buffer: Add and use ssh_buffer_allocate_size()

Add a small helper for ssh_buffer to ensure that the buffer has a
certain amount of space already preallocated. This can be useful in case
it is known how much data is going to be added to a buffer, to avoid
multiple reallocations.

Make use of it in few places in the library.

Signed-off-by: Pino Toscano <ptoscano@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/buffer.h

@@ -51,6 +51,7 @@ int ssh_buffer_add_u64(ssh_buffer buffer, uint64_t data);
 int ssh_buffer_validate_length(struct ssh_buffer_struct *buffer, size_t len);
 
 void *ssh_buffer_allocate(struct ssh_buffer_struct *buffer, uint32_t len);
+int ssh_buffer_allocate_size(struct ssh_buffer_struct *buffer, uint32_t len);
 int ssh_buffer_pack_va(struct ssh_buffer_struct *buffer,
                        const char *format,
                        int argc,

src/agent.c

@@ -514,6 +514,21 @@ ssh_string ssh_agent_sign_data(ssh_session session,
         return NULL;
     }
 
+    /*
+     * make sure it already can contain all the expected content:
+     * - 1 x uint8_t
+     * - 2 x uint32_t
+     * - 1 x ssh_string (uint8_t + data)
+     */
+    rc = ssh_buffer_allocate_size(request,
+                                  sizeof(uint8_t) * 2 +
+                                  sizeof(uint32_t) * 2 +
+                                  ssh_string_len(key_blob));
+    if (rc < 0) {
+        ssh_buffer_free(request);
+        return NULL;
+    }
+
     /* adds len + blob */
     rc = ssh_buffer_add_ssh_string(request, key_blob);
     ssh_string_free(key_blob);

src/buffer.c

@@ -248,6 +248,34 @@ int ssh_buffer_add_data(struct ssh_buffer_struct *buffer, const void *data, uint
   return 0;
 }
 
+/**
+ * @brief Ensure the buffer has at least a certain preallocated size.
+ *
+ * @param[in]  buffer   The buffer to enlarge.
+ *
+ * @param[in]  len      The length to ensure as allocated.
+ *
+ * @return              0 on success, < 0 on error.
+ */
+int ssh_buffer_allocate_size(struct ssh_buffer_struct *buffer,
+                             uint32_t len)
+{
+    buffer_verify(buffer);
+
+    if (buffer->allocated < len) {
+        if (buffer->pos > 0) {
+            buffer_shift(buffer);
+        }
+        if (realloc_buffer(buffer, len) < 0) {
+            return -1;
+        }
+    }
+
+    buffer_verify(buffer);
+
+    return 0;
+}
+
 /**
  * @internal
  *

src/dh.c

@@ -731,11 +731,20 @@ error:
 }
 
 int ssh_hashbufout_add_cookie(ssh_session session) {
+  int rc;
+
   session->out_hashbuf = ssh_buffer_new();
   if (session->out_hashbuf == NULL) {
     return -1;
   }
 
+  rc = ssh_buffer_allocate_size(session->out_hashbuf,
+                                sizeof(uint8_t) + 16);
+  if (rc < 0) {
+    ssh_buffer_reinit(session->out_hashbuf);
+    return -1;
+  }
+
   if (ssh_buffer_add_u8(session->out_hashbuf, 20) < 0) {
     ssh_buffer_reinit(session->out_hashbuf);
     return -1;
@@ -759,11 +768,20 @@ int ssh_hashbufout_add_cookie(ssh_session session) {
 }
 
 int ssh_hashbufin_add_cookie(ssh_session session, unsigned char *cookie) {
+  int rc;
+
   session->in_hashbuf = ssh_buffer_new();
   if (session->in_hashbuf == NULL) {
     return -1;
   }
 
+  rc = ssh_buffer_allocate_size(session->in_hashbuf,
+                                sizeof(uint8_t) + 20 + 16);
+  if (rc < 0) {
+    ssh_buffer_reinit(session->in_hashbuf);
+    return -1;
+  }
+
   if (ssh_buffer_add_u8(session->in_hashbuf, 20) < 0) {
     ssh_buffer_reinit(session->in_hashbuf);
     return -1;

src/pcap.c

@@ -165,6 +165,12 @@ int ssh_pcap_file_write_packet(ssh_pcap_file pcap, ssh_buffer packet, uint32_t o
 	if(header == NULL)
 		return SSH_ERROR;
 	gettimeofday(&now,NULL);
+    err = ssh_buffer_allocate_size(header,
+                                   sizeof(uint32_t) * 4 +
+                                   ssh_buffer_get_len(packet));
+    if (err < 0) {
+        goto error;
+    }
     err = ssh_buffer_add_u32(header,htonl(now.tv_sec));
     if (err < 0) {
         goto error;
@@ -209,6 +215,12 @@ int ssh_pcap_file_open(ssh_pcap_file pcap, const char *filename){
 	header=ssh_buffer_new();
 	if(header==NULL)
 		return SSH_ERROR;
+    err = ssh_buffer_allocate_size(header,
+                                   sizeof(uint32_t) * 5 +
+                                   sizeof(uint16_t) * 2);
+    if (err < 0) {
+        goto error;
+    }
     err = ssh_buffer_add_u32(header,htonl(PCAP_MAGIC));
     if (err < 0) {
         goto error;

src/sftp.c

@@ -318,6 +318,11 @@ sftp_packet sftp_packet_read(sftp_session sftp) {
     return NULL;
   }
 
+  r = ssh_buffer_allocate_size(packet->payload, 4);
+  if (r < 0) {
+    ssh_set_error_oom(sftp->session);
+    goto error;
+  }
   r=0;
   do {
     // read from channel until 4 bytes have been read or an error occurs
@@ -355,6 +360,11 @@ sftp_packet sftp_packet_read(sftp_session sftp) {
   }
   size--;
 
+  r = ssh_buffer_allocate_size(packet->payload, size);
+  if (r < 0) {
+    ssh_set_error_oom(sftp->session);
+    goto error;
+  }
   while (size > 0 && size < UINT_MAX) {
     r=ssh_channel_read(sftp->channel,buffer,
         sizeof(buffer)>size ? size:sizeof(buffer),0);
@@ -849,6 +859,7 @@ sftp_dir sftp_opendir(sftp_session sftp, const char *path){
   ssh_string path_s;
   ssh_buffer payload;
   uint32_t id;
+  int rc;
 
   payload = ssh_buffer_new();
   if (payload == NULL) {
@@ -864,6 +875,14 @@ sftp_dir sftp_opendir(sftp_session sftp, const char *path){
   }
 
   id = sftp_get_new_id(sftp);
+  rc = ssh_buffer_allocate_size(payload,
+                                sizeof(uint32_t) * 2 + ssh_string_len(path_s));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(payload);
+    ssh_string_free(path_s);
+    return NULL;
+  }
   if (ssh_buffer_add_u32(payload, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(payload, path_s) < 0) {
     ssh_set_error_oom(sftp->session);
@@ -1384,6 +1403,7 @@ sftp_attributes sftp_readdir(sftp_session sftp, sftp_dir dir) {
   sftp_attributes attr;
   ssh_buffer payload;
   uint32_t id;
+  int rc;
 
   if (dir->buffer == NULL) {
     payload = ssh_buffer_new();
@@ -1392,6 +1412,14 @@ sftp_attributes sftp_readdir(sftp_session sftp, sftp_dir dir) {
       return NULL;
     }
 
+    rc = ssh_buffer_allocate_size(payload,
+                                  sizeof(uint32_t) * 2 +
+                                  ssh_string_len(dir->handle));
+    if (rc < 0) {
+      ssh_set_error_oom(sftp->session);
+      ssh_buffer_free(payload);
+      return NULL;
+    }
     id = sftp_get_new_id(sftp);
     if (ssh_buffer_add_u32(payload, htonl(id)) < 0 ||
         ssh_buffer_add_ssh_string(payload, dir->handle) < 0) {
@@ -1509,6 +1537,7 @@ static int sftp_handle_close(sftp_session sftp, ssh_string handle) {
   sftp_message msg = NULL;
   ssh_buffer buffer = NULL;
   uint32_t id;
+  int rc;
 
   buffer = ssh_buffer_new();
   if (buffer == NULL) {
@@ -1516,6 +1545,15 @@ static int sftp_handle_close(sftp_session sftp, ssh_string handle) {
     return -1;
   }
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 2 +
+                                ssh_string_len(handle));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    return -1;
+  }
+
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, handle) < 0) {
@@ -1609,6 +1647,7 @@ sftp_file sftp_open(sftp_session sftp, const char *file, int flags,
   sftp_attributes stat_data;
   uint32_t sftp_flags = 0;
   uint32_t id;
+  int rc;
 
   buffer = ssh_buffer_new();
   if (buffer == NULL) {
@@ -1644,6 +1683,15 @@ sftp_file sftp_open(sftp_session sftp, const char *file, int flags,
       sftp_flags |= SSH_FXF_APPEND;
   }
   SSH_LOG(SSH_LOG_PACKET,"Opening file %s with sftp flags %x",file,sftp_flags);
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 4 +
+                                ssh_string_len(filename));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    ssh_string_free(filename);
+    return NULL;
+  }
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, filename) < 0) {
@@ -2215,6 +2263,7 @@ int sftp_mkdir(sftp_session sftp, const char *directory, mode_t mode) {
   ssh_buffer buffer;
   ssh_string path;
   uint32_t id;
+  int rc;
 
   buffer = ssh_buffer_new();
   if (buffer == NULL) {
@@ -2233,6 +2282,16 @@ int sftp_mkdir(sftp_session sftp, const char *directory, mode_t mode) {
   attr.permissions = mode;
   attr.flags = SSH_FILEXFER_ATTR_PERMISSIONS;
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 2 +
+                                ssh_string_len(path));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    ssh_string_free(path);
+    return -1;
+  }
+
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, path) < 0 ||
@@ -2385,6 +2444,7 @@ int sftp_setstat(sftp_session sftp, const char *file, sftp_attributes attr) {
   ssh_string path;
   sftp_message msg = NULL;
   sftp_status_message status = NULL;
+  int rc;
 
   buffer = ssh_buffer_new();
   if (buffer == NULL) {
@@ -2399,6 +2459,16 @@ int sftp_setstat(sftp_session sftp, const char *file, sftp_attributes attr) {
     return -1;
   }
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 2 +
+                                ssh_string_len(path));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    ssh_string_free(path);
+    return -1;
+  }
+
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, path) < 0 ||
@@ -2592,6 +2662,7 @@ char *sftp_readlink(sftp_session sftp, const char *path) {
   char *lnk;
   uint32_t ignored;
   uint32_t id;
+  int rc;
 
   if (sftp == NULL)
     return NULL;
@@ -2616,6 +2687,16 @@ char *sftp_readlink(sftp_session sftp, const char *path) {
     return NULL;
   }
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 2 +
+                                ssh_string_len(path_s));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    ssh_string_free(path_s);
+    return NULL;
+  }
+
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, path_s) < 0) {
@@ -2710,6 +2791,7 @@ sftp_statvfs_t sftp_statvfs(sftp_session sftp, const char *path) {
   ssh_string ext;
   ssh_buffer buffer;
   uint32_t id;
+  int rc;
 
   if (sftp == NULL)
     return NULL;
@@ -2743,6 +2825,18 @@ sftp_statvfs_t sftp_statvfs(sftp_session sftp, const char *path) {
     return NULL;
   }
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 3 +
+                                ssh_string_len(ext) +
+                                ssh_string_len(pathstr));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    ssh_string_free(ext);
+    ssh_string_free(pathstr);
+    return NULL;
+  }
+
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, ext) < 0 ||
@@ -2823,6 +2917,15 @@ int sftp_fsync(sftp_file file)
         goto done;
     }
 
+    rc = ssh_buffer_allocate_size(buffer,
+                                        sizeof(uint32_t) * 3 +
+                                        ssh_string_len(ext) +
+                                        ssh_string_len(file->handle));
+    if (rc < 0) {
+        ssh_set_error_oom(sftp->session);
+        goto done;
+    }
+
     id = sftp_get_new_id(sftp);
     rc = ssh_buffer_add_u32(buffer, htonl(id));
     if (rc < 0) {
@@ -2915,6 +3018,7 @@ sftp_statvfs_t sftp_fstatvfs(sftp_file file) {
   ssh_string ext;
   ssh_buffer buffer;
   uint32_t id;
+  int rc;
 
   if (file == NULL) {
     return NULL;
@@ -2934,6 +3038,17 @@ sftp_statvfs_t sftp_fstatvfs(sftp_file file) {
     return NULL;
   }
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 3 +
+                                ssh_string_len(ext) +
+                                ssh_string_len(file->handle));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    ssh_string_free(ext);
+    return NULL;
+  }
+
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, ext) < 0 ||
@@ -3002,6 +3117,7 @@ char *sftp_canonicalize_path(sftp_session sftp, const char *path) {
   char *cname;
   uint32_t ignored;
   uint32_t id;
+  int rc;
 
   if (sftp == NULL)
     return NULL;
@@ -3023,6 +3139,16 @@ char *sftp_canonicalize_path(sftp_session sftp, const char *path) {
     return NULL;
   }
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 2 +
+                                ssh_string_len(pathstr));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    ssh_string_free(pathstr);
+    return NULL;
+  }
+
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, pathstr) < 0) {
@@ -3087,6 +3213,7 @@ static sftp_attributes sftp_xstat(sftp_session sftp, const char *path,
   ssh_string pathstr;
   ssh_buffer buffer;
   uint32_t id;
+  int rc;
 
   if (path == NULL) {
       ssh_set_error_invalid(sftp->session);
@@ -3106,6 +3233,16 @@ static sftp_attributes sftp_xstat(sftp_session sftp, const char *path,
     return NULL;
   }
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 2 +
+                                ssh_string_len(pathstr));
+  if (rc < 0) {
+    ssh_set_error_oom(sftp->session);
+    ssh_buffer_free(buffer);
+    ssh_string_free(pathstr);
+    return NULL;
+  }
+
   id = sftp_get_new_id(sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, pathstr) < 0) {
@@ -3166,6 +3303,7 @@ sftp_attributes sftp_fstat(sftp_file file) {
   sftp_message msg = NULL;
   ssh_buffer buffer;
   uint32_t id;
+  int rc;
 
   buffer = ssh_buffer_new();
   if (buffer == NULL) {
@@ -3173,6 +3311,15 @@ sftp_attributes sftp_fstat(sftp_file file) {
     return NULL;
   }
 
+  rc = ssh_buffer_allocate_size(buffer,
+                                sizeof(uint32_t) * 2 +
+                                ssh_string_len(file->handle));
+  if (rc < 0) {
+    ssh_set_error_oom(file->sftp->session);
+    ssh_buffer_free(buffer);
+    return NULL;
+  }
+
   id = sftp_get_new_id(file->sftp);
   if (ssh_buffer_add_u32(buffer, htonl(id)) < 0 ||
       ssh_buffer_add_ssh_string(buffer, file->handle) < 0) {