Fix: truncation of text array and sequences by NULL terminator

[lttng-ust.git] / libringbuffer / backend.h

diff --git a/libringbuffer/backend.h b/libringbuffer/backend.h
index bced86d96885950e4842a7c394508e86960a978c..698994c21881a78a7c7beb160c0daa3a47e689fe 100644 (file)
--- a/libringbuffer/backend.h
+++ b/libringbuffer/backend.h
@@ -182,6 +182,64 @@ void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *confi
        ctx->buf_offset += len;
 }
 
+/**
+ * lib_ring_buffer_pstrcpy - write to a buffer backend P-string
+ * @config : ring buffer instance configuration
+ * @ctx: ring buffer context. (input arguments only)
+ * @src : source pointer to copy from
+ * @len : length of data to copy
+ * @pad : character to use for padding
+ *
+ * This function copies up to @len bytes of data from a source pointer
+ * to a Pascal String into the buffer backend. If a terminating '\0'
+ * character is found in @src before @len characters are copied, pad the
+ * buffer with @pad characters (e.g.  '\0').
+ *
+ * The length of the pascal strings in the ring buffer is explicit: it
+ * is either the array or sequence length.
+ */
+static inline __attribute__((always_inline))
+void lib_ring_buffer_pstrcpy(const struct lttng_ust_lib_ring_buffer_config *config,
+                          struct lttng_ust_lib_ring_buffer_ctx *ctx,
+                          const char *src, size_t len, char pad)
+{
+       struct channel_backend *chanb = &ctx->chan->backend;
+       struct lttng_ust_shm_handle *handle = ctx->handle;
+       size_t count;
+       size_t offset = ctx->buf_offset;
+       struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
+       void *p;
+
+       if (caa_unlikely(!len))
+               return;
+       /*
+        * Underlying layer should never ask for writes across
+        * subbuffers.
+        */
+       CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
+       backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
+       if (caa_unlikely(!backend_pages)) {
+               if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
+                       return;
+       }
+       p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
+       if (caa_unlikely(!p))
+               return;
+
+       count = lib_ring_buffer_do_strcpy(config, p, src, len);
+       offset += count;
+       /* Padding */
+       if (caa_unlikely(count < len)) {
+               size_t pad_len = len - count;
+
+               p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
+               if (caa_unlikely(!p))
+                       return;
+               lib_ring_buffer_do_memset(p, pad, pad_len);
+       }
+       ctx->buf_offset += len;
+}
+
 /*
  * This accessor counts the number of unread records in a buffer.
  * It only provides a consistent value if no reads not writes are performed