[U-Boot] [PATCH 2/4] Add safe vsnprintf and snprintf library functions

Simon Glass
2011-09-23T17:38:50Z

From: Sonny Rao <sonnyrao@chromium.org>

From: Sonny Rao <sonnyrao@chromium.org>

These functions are useful in U-Boot because they allow a graceful failure
rather than an unpredictable stack overflow when printf() buffers are
exceeded.

Mostly copied from the Linux kernel. I copied vscnprintf and
scnprintf so we can change printf and vprintf to use the safe
implementation but still return the correct values.

Signed-off-by: Simon Glass <sjg@chromium.org>
---
include/common.h | 8 ++-
lib/vsprintf.c | 316 ++++++++++++++++++++++++++++++++++++++++++------------
2 files changed, 256 insertions(+), 68 deletions(-)

diff --git a/include/common.h b/include/common.h
index d244bd4..fbcc55f 100644
--- a/include/common.h
+++ b/include/common.h
@@ -682,9 +682,15 @@ unsigned long long simple_strtoull(const char *cp,char **endp,unsigned int base)
long simple_strtol(const char *cp,char **endp,unsigned int base);
void panic(const char *fmt, ...)
__attribute__ ((format (__printf__, 1, 2), noreturn));
-int sprintf(char * buf, const char *fmt, ...)
+int sprintf(char *buf, const char *fmt, ...)
__attribute__ ((format (__printf__, 2, 3)));
+int snprintf(char *buf, size_t size, const char *fmt, ...)
+ __attribute__ ((format (__printf__, 3, 4)));
+int scnprintf(char *buf, size_t size, const char *fmt, ...)
+ __attribute__ ((format (__printf__, 3, 4)));
int vsprintf(char *buf, const char *fmt, va_list args);
+int vsnprintf(char *buf, size_t size, const char *fmt, va_list args);
+int vscnprintf(char *buf, size_t size, const char *fmt, va_list args);

/* lib/strmhz.c */
char * strmhz(char *buf, unsigned long hz);
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 79dead3..bac6f30 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -16,6 +16,7 @@
#include <errno.h>

#include <common.h>
+#include <limits.h>
#if !defined (CONFIG_PANIC_HANG)
#include <command.h>
#endif
@@ -289,7 +290,8 @@ static noinline char* put_dec(char *buf, unsigned NUM_TYPE num)
#define SMALL 32 /* Must be 32 == 0x20 */
#define SPECIAL 64 /* 0x */

-static char *number(char *buf, unsigned NUM_TYPE num, int base, int size, int precision, int type)
+static char *number(char *buf, char *end, unsigned NUM_TYPE num,
+ int base, int size, int precision, int type)
{
/* we are called with base 8, 10 or 16, only, thus don't need "G..." */
static const char digits[16] = "0123456789ABCDEF"; /* "GHIJKLMNOPQRSTUVWXYZ"; */
@@ -351,37 +353,63 @@ static char *number(char *buf, unsigned NUM_TYPE num, int base, int size, int pr
precision = i;
/* leading space padding */
size -= precision;
- if (!(type & (ZEROPAD+LEFT)))
- while(--size >= 0)
- *buf++ = ' ';
+ if (!(type & (ZEROPAD+LEFT))) {
+ while (--size >= 0) {
+ if (buf < end)
+ *buf = ' ';
+ ++buf;
+ }
+ }
/* sign */
- if (sign)
- *buf++ = sign;
+ if (sign) {
+ if (buf < end)
+ *buf = sign;
+ ++buf;
+ }
/* "0x" / "0" prefix */
if (need_pfx) {
- *buf++ = '0';
- if (base == 16)
- *buf++ = ('X' | locase);
+ if (buf < end)
+ *buf = '0';
+ ++buf;
+ if (base == 16) {
+ if (buf < end)
+ *buf = ('X' | locase);
+ ++buf;
+ }
}
/* zero or space padding */
if (!(type & LEFT)) {
char c = (type & ZEROPAD) ? '0' : ' ';
- while (--size >= 0)
- *buf++ = c;
+ while (--size >= 0) {
+ if (buf < end)
+ *buf = c;
+ ++buf;
+ }
}
/* hmm even more zero padding? */
- while (i <= --precision)
- *buf++ = '0';
+ while (i <= --precision) {
+ if (buf < end)
+ *buf = '0';
+ ++buf;
+ }
/* actual digits of result */
- while (--i >= 0)
- *buf++ = tmp[i];
+ while (--i >= 0) {
+ if (buf < end)
+ *buf = tmp[i];
+ ++buf;
+
+ }
/* trailing space padding */
- while (--size >= 0)
- *buf++ = ' ';
+ while (--size >= 0) {
+ if (buf < end)
+ *buf = ' ';
+ ++buf;
+ }
return buf;
}

-static char *string(char *buf, char *s, int field_width, int precision, int flags)
+static char *string(char *buf, char *end, char *s, int field_width,
+ int precision, int flags)
{
int len, i;

@@ -391,17 +419,26 @@ static char *string(char *buf, char *s, int field_width, int precision, int flag
len = strnlen(s, precision);

if (!(flags & LEFT))
- while (len < field_width--)
- *buf++ = ' ';
- for (i = 0; i < len; ++i)
- *buf++ = *s++;
- while (len < field_width--)
- *buf++ = ' ';
+ while (len < field_width--) {
+ if (buf < end)
+ *buf = ' ';
+ ++buf;
+ }
+ for (i = 0; i < len; ++i) {
+ if (buf < end)
+ *buf = *s++;
+ ++buf;
+ }
+ while (len < field_width--) {
+ if (buf < end)
+ *buf = ' ';
+ ++buf;
+ }
return buf;
}

#ifdef CONFIG_CMD_NET
-static char *mac_address_string(char *buf, u8 *addr, int field_width,
+static char *mac_address_string(char *buf, char *end, u8 *addr, int field_width,
int precision, int flags)
{
char mac_addr[6 * 3]; /* (6 * 2 hex digits), 5 colons and trailing zero */
@@ -415,10 +452,11 @@ static char *mac_address_string(char *buf, u8 *addr, int field_width,
}
*p = '\0';

- return string(buf, mac_addr, field_width, precision, flags & ~SPECIAL);
+ return string(buf, end, mac_addr, field_width, precision,
+ flags & ~SPECIAL);
}

-static char *ip6_addr_string(char *buf, u8 *addr, int field_width,
+static char *ip6_addr_string(char *buf, char *end, u8 *addr, int field_width,
int precision, int flags)
{
char ip6_addr[8 * 5]; /* (8 * 4 hex digits), 7 colons and trailing zero */
@@ -433,10 +471,11 @@ static char *ip6_addr_string(char *buf, u8 *addr, int field_width,
}
*p = '\0';

- return string(buf, ip6_addr, field_width, precision, flags & ~SPECIAL);
+ return string(buf, end, ip6_addr, field_width, precision,
+ flags & ~SPECIAL);
}

-static char *ip4_addr_string(char *buf, u8 *addr, int field_width,
+static char *ip4_addr_string(char *buf, char *end, u8 *addr, int field_width,
int precision, int flags)
{
char ip4_addr[4 * 4]; /* (4 * 3 decimal digits), 3 dots and trailing zero */
@@ -454,7 +493,8 @@ static char *ip4_addr_string(char *buf, u8 *addr, int field_width,
}
*p = '\0';

- return string(buf, ip4_addr, field_width, precision, flags & ~SPECIAL);
+ return string(buf, end, ip4_addr, field_width, precision,
+ flags & ~SPECIAL);
}
#endif

@@ -476,10 +516,12 @@ static char *ip4_addr_string(char *buf, u8 *addr, int field_width,
* function pointers are really function descriptors, which contain a
* pointer to the real address.
*/
-static char *pointer(const char *fmt, char *buf, void *ptr, int field_width, int precision, int flags)
+static char *pointer(const char *fmt, char *buf, char *end, void *ptr,
+ int field_width, int precision, int flags)
{
if (!ptr)
- return string(buf, "(null)", field_width, precision, flags);
+ return string(buf, end, "(null)", field_width, precision,
+ flags);

#ifdef CONFIG_CMD_NET
switch (*fmt) {
@@ -487,15 +529,18 @@ static char *pointer(const char *fmt, char *buf, void *ptr, int field_width, int
flags |= SPECIAL;
/* Fallthrough */
case 'M':
- return mac_address_string(buf, ptr, field_width, precision, flags);
+ return mac_address_string(buf, end, ptr, field_width,
+ precision, flags);
case 'i':
flags |= SPECIAL;
/* Fallthrough */
case 'I':
if (fmt[1] == '6')
- return ip6_addr_string(buf, ptr, field_width, precision, flags);
+ return ip6_addr_string(buf, end, ptr, field_width,
+ precision, flags);
if (fmt[1] == '4')
- return ip4_addr_string(buf, ptr, field_width, precision, flags);
+ return ip4_addr_string(buf, end, ptr, field_width,
+ precision, flags);
flags &= ~SPECIAL;
break;
}
@@ -505,31 +550,35 @@ static char *pointer(const char *fmt, char *buf, void *ptr, int field_width, int
field_width = 2*sizeof(void *);
flags |= ZEROPAD;
}
- return number(buf, (unsigned long) ptr, 16, field_width, precision, flags);
+ return number(buf, end, (unsigned long)ptr, 16, field_width,
+ precision, flags);
}

/**
- * vsprintf - Format a string and place it in a buffer
- * @buf: The buffer to place the result into
- * @fmt: The format string to use
- * @args: Arguments for the format string
+ * Format a string and place it in a buffer (base function)
*
- * This function follows C99 vsprintf, but has some extensions:
+ * @param buf The buffer to place the result into
+ * @param size The size of the buffer, including the trailing null space
+ * @param fmt The format string to use
+ * @param args Arguments for the format string
+ *
+ * This function follows C99 vsnprintf, but has some extensions:
* %pS output the name of a text symbol
* %pF output the name of a function pointer
* %pR output the address range in a struct resource
*
- * The function returns the number of characters written
- * into @buf.
+ * The function returns the number of characters which would be
+ * generated for the given input, excluding the trailing '\0',
+ * as per ISO C99.
*
* Call this function if you are already dealing with a va_list.
- * You probably want sprintf() instead.
+ * You probably want snprintf() instead.
*/
-int vsprintf(char *buf, const char *fmt, va_list args)
+int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
{
unsigned NUM_TYPE num;
int base;
- char *str;
+ char *str, *end;

int flags; /* flags to number() */

@@ -542,10 +591,19 @@ int vsprintf(char *buf, const char *fmt, va_list args)
/* 't' added for ptrdiff_t */

str = buf;
+ end = str + size;
+
+ /* Make sure end is always >= buf */
+ if (end < buf) {
+ end = ((void *)-1);
+ size = end - buf;
+ }

for (; *fmt ; ++fmt) {
if (*fmt != '%') {
- *str++ = *fmt;
+ if (str < end)
+ *str = *fmt;
+ ++str;
continue;
}

@@ -606,21 +664,32 @@ int vsprintf(char *buf, const char *fmt, va_list args)
base = 10;

switch (*fmt) {
- case 'c':
+ case 'c': {
+ char c;
if (!(flags & LEFT))
- while (--field_width > 0)
- *str++ = ' ';
- *str++ = (unsigned char) va_arg(args, int);
- while (--field_width > 0)
- *str++ = ' ';
+ while (--field_width > 0) {
+ if (str < end)
+ *str = ' ';
+ ++str;
+ }
+ c = (unsigned char) va_arg(args, int);
+ if (str < end)
+ *str = c;
+ ++str;
+ while (--field_width > 0) {
+ if (str < end)
+ *str = ' ';
+ ++str;
+ }
continue;
-
+ }
case 's':
- str = string(str, va_arg(args, char *), field_width, precision, flags);
+ str = string(str, end, va_arg(args, char *),
+ field_width, precision, flags);
continue;

case 'p':
- str = pointer(fmt+1, str,
+ str = pointer(fmt+1, str, end,
va_arg(args, void *),
field_width, precision, flags);
/* Skip all alphanumeric pointer suffixes */
@@ -639,7 +708,9 @@ int vsprintf(char *buf, const char *fmt, va_list args)
continue;

case '%':
- *str++ = '%';
+ if (str < end)
+ *str = '%';
+ ++str;
continue;

/* integer number formats - set up the flags and "break" */
@@ -660,10 +731,14 @@ int vsprintf(char *buf, const char *fmt, va_list args)
break;

default:
- *str++ = '%';
- if (*fmt)
- *str++ = *fmt;
- else
+ if (str < end)
+ *str = '%';
+ ++str;
+ if (*fmt) {
+ if (str < end)
+ *str = *fmt;
+ ++str;
+ } else
--fmt;
continue;
}
@@ -686,17 +761,124 @@ int vsprintf(char *buf, const char *fmt, va_list args)
if (flags & SIGN)
num = (signed int) num;
}
- str = number(str, num, base, field_width, precision, flags);
+ str = number(str, end, num, base, field_width, precision,
+ flags);
+ }
+
+ if (size > 0) {
+ if (str < end)
+ *str = '\0';
+ else
+ end[-1] = '\0';
}
- *str = '\0';
+ /* the trailing null byte doesn't count towards the total */
return str-buf;
}

/**
- * sprintf - Format a string and place it in a buffer
- * @buf: The buffer to place the result into
- * @fmt: The format string to use
- * @...: Arguments for the format string
+ * Format a string and place it in a buffer (va_list version)
+ *
+ * @param buf The buffer to place the result into
+ * @param size The size of the buffer, including the trailing null space
+ * @param fmt The format string to use
+ * @param args Arguments for the format string
+ * @return the number of characters which have been written into
+ * the @buf not including the trailing '\0'. If @size is == 0 the function
+ * returns 0.
+ *
+ * If you're not already dealing with a va_list consider using scnprintf().
+ *
+ * See the vsprintf() documentation for format string extensions over C99.
+ */
+int vscnprintf(char *buf, size_t size, const char *fmt, va_list args)
+{
+ int i;
+
+ i = vsnprintf(buf, size, fmt, args);
+
+ if (likely(i < size))
+ return i;
+ if (size != 0)
+ return size - 1;
+ return 0;
+}
+
+/**
+ * Format a string and place it in a buffer
+ *
+ * @param buf The buffer to place the result into
+ * @param size The size of the buffer, including the trailing null space
+ * @param fmt The format string to use
+ * @param ... Arguments for the format string
+ * @return the number of characters which would be
+ * generated for the given input, excluding the trailing null,
+ * as per ISO C99. If the return is greater than or equal to
+ * @size, the resulting string is truncated.
+ *
+ * See the vsprintf() documentation for format string extensions over C99.
+ */
+int snprintf(char *buf, size_t size, const char *fmt, ...)
+{
+ va_list args;
+ int i;
+
+ va_start(args, fmt);
+ i = vsnprintf(buf, size, fmt, args);
+ va_end(args);
+
+ return i;
+}
+
+/**
+ * Format a string and place it in a buffer
+ *
+ * @param buf The buffer to place the result into
+ * @param size The size of the buffer, including the trailing null space
+ * @param fmt The format string to use
+ * @param ... Arguments for the format string
+ *
+ * The return value is the number of characters written into @buf not including
+ * the trailing '\0'. If @size is == 0 the function returns 0.
+ *
+ * See the vsprintf() documentation for format string extensions over C99.
+ */
+
+int scnprintf(char *buf, size_t size, const char *fmt, ...)
+{
+ va_list args;
+ int i;
+
+ va_start(args, fmt);
+ i = vscnprintf(buf, size, fmt, args);
+ va_end(args);
+
+ return i;
+}
+
+/**
+ * Format a string and place it in a buffer (va_list version)
+ *
+ * @param buf The buffer to place the result into
+ * @param fmt The format string to use
+ * @param args Arguments for the format string
+ *
+ * The function returns the number of characters written
+ * into @buf. Use vsnprintf() or vscnprintf() in order to avoid
+ * buffer overflows.
+ *
+ * If you're not already dealing with a va_list consider using sprintf().
+ */
+int vsprintf(char *buf, const char *fmt, va_list args)
+{
+ return vsnprintf(buf, INT_MAX, fmt, args);
+}
+
+/**
+ * Format a string and place it in a buffer
+ *
+ * @param buf The buffer to place the result into
+ * @param fmt The format string to use
+ * @param ... Arguments for the format string
*
* The function returns the number of characters written
* into @buf.
--
1.7.3.1