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[Backport v2.1] net: coap: Fix possible overflow #24535

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merged 2 commits into from
May 5, 2020
Merged

[Backport v2.1] net: coap: Fix possible overflow #24535

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effce3c
math: extras: Add overflow functions to u16
Apr 17, 2020
e50bcd7
net: coap: Fix possible overflow
Apr 17, 2020
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2 changes: 2 additions & 0 deletions include/sys/math_extras.h
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
* true if the operation overflowed.
*/
/**@{*/
static bool u16_add_overflow(u16_t a, u16_t b, u16_t *result);
static bool u32_add_overflow(u32_t a, u32_t b, u32_t *result);
static bool u64_add_overflow(u64_t a, u64_t b, u64_t *result);
static bool size_add_overflow(size_t a, size_t b, size_t *result);
Expand All @@ -40,6 +41,7 @@ static bool size_add_overflow(size_t a, size_t b, size_t *result);
* true if the operation overflowed.
*/
/**@{*/
static bool u16_mul_overflow(u16_t a, u16_t b, u16_t *result);
static bool u32_mul_overflow(u32_t a, u32_t b, u32_t *result);
static bool u64_mul_overflow(u64_t a, u64_t b, u64_t *result);
static bool size_mul_overflow(size_t a, size_t b, size_t *result);
Expand Down
28 changes: 28 additions & 0 deletions include/sys/math_extras_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,11 @@
#endif

#if use_builtin(__builtin_add_overflow)
static inline bool u16_add_overflow(u16_t a, u16_t b, u16_t *result)
{
return __builtin_add_overflow(a, b, result);
}

static inline bool u32_add_overflow(u32_t a, u32_t b, u32_t *result)
{
return __builtin_add_overflow(a, b, result);
Expand All @@ -44,6 +49,15 @@ static inline bool size_add_overflow(size_t a, size_t b, size_t *result)
return __builtin_add_overflow(a, b, result);
}
#else /* !use_builtin(__builtin_add_overflow) */
static inline bool u16_add_overflow(u16_t a, u16_t b, u16_t *result)
{
u16_t c = a + b;

*result = c;

return c < a;
}

static inline bool u32_add_overflow(u32_t a, u32_t b, u32_t *result)
{
u32_t c = a + b;
Expand Down Expand Up @@ -73,6 +87,11 @@ static inline bool size_add_overflow(size_t a, size_t b, size_t *result)
#endif /* use_builtin(__builtin_add_overflow) */

#if use_builtin(__builtin_mul_overflow)
static inline bool u16_mul_overflow(u16_t a, u16_t b, u16_t *result)
{
return __builtin_mul_overflow(a, b, result);
}

static inline bool u32_mul_overflow(u32_t a, u32_t b, u32_t *result)
{
return __builtin_mul_overflow(a, b, result);
Expand All @@ -88,6 +107,15 @@ static inline bool size_mul_overflow(size_t a, size_t b, size_t *result)
return __builtin_mul_overflow(a, b, result);
}
#else /* !use_builtin(__builtin_mul_overflow) */
static inline bool u16_mul_overflow(u16_t a, u16_t b, u16_t *result)
{
u16_t c = a * b;

*result = c;

return a != 0 && (c / a) != b;
}

static inline bool u32_mul_overflow(u32_t a, u32_t b, u32_t *result)
{
u32_t c = a * b;
Expand Down
20 changes: 15 additions & 5 deletions subsys/net/lib/coap/coap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ LOG_MODULE_REGISTER(net_coap, CONFIG_COAP_LOG_LEVEL);

#include <zephyr/types.h>
#include <sys/byteorder.h>
#include <sys/math_extras.h>

#include <net/net_ip.h>
#include <net/net_core.h>
Expand Down Expand Up @@ -469,7 +470,9 @@ static int parse_option(u8_t *data, u16_t offset, u16_t *pos,
return -EINVAL;
}

*opt_len += hdr_len;
if (u16_add_overflow(*opt_len, hdr_len, opt_len)) {
return -EINVAL;
}
}

if (len > COAP_OPTION_NO_EXT) {
Expand All @@ -480,11 +483,15 @@ static int parse_option(u8_t *data, u16_t offset, u16_t *pos,
return -EINVAL;
}

*opt_len += hdr_len;
if (u16_add_overflow(*opt_len, hdr_len, opt_len)) {
return -EINVAL;
}
}

*opt_delta += delta;
*opt_len += len;
if (u16_add_overflow(*opt_delta, delta, opt_delta) ||
u16_add_overflow(*opt_len, len, opt_len)) {
return -EINVAL;
}

if (r == 0) {
if (len == 0U) {
Expand Down Expand Up @@ -519,7 +526,10 @@ static int parse_option(u8_t *data, u16_t offset, u16_t *pos,
return -EINVAL;
}
} else {
*pos += len;
if (u16_add_overflow(*pos, len, pos)) {
return -EINVAL;
}

r = max_len - *pos;
}

Expand Down