fix: resolve all security issues (#154, #156, #157, #159, #160, #161, #162, #170)

src/server/server.c

@@ -69,7 +69,7 @@ int receive_files(Config* config, int fd) {
         }
         char* full_path = path_cat(config->receive_root_directory, check_path);
         struct stat st;
-        bool has_old = full_path && stat(full_path, &st) == 0;
+        bool has_old = full_path && lstat(full_path, &st) == 0;
         bool match = has_old && (unsigned long long)st.st_size == check_size &&
                      (long long)st.st_mtime == check_mtime;
         if (match)

src/shared/compression.c

@@ -78,14 +78,21 @@ Data* data_decompress(Data* compressed_data) {
     return NULL;
   }
 
+  // ZSTD_CONTENTSIZE_UNKNOWN (~2^64) can cause massive allocation;
+  // fall back to a conservative estimate (3x compressed size) when unknown.
+  if (dst_size == ZSTD_CONTENTSIZE_UNKNOWN) {
+    dst_size = compressed_data->size * 3;
+    if (dst_size < INITIAL_DECOMPRESS_BUF_SIZE)
+      dst_size = INITIAL_DECOMPRESS_BUF_SIZE;
+  }
+
   ZSTD_DCtx* dctx = ZSTD_createDCtx();
   if (!dctx) {
     log_message(LOG_LEVEL_ERROR, "Failed to create ZSTD decompression context");
     return NULL;
   }
 
-  size_t buf_size =
-      (!ZSTD_isError(dst_size) && dst_size > 0) ? (size_t)dst_size : INITIAL_DECOMPRESS_BUF_SIZE;
+  size_t buf_size = (dst_size > 0) ? (size_t)dst_size : INITIAL_DECOMPRESS_BUF_SIZE;
   Data* uncompressed_data = data_create_empty(buf_size);
   if (!uncompressed_data) {
     log_message(LOG_LEVEL_ERROR, "Failed to allocate decompression buffer");

src/shared/delta.c

@@ -1,5 +1,6 @@
 #include "delta.h"
 #include "log.h"
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -7,6 +8,10 @@
 #define XXH_IMPLEMENTATION
 #include <xxhash.h>
 
+/* Maximum number of blocks/instructions allowed from the wire to prevent OOM */
+#define MAX_DELTA_BLOCKS       (1024U * 1024U)   /* 1M signature blocks */
+#define MAX_DELTA_INSTRUCTIONS (1024U * 1024U)   /* 1M delta instructions */
+
 uint32_t delta_adler32(const void* data, uint32_t len) {
   const uint8_t* p = (const uint8_t*)data;
   uint32_t s1 = 1;
@@ -101,6 +106,14 @@ DeltaSignature* delta_signature_deserialize(const Data* data) {
   memcpy(&sig->block_count, buf + pos, sizeof(uint32_t));
   pos += sizeof(uint32_t);
 
+  // Reject unreasonably large block counts to prevent OOM
+  if (sig->block_count > MAX_DELTA_BLOCKS) {
+    log_message(LOG_LEVEL_ERROR, "Delta signature block count %u exceeds maximum %u",
+                sig->block_count, MAX_DELTA_BLOCKS);
+    free(sig);
+    return NULL;
+  }
+
   uint64_t expected = sizeof(uint64_t) + sizeof(uint32_t) + sizeof(uint32_t) +
                       (uint64_t)sig->block_count * (sizeof(uint32_t) + sizeof(uint32_t));
   if (data->size < expected) {
@@ -340,6 +353,14 @@ Delta* delta_deserialize(const Data* data) {
   memcpy(&delta->instruction_count, buf + pos, sizeof(uint32_t));
   pos += sizeof(uint32_t);
 
+  // Reject unreasonably large instruction counts to prevent OOM
+  if (delta->instruction_count > MAX_DELTA_INSTRUCTIONS) {
+    log_message(LOG_LEVEL_ERROR, "Delta instruction count %u exceeds maximum %u",
+                delta->instruction_count, MAX_DELTA_INSTRUCTIONS);
+    free(delta);
+    return NULL;
+  }
+
   delta->instructions = malloc(delta->instruction_count * sizeof(DeltaInstruction));
   if (!delta->instructions) {
     free(delta);

src/shared/file.c

@@ -134,9 +134,64 @@ bool file_save_to_disk(const char* root_directory, File* file, const Config* con
     log_message(LOG_LEVEL_ERROR, "Path traversal detected in file path: %s", file->path);
     return false;
   }
-  char* disk_path = path_cat((char*)root_directory, file->path);
-  if (disk_path == NULL)
+
+  // Resolve the destination root to its real path, preventing symlink-based escapes.
+  // If the root does not yet exist, try to create it so realpath can succeed.
+  char* resolved_root = realpath(root_directory, NULL);
+  if (resolved_root == NULL) {
+    if (mkdir_r(root_directory)) {
+      resolved_root = realpath(root_directory, NULL);
+    }
+  }
+  if (resolved_root == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Failed to resolve destination root: %s", root_directory);
     return false;
+  }
+
+  char* disk_path = path_cat(resolved_root, file->path);
+  if (disk_path == NULL) {
+    free(resolved_root);
+    return false;
+  }
+
+  // Ensure the target directory exists so the parent can be resolved for path safety.
+  char* dir_dup = str_dup(disk_path);
+  if (!dir_dup) {
+    free(resolved_root);
+    free(disk_path);
+    return false;
+  }
+  char* dir_str = dirname(dir_dup);
+  // Create the directory if needed (no-op if it already exists) so realpath can resolve it.
+  if (!mkdir_r(dir_str)) {
+    free(dir_dup);
+    free(resolved_root);
+    free(disk_path);
+    return false;
+  }
+  char* resolved_dir = realpath(dir_str, NULL);
+  free(dir_dup);
+  if (resolved_dir == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Failed to resolve directory for: %s", disk_path);
+    free(resolved_root);
+    free(disk_path);
+    return false;
+  }
+
+  // Verify that the resolved directory is inside the resolved root.
+  // Both are canonical absolute paths — this prevents symlink-based escapes.
+  size_t root_len = strlen(resolved_root);
+  if (strncmp(resolved_dir, resolved_root, root_len) != 0 ||
+      (resolved_dir[root_len] != '\0' && resolved_dir[root_len] != '/')) {
+    log_message(LOG_LEVEL_ERROR, "Path escape detected: %s is outside %s", disk_path, root_directory);
+    free(resolved_dir);
+    free(resolved_root);
+    free(disk_path);
+    return false;
+  }
+  free(resolved_dir);
+  free(resolved_root);
+
   bool ok = to_disk(disk_path, file->data->data, file->data->size);
   if (ok)
     file_restore_metadata(disk_path, file->metadata);
@@ -341,7 +396,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
 
   char* full_path = path_cat(config->receive_root_directory, check_path);
   struct stat st;
-  bool has_old_file = (full_path && stat(full_path, &st) == 0);
+  bool has_old_file = (full_path && lstat(full_path, &st) == 0);
   unsigned long long old_size = has_old_file ? (unsigned long long)st.st_size : 0;
 
   bool match = has_old_file && (unsigned long long)st.st_size == check_size &&

src/shared/protocol.c

@@ -9,7 +9,7 @@
 #include <time.h>
 #include <unistd.h>
 
-#define MAX_DATA_SIZE (256ULL * 1024 * 1024)          /* 256 MB max per message */
+#define MAX_DATA_SIZE (100ULL * 1024 * 1024)          /* 100 MB max per data message */
 #define RECEIVE_TIMEOUT_SEC 60                        /* 60 second per-message timeout */
 #define MAX_CONNECTION_MEMORY (1024ULL * 1024 * 1024) /* 1 GB total per connection */
 
@@ -186,9 +186,9 @@ char* receive_str(int file_descriptor) {
   size_t size;
   if (!receive_n_data(file_descriptor, &size, sizeof(size_t)))
     return NULL;
-  if (size > MAX_DATA_SIZE) {
+  if (size > MAX_STRING_SIZE) {
     log_message(LOG_LEVEL_ERROR, "String size %zu exceeds maximum %llu", size,
-                (unsigned long long)MAX_DATA_SIZE);
+                (unsigned long long)MAX_STRING_SIZE);
     return NULL;
   }
   char* data = (char*)malloc(size + 1);

src/shared/protocol.h

@@ -5,8 +5,11 @@
 #include <stdbool.h>
 #include <stddef.h>
 
-/* Maximum allowed string size for receive_str (10 MB) */
-#define MAX_STRING_SIZE (10 * 1024 * 1024)
+/* Maximum allowed string size for receive_str (64 KB) */
+#define MAX_STRING_SIZE (64 * 1024)
+
+/* Maximum allowed data payload size for receive_data (100 MB) */
+#define MAX_DATA_PAYLOAD_SIZE (100ULL * 1024 * 1024)
 
 typedef struct ssl_st SSL;
 

src/shared/transport_tls.c

@@ -79,25 +79,38 @@ static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key
   return ctx;
 }
 
-static SSL* wrap_fd_with_ssl(int fd, SSL_CTX* ctx, bool is_server) {
+static SSL* wrap_fd_with_ssl(int fd, SSL_CTX* ctx, bool is_server, const char* hostname) {
   SSL* ssl = SSL_new(ctx);
   if (!ssl) {
     log_message(LOG_LEVEL_ERROR, "Failed to create SSL object");
     return NULL;
   }
   SSL_set_fd(ssl, fd);
-  int ret;
-  if (is_server)
-    ret = SSL_accept(ssl);
-  else
-    ret = SSL_connect(ssl);
 
-  if (ret <= 0) {
-    log_message(LOG_LEVEL_ERROR, "SSL %s failed", is_server ? "accept" : "connect");
-    log_ssl_errors();
-    SSL_free(ssl);
-    return NULL;
+  // Enable hostname verification for client connections when a hostname is provided.
+  // Must be done before SSL_connect to take effect during the handshake.
+  if (!is_server && hostname) {
+    SSL_set1_host(ssl, hostname);
   }
+
+  // Retry SSL_accept/SSL_connect on WANT_READ/WANT_WRITE (non-blocking handshake)
+  int ret;
+  do {
+    if (is_server)
+      ret = SSL_accept(ssl);
+    else
+      ret = SSL_connect(ssl);
+
+    if (ret <= 0) {
+      int ssl_err = SSL_get_error(ssl, ret);
+      if (ssl_err == SSL_ERROR_WANT_READ || ssl_err == SSL_ERROR_WANT_WRITE)
+        continue;
+      log_message(LOG_LEVEL_ERROR, "SSL %s failed", is_server ? "accept" : "connect");
+      log_ssl_errors();
+      SSL_free(ssl);
+      return NULL;
+    }
+  } while (ret <= 0);
   return ssl;
 }
 
@@ -117,7 +130,7 @@ struct tls_child_ctx {
 
 static void tls_child_fn(int fd, void* arg) {
   struct tls_child_ctx* ctx = (struct tls_child_ctx*)arg;
-  SSL* ssl = wrap_fd_with_ssl(fd, ctx->ssl_ctx, true);
+  SSL* ssl = wrap_fd_with_ssl(fd, ctx->ssl_ctx, true, NULL);
   if (!ssl)
     return;
   io_set_ssl(ssl);
@@ -151,12 +164,16 @@ bool client_connect_tls(Client* client, char* host, int port, const char* cert_p
     return false;
   client->ssl_ctx = ctx;
 
-  SSL* ssl = wrap_fd_with_ssl(client->file_descriptor, ctx, false);
+  // Pass the server hostname for TLS hostname verification (SSL_set1_host
+  // is called inside wrap_fd_with_ssl before the handshake when ca_path is set).
+  const char* verify_host = ca_path ? host : NULL;
+  SSL* ssl = wrap_fd_with_ssl(client->file_descriptor, ctx, false, verify_host);
   if (!ssl) {
     SSL_CTX_free(ctx);
     client->ssl_ctx = NULL;
     return false;
   }
+
   client->ssl = ssl;
   io_set_ssl(ssl);
   return true;

src/shared/utils.c

@@ -126,7 +126,13 @@ static void delete_extras_walk(const char* abs_path, const char* rel_path, Array
     char* child_abs = path_cat((char*)abs_path, entry->d_name);
     char* child_rel = path_cat((char*)rel_path, entry->d_name);
     struct stat st;
-    if (stat(child_abs, &st) != 0) {
+    if (lstat(child_abs, &st) != 0) {
+      free(child_abs);
+      free(child_rel);
+      continue;
+    }
+    // Skip symlinks to prevent following them outside the destination tree
+    if (S_ISLNK(st.st_mode)) {
       free(child_abs);
       free(child_rel);
       continue;

tests/integration/test_tls.py

@@ -37,15 +37,23 @@ def _generate_certs(cert_dir):
     ], check=True, capture_output=True)
 
     # Server key + CSR + cert (signed by CA)
+    # Use a config file to include IP SAN 127.0.0.1 so hostname verification passes
+    san_config = os.path.join(cert_dir, "server_san.conf")
+    with open(san_config, "w") as f:
+        f.write("[req]\ndistinguished_name = req_distinguished_name\nreq_extensions = v3_req\n\n")
+        f.write("[req_distinguished_name]\nCN = localhost\n\n")
+        f.write("[v3_req]\nsubjectAltName = @alt_names\n\n")
+        f.write("[alt_names]\nDNS.1 = localhost\nIP.1 = 127.0.0.1\n")
     subprocess.run([
         "openssl", "req", "-newkey", "rsa:2048", "-nodes",
         "-keyout", server_key, "-out", os.path.join(cert_dir, "server.csr"),
-        "-subj", "/CN=localhost",
+        "-subj", "/CN=localhost", "-config", san_config,
     ], check=True, capture_output=True)
     subprocess.run([
         "openssl", "x509", "-req", "-in", os.path.join(cert_dir, "server.csr"),
         "-CA", ca_cert, "-CAkey", ca_key, "-CAcreateserial",
         "-out", server_cert, "-days", "1",
+        "-extfile", san_config, "-extensions", "v3_req",
     ], check=True, capture_output=True)
 
     # Client key + CSR + cert (signed by CA)