap any \n at the end of the panic string to avoid
> touching so many places in the kernel.
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> Cc: x86@kernel.org
Ah yes, I like this. :)
Acked-by: Kees Cook <keescook@chromium.org>
-Kees
> ---
> kernel/panic.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 8b2e002d52eb..5776d2879650 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -136,7 +136,7 @@ void panic(const char *fmt, ...)
> {
> static char buf[1024];
> va_list args;
> - long i, i_next = 0;
> + long i, i_next = 0, len;
> int state = 0;
> int old_cpu, this_cpu;
> bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;
> @@ -173,8 +173,12 @@ void panic(const char *fmt, ...)
> console_verbose();
> bust_spinlocks(1);
> va_start(args, fmt);
> - vsnprintf(buf, sizeof(buf), fmt, args);
> + len = vscnprintf(buf, sizeof(buf), fmt, args);
> va_end(args);
> +
> + if (len && buf[len - 1] == '\n')
> + buf[len - 1] = '\0';
> +
> pr_emerg("Kernel panic - not syncing: %s\n", buf);
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> /*
> --
> 2.19.0.271.gfe8321ec057f
>
--
Kees Cook
Pixel Security
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [RFC PATCH] kernel/panic: Filter out a potential trailing newline
2018-10-09 20:50 [RFC PATCH] kernel/panic: Filter out a potential trailing newline Borislav Petkov
2018-10-09 21:13 ` Kees Cook
@ 2018-10-09 21:23 ` Steven Rostedt
2018-10-10 6:00 ` Ingo Molnar
2 siblings, 0 replies; 4+ messages in thread
From: Steven Rostedt @ 2018-10-09 21:23 UTC (permalink / raw)
To: Borislav Petkov; +Cc: LKML, Andrew Morton, Kees Cook, x86
On Tue, 9 Oct 2018 22:50:19 +0200
Borislav Petkov <bp@alien8.de> wrote:
> From: Borislav Petkov <bp@suse.de>
>
> If a call to panic() terminates the string with a \n, the result puts
> the closing brace ']---' on a newline because panic() itself adds \n
> too.
>
> Now, if one goes and removes the newline chars from all panic()
> invocations - and the stats right now look like this:
>
> ~300 calls with an \n
> ~500 calls without a \n
>
> one is destined to a neverending game of whack-a-mole because the usual
> thing to do is add a newline at the end of a string a function is
> supposed to print.
>
> Therefore, simply zap any \n at the end of the panic string to avoid
> touching so many places in the kernel.
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> Cc: x86@kernel.org
> ---
> kernel/panic.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 8b2e002d52eb..5776d2879650 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -136,7 +136,7 @@ void panic(const char *fmt, ...)
> {
> static char buf[1024];
> va_list args;
> - long i, i_next = 0;
> + long i, i_next = 0, len;
> int state = 0;
> int old_cpu, this_cpu;
> bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;
> @@ -173,8 +173,12 @@ void panic(const char *fmt, ...)
> console_verbose();
> bust_spinlocks(1);
> va_start(args, fmt);
> - vsnprintf(buf, sizeof(buf), fmt, args);
> + len = vscnprintf(buf, sizeof(buf), fmt, args);
> va_end(args);
> +
> + if (len && buf[len - 1] == '\n')
> + buf[len - 1] = '\0';
> +
> pr_emerg("Kernel panic - not syncing: %s\n", buf);
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> /*
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [RFC PATCH] kernel/panic: Filter out a potential trailing newline
2018-10-09 20:50 [RFC PATCH] kernel/panic: Filter out a potential trailing newline Borislav Petkov
2018-10-09 21:13 ` Kees Cook
2018-10-09 21:23 ` Steven Rostedt
@ 2018-10-10 6:00 ` Ingo Molnar
2 siblings, 0 replies; 4+ messages in thread
From: Ingo Molnar @ 2018-10-10 6:00 UTC (permalink / raw)
To: Borislav Petkov
Cc: LKML, Andrew Morton, Kees Cook, Steven Rostedt (VMware), x86
* Borislav Petkov <bp@alien8.de> wrote:
> From: Borislav Petkov <bp@suse.de>
>
> If a call to panic() terminates the string with a \n, the result puts
> the closing brace ']---' on a newline because panic() itself adds \n
> too.
>
> Now, if one goes and removes the newline chars from all panic()
> invocations - and the stats right now look like this:
>
> ~300 calls with an \n
> ~500 calls without a \n
>
> one is destined to a neverending game of whack-a-mole because the usual
> thing to do is add a newline at the end of a string a function is
> supposed to print.
>
> Therefore, simply zap any \n at the end of the panic string to avoid
> touching so many places in the kernel.
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> Cc: x86@kernel.org
> ---
> kernel/panic.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 8b2e002d52eb..5776d2879650 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -136,7 +136,7 @@ void panic(const char *fmt, ...)
> {
> static char buf[1024];
> va_list args;
> - long i, i_next = 0;
> + long i, i_next = 0, len;
> int state = 0;
> int old_cpu, this_cpu;
> bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;
> @@ -173,8 +173,12 @@ void panic(const char *fmt, ...)
> console_verbose();
> bust_spinlocks(1);
> va_start(args, fmt);
> - vsnprintf(buf, sizeof(buf), fmt, args);
> + len = vscnprintf(buf, sizeof(buf), fmt, args);
> va_end(args);
> +
> + if (len && buf[len - 1] == '\n')
> + buf[len - 1] = '\0';
Nice, this patch saves a couple of hundred trivial upstream commits in the next 20 years:
Acked-by: Ingo Molnar <mingo@kernel.org>
Thanks,
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread