Re: [PATCH v2 1/3] vsscanf(): Integer overflow is a conversion failure

[Dan Carpenter]

On Sat, Jun 10, 2023 at 01:07:41PM -0400, Demi Marie Obenour wrote:
> ---
>  .../hive_isp_css_include/platform_support.h   |  1 -
>  include/linux/limits.h                        |  1 +
>  include/linux/mfd/wl1273-core.h               |  3 -
>  include/vdso/limits.h                         |  3 +
>  lib/vsprintf.c                                | 82 ++++++++++++++-----
>  5 files changed, 67 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/staging/media/atomisp/pci/hive_isp_css_include/platform_support.h b/drivers/staging/media/atomisp/pci/hive_isp_css_include/platform_support.h
> index 0cdef4a5e8b1bed9884133f1a0b9d853d59d43a4..e29b96d8bebf14839f6dd48fdc6c0f8b029ef31d 100644
> --- a/drivers/staging/media/atomisp/pci/hive_isp_css_include/platform_support.h
> +++ b/drivers/staging/media/atomisp/pci/hive_isp_css_include/platform_support.h
> @@ -27,7 +27,6 @@
>  
>  #define UINT16_MAX USHRT_MAX
>  #define UINT32_MAX UINT_MAX
> -#define UCHAR_MAX  (255)
>  
>  #define CSS_ALIGN(d, a) d __attribute__((aligned(a)))
>  
> 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))

It looks like you're going to have to redo these patches anyway for
various reasons.  Could you pull the U/SCHAR_MAX changes out into a
separate patch?

> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 40f560959b169b4c4ac6154d658cfe76cfd0c5a6..8caccdcda0a2b470cda70c9b3837de37207eb512 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 */

It's not clear what this FIXME is for, but probably it should go next to
the cp += (rv & ~KSTRTOX_OVERFLOW); line?  Does anyone know what it
means?  Maybe just delete it.

> +		if (overflow)
> +			*overflow = !!(rv & KSTRTOX_OVERFLOW);
>  		cp += (rv & ~KSTRTOX_OVERFLOW);
>  	} else {

*overflow isn't initialized on the else path.

>  		/* 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;
>  }
>  
>  /**
> @@ -3441,7 +3447,7 @@ 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, allow_overflow;
>  
>  	while (*fmt) {
>  		/* skip any white space in format */
> @@ -3464,6 +3470,9 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
>  			break;
>  		++fmt;
>  
> +		allow_overflow = *fmt == '!';
> +		fmt += (int)allow_overflow;
> +
>  		/* skip this conversion.
>  		 * advance both strings to next white space
>  		 */
> @@ -3649,45 +3658,80 @@ 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 && !allow_overflow))

So that means that *overflow can be uninitialized here.

> +			break;
>  
>  		switch (qualifier) {

regards,
dan carpenter