Date: Sun, 22 Mar 2015 13:38:22 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Tiwei Bie <btw@mail.ustc.edu.cn> Cc: freebsd-hackers@freebsd.org, Mateusz Guzik <mjguzik@gmail.com> Subject: Re: [PATCH] Finish the task 'Validate coredump format string' Message-ID: <20150322113822.GB2379@kib.kiev.ua> In-Reply-To: <20150322112555.GA44277@freebsd> References: <1426946345-67889-1-git-send-email-btw@mail.ustc.edu.cn> <20150321200500.GC14650@dft-labs.eu> <20150322091853.GA89976@freebsd> <20150322101401.GH14650@dft-labs.eu> <20150322112555.GA44277@freebsd>
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On Sun, Mar 22, 2015 at 07:25:55PM +0800, Tiwei Bie wrote:
> On Sun, Mar 22, 2015 at 11:14:01AM +0100, Mateusz Guzik wrote:
> > On Sun, Mar 22, 2015 at 05:19:40PM +0800, Tiwei Bie wrote:
> [..]
> >
> > A dedicated sysinit func could fetch and validate the tunable, if any.
> > If no tunable was provided it would alloc memory for the default.
> >
>
> My new patch, that uses a dedicated sysinit func to fetch and validate
> the tunable:
>
> ---
> sys/kern/kern_sig.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 59 insertions(+), 1 deletion(-)
>
> diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
> index 8410d9d..e2a00ba 100644
> --- a/sys/kern/kern_sig.c
> +++ b/sys/kern/kern_sig.c
> @@ -3096,19 +3096,77 @@ static int compress_user_cores = 0;
>
> static char corefilename[MAXPATHLEN] = {"%N.core"};
Are {} around string literal needed ?
>
> +static bool
> +corefilename_check(const char *format)
> +{
> + int i, counti;
> +
> + counti = 0;
> + for (i = 0; format[i] != '\0'; i++) {
> + if (format[i] == '%') {
> + i++;
> + switch (format[i]) {
> + case 'I':
> + counti++;
> + if (counti > 1) {
> + printf("Too many index flags specified "
> + "in corename `%s'\n", format);
I very much dislike the kernel lecturing the user about things.
Kernel must silently return an error code, with man pages providing
explanation of errors.
> + return (false);
> + }
> + case '%':
> + case 'H':
> + case 'N':
> + case 'P':
> + case 'U':
> + break;
> + default:
> + printf("Unknown format character %c in "
> + "corename `%s'\n", format[i], format);
Same there.
> + return (false);
> + }
> + }
> + }
> +
> + return (true);
> +}
> +
> +static void
> +corefilename_init(void *arg)
> +{
> + char *format = kern_getenv("kern.corefile");
Do not use initialization at the local variable declaration. It is
a requirement of style(9).
> +
> + if (format != NULL && corefilename_check(format))
> + strncpy(corefilename, format, sizeof(corefilename));
Use of strncpy() is almost always an indication of the bug. Is it acceptable
for corefilename be non-null terminated ?
> +}
> +SYSINIT(corefilename, SI_SUB_KMEM, SI_ORDER_FIRST, corefilename_init, 0);
> +
> static int
> sysctl_kern_corefile(SYSCTL_HANDLER_ARGS)
> {
> + char *format;
> int error;
>
> + format = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
> +
> + sx_slock(&corefilename_lock);
> + strncpy(format, corefilename, MAXPATHLEN);
> + sx_sunlock(&corefilename_lock);
> +
> + error = sysctl_handle_string(oidp, format, MAXPATHLEN, req);
> + if (error != 0 || strcmp(format, corefilename) == 0 ||
> + !corefilename_check(format))
> + goto out;
This code somehow misses the check for req->newptr. Did you verified
that simply fetching current value for kern.corefile works after the
patch ?
> +
> sx_xlock(&corefilename_lock);
> error = sysctl_handle_string(oidp, corefilename, sizeof(corefilename),
> req);
> sx_xunlock(&corefilename_lock);
>
> +out:
> + free(format, M_TEMP);
> return (error);
> }
> -SYSCTL_PROC(_kern, OID_AUTO, corefile, CTLTYPE_STRING | CTLFLAG_RWTUN |
> +SYSCTL_PROC(_kern, OID_AUTO, corefile, CTLTYPE_STRING | CTLFLAG_RW |
> CTLFLAG_MPSAFE, 0, 0, sysctl_kern_corefile, "A",
> "Process corefile name format string");
>
> --
> 2.1.2
>
> Best regards,
> Tiwei Bie
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