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fix(file): reject reads that do not fit the result buffer #114

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fix(file): reject reads that do not fit the result buffer #114

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9 changes: 8 additions & 1 deletion src/tools/file.c
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Original file line number Diff line number Diff line change
Expand Up @@ -259,7 +259,14 @@ static int file_read(const char *path, char *result_buf, size_t max_len)
return -1;
}
size_t to_read = (size_t)sz;
if (to_read >= max_len - 1) to_read = max_len - 1;
/* A prefix with return 0 is the whole file to the model. write_file would
* then replace the original and drop the unread tail. */
if (to_read + 1 > max_len) {
fclose(f);
snprintf(result_buf, max_len,
"{\"error\":\"file exceeds result buffer\",\"bytes\":%ld}", sz);
return -1;
}
size_t n = fread(result_buf, 1, to_read, f);
fclose(f);
result_buf[n] = '\0';
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43 changes: 43 additions & 0 deletions tests/test_file.c
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Expand Up @@ -563,6 +563,48 @@ static void test_write_in_workspace_symlink_alias_rejected(void)
rmdir(tmpdir);
}

static void test_read_rejects_file_larger_than_result_buffer(void)
{
char tmpdir[64];
char notes_path[PATH_MAX];
char config_path[PATH_MAX];
char args[PATH_MAX + 64];
char buf[32];
char exact[8];
FILE *f;
config_t *cfg;
const tool_t *t;
int i;

snprintf(tmpdir, sizeof(tmpdir), "/tmp/sc_test_readcap_%d", (int)getpid());
if (mkdir(tmpdir, 0755) != 0 && errno != EEXIST)
return;
snprintf(notes_path, sizeof(notes_path), "%s/notes.md", tmpdir);
f = fopen(notes_path, "w");
MU_ASSERT(f != NULL, "create oversized notes.md");
for (i = 0; i < 64; i++)
fputc('A', f);
fclose(f);
cfg = make_ws_config(tmpdir, config_path, sizeof(config_path));
MU_ASSERT(cfg != NULL, "readcap: load config");
tool_file_set_config(cfg);
t = tool_file_get();
snprintf(args, sizeof(args), "{\"operation\":\"read_file\",\"path\":\"%s\"}", notes_path);
MU_ASSERT(t->execute(args, buf, sizeof(buf)) == -1, "oversize read fails");
MU_ASSERT(strstr(buf, "error") != NULL, "oversize read reports an error");
MU_ASSERT(strstr(buf, "AAAAAAAAAAAAAAAA") == NULL, "oversize read is not a raw prefix");
f = fopen(notes_path, "w");
MU_ASSERT(f != NULL, "rewrite exact-fit notes.md");
fputs("0123456", f);
fclose(f);
MU_ASSERT(t->execute(args, exact, sizeof(exact)) == 0, "exact-fit read succeeds");
MU_ASSERT(strcmp(exact, "0123456") == 0, "exact-fit read returns the whole file");
config_free(cfg);
unlink(config_path);
unlink(notes_path);
rmdir(tmpdir);
}

int main(void)
{
MU_RUN(test_file_read_write_list);
Expand All @@ -577,6 +619,7 @@ int main(void)
MU_RUN(test_file_write_failure_preserves_existing);
MU_RUN(test_write_does_not_clobber_sibling_tmp);
MU_RUN(test_write_in_workspace_symlink_alias_rejected);
MU_RUN(test_read_rejects_file_larger_than_result_buffer);
printf("%d tests run, %d failed\n", tests_run, tests_failed);
return tests_failed ? 1 : 0;
}
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