Fix: increment buffer offset when failing to copy from user-space

Upon failure to copy from user-space due to failing access ok check, the
ring buffer offset is not incremented, which could generate unreadable
traces because we don't account for the padding we write into the ring
buffer.

Note that this typically won't affect a common use-case of copying
strings from user-space, because unless mprotect is invoked within a
narrow race window (between user strlen and user strcpy), the strlen
will fail on access ok when calculating the space to reserve, which will
match what happens on strcpy.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ic4d9487dd8870a526bae3023bb80f5e6301cec50

diff --git a/include/ringbuffer/backend.h b/include/ringbuffer/backend.h
index 327b199b0858cadb049754ff61e88a4816674da5..1ede713c82de37233c54c86b1b4b20c41e1a7824 100644 (file)
--- a/include/ringbuffer/backend.h
+++ b/include/ringbuffer/backend.h
@@ -313,6 +313,7 @@ fill_buffer:
         * the pollution of static inline code.
         */
        _lib_ring_buffer_memset(bufb, offset, 0, len, 0);
+       ctx->priv.buf_offset += len;
 }
 
 /**
@@ -395,6 +396,7 @@ fill_buffer:
        _lib_ring_buffer_memset(bufb, offset, pad, len - 1, 0);
        offset += len - 1;
        _lib_ring_buffer_memset(bufb, offset, '\0', 1, 0);
+       ctx->priv.buf_offset += len;
 }
 
 /*