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Verify that the requested allocation size does not overflow. #109

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Jul 25, 2018
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Verify that the requested allocation size does not overflow. #109

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fe1255e
Verify that the requested allocation size does not overflow.
malsbat Jul 23, 2018
488e398
Add comment to clarify overflow calculation.
malsbat Jul 24, 2018
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10 changes: 9 additions & 1 deletion src/logging.c
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Original file line number Diff line number Diff line change
Expand Up @@ -417,9 +417,17 @@ void rcutils_log(
) \
size_t old_output_buffer_len = strlen(output_buffer); \
size_t required_output_buffer_size = old_output_buffer_len + n + 1; \
if (required_output_buffer_size <= old_output_buffer_len) { \
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Is this the overflow case? If so a comment would be good to indicate this.

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Yes, this is the overflow case. I can add a comment.

fprintf(stderr, "required buffer for logging output too large\n"); \
goto cleanup; \
} \
if (required_output_buffer_size > output_buffer_size) { \
do { \
output_buffer_size *= 2; \
if (output_buffer_size <= (SIZE_MAX / 2)) { \
output_buffer_size *= 2; \
} else { \
output_buffer_size = SIZE_MAX; \
} \
} while (required_output_buffer_size > output_buffer_size); \
if (output_buffer == static_output_buffer) { \
void * dynamic_output_buffer = g_rcutils_logging_allocator.allocate( \
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7 changes: 7 additions & 0 deletions src/string_map.c
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Expand Up @@ -21,6 +21,7 @@ extern "C"

#include <assert.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>

#include "./common.h"
Expand Down Expand Up @@ -166,6 +167,12 @@ rcutils_string_map_reserve(rcutils_string_map_t * string_map, size_t capacity)
// note that realloc when the pointer is NULL is the same as malloc
// note also that realloc will shrink the space if needed

// ensure that reallocate won't overflow capacity
if (capacity > (SIZE_MAX / sizeof(char *))) {
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Can you explain in what cases this might occur?

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I did not trace down all the callers of rcutils_string_map_reserve so it may not occur in practice today. However, it may occur if the requested capacity is greater than SIZE_MAX / 4 or SIZE_MAX / 8, depending on the pointer size.

I'll also note that glibc provides an explicit reallocarray() function that is the same as realloc() but includes the overflow check as done here.

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We can consider adding a wrapper function in rcutils/allocator.h to preform this check if you like, I already created a reallocf function along these lines:

  • rcutils/include/rcutils/allocator.h

    Lines 129 to 137 in 244fa98

    /// Emulate the behavior of [reallocf](https://linux.die.net/man/3/reallocf).
    /**
    * This function will return `NULL` if the allocator is `NULL` or has `NULL` for
    * function pointer fields.
    */
    RCUTILS_PUBLIC
    RCUTILS_WARN_UNUSED
    void *
    rcutils_reallocf(void * pointer, size_t size, rcutils_allocator_t * allocator);

  • rcutils/src/allocator.c

    Lines 100 to 117 in 244fa98

    void *
    rcutils_reallocf(void * pointer, size_t size, rcutils_allocator_t * allocator)
    {
    if (!rcutils_allocator_is_valid(allocator)) {
    // cannot deallocate pointer, so print message to stderr and return NULL
    #if RCUTILS_REPORT_ERROR_HANDLING_ERRORS
    RCUTILS_SAFE_FWRITE_TO_STDERR(
    "[rcutils|allocator.c:" RCUTILS_STRINGIFY(__LINE__) "] rcutils_reallocf(): "
    "invalid allocator or allocator function pointers, memory leaked\n");
    #endif
    return NULL;
    }
    void * new_pointer = allocator->reallocate(pointer, size, allocator->state);
    if (NULL == new_pointer) {
    allocator->deallocate(pointer, allocator->state);
    }
    return new_pointer;
    }

Otherwise, this check here seems fine.

RCUTILS_SET_ERROR_MSG("requested capacity for string_map too large", allocator)
return RCUTILS_RET_BAD_ALLOC;
}

// resize the keys, assigning the result only if it succeeds
char ** new_keys =
allocator.reallocate(string_map->impl->keys, capacity * sizeof(char *), allocator.state);
Expand Down