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Message-ID: <ZIQrevjNjMn9cBRM@infradead.org>
Date: Sat, 10 Jun 2023 00:51:22 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Demi Marie Obenour <demi@...isiblethingslab.com>,
Richard Weinberger <richard@....at>,
Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Dwaipayan Ray <dwaipayanray1@...il.com>,
Lukas Bulwahn <lukas.bulwahn@...il.com>,
Joe Perches <joe@...ches.com>,
Jonathan Corbet <corbet@....net>,
Federico Vaga <federico.vaga@...a.pv.it>,
Juergen Gross <jgross@...e.com>,
Stefano Stabellini <sstabellini@...nel.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Lee Jones <lee@...nel.org>, Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vincenzo Frascino <vincenzo.frascino@....com>,
Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 2/4] vsscanf(): Return -ERANGE on integer overflow
[Adding Richard and Linus as they're having another overflow checking
discussion and we should probably merge those]
On Fri, Jun 09, 2023 at 10:57:57PM -0400, Demi Marie Obenour wrote:
> Userspace sets errno to ERANGE, but the kernel can't do that.
That seems like a very parse commit log, and also kinda besides
the point - the kernel always returns error in-line and not through
errno. I think you need to document here why we want to do the
overflow checking (not that I doubt it, but it really needs to be
in the commit message).
Leaving the rest of the quote here for the new arrivals.
>
> Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>
> ---
> include/linux/limits.h | 1 +
> include/linux/mfd/wl1273-core.h | 3 --
> include/vdso/limits.h | 3 ++
> lib/vsprintf.c | 80 ++++++++++++++++++++++++---------
> 4 files changed, 63 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/limits.h b/include/linux/limits.h
> index f6bcc936901071f496e3e85bb6e1d93905b12e32..8f7fd85b41fb46e6992d9e5912da00424119227a 100644
> --- a/include/linux/limits.h
> +++ b/include/linux/limits.h
> @@ -8,6 +8,7 @@
>
> #define SIZE_MAX (~(size_t)0)
> #define SSIZE_MAX ((ssize_t)(SIZE_MAX >> 1))
> +#define SSIZE_MIN (-SSIZE_MAX - 1)
> #define PHYS_ADDR_MAX (~(phys_addr_t)0)
>
> #define U8_MAX ((u8)~0U)
> diff --git a/include/linux/mfd/wl1273-core.h b/include/linux/mfd/wl1273-core.h
> index c28cf76d5c31ee1c94a9319a2e2d318bf00283a6..b81a229135ed9f756c749122a8341816031c8311 100644
> --- a/include/linux/mfd/wl1273-core.h
> +++ b/include/linux/mfd/wl1273-core.h
> @@ -204,9 +204,6 @@
> WL1273_IS2_TRI_OPT | \
> WL1273_IS2_RATE_48K)
>
> -#define SCHAR_MIN (-128)
> -#define SCHAR_MAX 127
> -
> #define WL1273_FR_EVENT BIT(0)
> #define WL1273_BL_EVENT BIT(1)
> #define WL1273_RDS_EVENT BIT(2)
> diff --git a/include/vdso/limits.h b/include/vdso/limits.h
> index 0197888ad0e00b2f853d3f25ffa764f61cca7385..0cad0a2490e5efc194d874025eb3e3b846a5c7b4 100644
> --- a/include/vdso/limits.h
> +++ b/include/vdso/limits.h
> @@ -2,6 +2,9 @@
> #ifndef __VDSO_LIMITS_H
> #define __VDSO_LIMITS_H
>
> +#define UCHAR_MAX ((unsigned char)~0U)
> +#define SCHAR_MAX ((signed char)(UCHAR_MAX >> 1))
> +#define SCHAR_MIN ((signed char)(-SCHAR_MAX - 1))
> #define USHRT_MAX ((unsigned short)~0U)
> #define SHRT_MAX ((short)(USHRT_MAX >> 1))
> #define SHRT_MIN ((short)(-SHRT_MAX - 1))
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index a60d348efb276d66ca07fe464883408df7fdab97..9846d2385f5b9e8f3945a5664d81047e97cf10d5 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -59,7 +59,7 @@
> bool no_hash_pointers __ro_after_init;
> EXPORT_SYMBOL_GPL(no_hash_pointers);
>
> -static noinline unsigned long long simple_strntoull(const char *startp, size_t max_chars, char **endp, unsigned int base)
> +static noinline unsigned long long simple_strntoull(const char *startp, size_t max_chars, char **endp, unsigned int base, bool *overflow)
> {
> const char *cp;
> unsigned long long result = 0ULL;
> @@ -71,6 +71,8 @@ static noinline unsigned long long simple_strntoull(const char *startp, size_t m
> if (prefix_chars < max_chars) {
> rv = _parse_integer_limit(cp, base, &result, max_chars - prefix_chars);
> /* FIXME */
> + if (overflow)
> + *overflow = !!(rv & KSTRTOX_OVERFLOW);
> cp += (rv & ~KSTRTOX_OVERFLOW);
> } else {
> /* Field too short for prefix + digit, skip over without converting */
> @@ -94,7 +96,7 @@ static noinline unsigned long long simple_strntoull(const char *startp, size_t m
> noinline
> unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)
> {
> - return simple_strntoull(cp, INT_MAX, endp, base);
> + return simple_strntoull(cp, INT_MAX, endp, base, NULL);
> }
> EXPORT_SYMBOL(simple_strtoull);
>
> @@ -130,18 +132,22 @@ long simple_strtol(const char *cp, char **endp, unsigned int base)
> EXPORT_SYMBOL(simple_strtol);
>
> static long long simple_strntoll(const char *cp, size_t max_chars, char **endp,
> - unsigned int base)
> + unsigned int base, bool *overflow)
> {
> + unsigned long long minand;
> + bool negate;
> +
> /*
> * simple_strntoull() safely handles receiving max_chars==0 in the
> * case cp[0] == '-' && max_chars == 1.
> * If max_chars == 0 we can drop through and pass it to simple_strntoull()
> * and the content of *cp is irrelevant.
> */
> - if (*cp == '-' && max_chars > 0)
> - return -simple_strntoull(cp + 1, max_chars - 1, endp, base);
> -
> - return simple_strntoull(cp, max_chars, endp, base);
> + negate = *cp == '-' && max_chars > 0;
> + minand = simple_strntoull(cp + negate, max_chars - negate, endp, base, overflow);
> + if (minand > (unsigned long long)LONG_MAX + negate)
> + *overflow = true;
> + return negate ? -minand : minand;
> }
>
> static noinline_for_stack
> @@ -3427,7 +3433,7 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
> unsigned long long u;
> } val;
> s16 field_width;
> - bool is_sign;
> + bool is_sign, overflow;
>
> while (*fmt) {
> /* skip any white space in format */
> @@ -3635,45 +3641,77 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
> if (is_sign)
> val.s = simple_strntoll(str,
> field_width >= 0 ? field_width : INT_MAX,
> - &next, base);
> + &next, base, &overflow);
> else
> val.u = simple_strntoull(str,
> field_width >= 0 ? field_width : INT_MAX,
> - &next, base);
> + &next, base, &overflow);
> + if (unlikely(overflow))
> + return -ERANGE;
>
> switch (qualifier) {
> case 'H': /* that's 'hh' in format */
> - if (is_sign)
> + if (is_sign) {
> + if (unlikely(val.s < SCHAR_MIN || val.s > SCHAR_MAX))
> + return -ERANGE;
> *va_arg(args, signed char *) = val.s;
> - else
> + } else {
> + if (unlikely(val.u > UCHAR_MAX))
> + return -ERANGE;
> *va_arg(args, unsigned char *) = val.u;
> + }
> break;
> case 'h':
> - if (is_sign)
> + if (is_sign) {
> + if (unlikely(val.s < SHRT_MIN || val.s > SHRT_MAX))
> + return -ERANGE;
> *va_arg(args, short *) = val.s;
> - else
> + } else {
> + if (unlikely(val.u > USHRT_MAX))
> + return -ERANGE;
> *va_arg(args, unsigned short *) = val.u;
> + }
> break;
> case 'l':
> - if (is_sign)
> + if (is_sign) {
> + if (unlikely(val.s < LONG_MIN || val.s > LONG_MAX))
> + return -ERANGE;
> *va_arg(args, long *) = val.s;
> - else
> + } else {
> + if (unlikely(val.u > ULONG_MAX))
> + return -ERANGE;
> *va_arg(args, unsigned long *) = val.u;
> + }
> break;
> case 'L':
> - if (is_sign)
> + /* No overflow check needed */
> + if (is_sign) {
> *va_arg(args, long long *) = val.s;
> - else
> + } else {
> *va_arg(args, unsigned long long *) = val.u;
> + }
> break;
> case 'z':
> - *va_arg(args, size_t *) = val.u;
> + if (is_sign) {
> + if (unlikely(val.s < SSIZE_MIN || val.s > SSIZE_MAX))
> + return -ERANGE;
> + *va_arg(args, ssize_t *) = val.s;
> + } else {
> + if (unlikely(val.u > SIZE_MAX))
> + return -ERANGE;
> + *va_arg(args, size_t *) = val.u;
> + }
> break;
> default:
> - if (is_sign)
> + if (is_sign) {
> + if (unlikely(val.s < INT_MIN || val.s > INT_MAX))
> + return -ERANGE;
> *va_arg(args, int *) = val.s;
> - else
> + } else {
> + if (unlikely(val.u > UINT_MAX))
> + return -ERANGE;
> *va_arg(args, unsigned int *) = val.u;
> + }
> break;
> }
> num++;
> --
> Sincerely,
> Demi Marie Obenour (she/her/hers)
> Invisible Things Lab
>
---end quoted text---
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