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Subject[PATCH] Add error check to hex2bin().
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Currently, security/keys/ is the only user of hex2bin().
Should I keep hex2bin() unmodified in case of bad input?
If so, I'd like to make it as hex2bin_safe().
----------------------------------------
[PATCH] Add error check to hex2bin().
Since converting 2 hexadecimal letters into a byte with error checks is
commonly used, we can replace multiple hex_to_bin() calls with single hex2bin()
call by changing hex2bin() to do error checks.

Signed-off-by: Tetsuo Handa <penguin-kernel@I=love.SAKURA.ne.jp>
---
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 953352a..186e9fc 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -374,7 +374,7 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
}

extern int hex_to_bin(char ch);
-extern void hex2bin(u8 *dst, const char *src, size_t count);
+extern bool hex2bin(u8 *dst, const char *src, size_t count);

/*
* General tracing related utility functions - trace_printk(),
diff --git a/lib/hexdump.c b/lib/hexdump.c
index f5fe6ba..1524002 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -38,14 +38,22 @@ EXPORT_SYMBOL(hex_to_bin);
* @dst: binary result
* @src: ascii hexadecimal string
* @count: result length
+ *
+ * Returns true on success, false in case of bad input.
*/
-void hex2bin(u8 *dst, const char *src, size_t count)
+bool hex2bin(u8 *dst, const char *src, size_t count)
{
while (count--) {
- *dst = hex_to_bin(*src++) << 4;
- *dst += hex_to_bin(*src++);
- dst++;
+ int c = hex_to_bin(*src++);
+ int d;
+ if (c < 0)
+ return false;
+ d = hex_to_bin(*src++);
+ if (d < 0)
+ return false;
+ *dst++ = (c << 4) | d;
}
+ return true;
}
EXPORT_SYMBOL(hex2bin);


In message "Re: [PATCH] net: can: remove custom hex_to_bin()",
Andy Shevchenko wrote:
> On Mon, 2011-07-18 at 20:41 +0900, Tetsuo Handa wrote:
> > Andy Shevchenko wrote:
> > > for (i = 0, dlc_pos++; i < cf.can_dlc; i++) {
> > > -
> > > - tmp = asc2nibble(sl->rbuff[dlc_pos++]);
> > > - if (tmp > 0x0F)
> > > + tmp = hex_to_bin(sl->rbuff[dlc_pos++]);
> > > + if (tmp < 0)
> > > return;
> > > cf.data[i] = (tmp << 4);
> > > - tmp = asc2nibble(sl->rbuff[dlc_pos++]);
> > > - if (tmp > 0x0F)
> > > + tmp = hex_to_bin(sl->rbuff[dlc_pos++]);
> > > + if (tmp < 0)
> > > return;
> > > cf.data[i] |= tmp;
> > > }
> >
> > What about changing
> >
> > void hex2bin(u8 *dst, const char *src, size_t count)
> >
> > to
> >
> > bool hex2bin(u8 *dst, const char *src, size_t count)
> >
> > in order to do error checks like
> >
> > bool hex2bin_with_validation(u8 *dst, const char *src, size_t count)
> > {
> > while (count--) {
> > int c = hex_to_bin(*src++);
> > int d;
> > if (c < 0)
> > return false;
> > d = hex_to_bin(*src++)
> > if (d < 0)
> > return false;
> > *dst++ = (c << 4) | d;
> > }
> > return true;
> > }
> >
> > and use hex2bin() rather than hex_to_bin()?
> Perhaps, good idea. Could you submit a patch?
>
> --
> Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Intel Finland Oy


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