From 0bf3c920174f81b8675984010785b8af9b9b1b59 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Sun, 30 Jun 2013 17:45:32 -0400 Subject: [PATCH] Fix: handle writes of length 0 lib_ring_buffer_write() could be passed a length of 0. This typically has no side-effect as far as writing into the buffers is concerned, except for one detail: in overwrite mode, there is a check to make sure the sub-buffer can be written into. This check is performed even if length is 0. In the case where this would fall exactly at the end of a sub-buffer, the check would fail, because the offset would fall exactly at the beginning of the next sub-buffer. Signed-off-by: Mathieu Desnoyers --- libringbuffer/backend.h | 2 ++ libringbuffer/ring_buffer_backend.c | 5 ++++- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/libringbuffer/backend.h b/libringbuffer/backend.h index 125d0a50..feefc7a3 100644 --- a/libringbuffer/backend.h +++ b/libringbuffer/backend.h @@ -84,6 +84,8 @@ void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages; unsigned long sb_bindex, id; + if (caa_unlikely(!len)) + return; offset &= chanb->buf_size - 1; sbidx = offset >> chanb->subbuf_size_order; id = shmp_index(handle, bufb->buf_wsb, sbidx)->id; diff --git a/libringbuffer/ring_buffer_backend.c b/libringbuffer/ring_buffer_backend.c index e7a00144..3db1f860 100644 --- a/libringbuffer/ring_buffer_backend.c +++ b/libringbuffer/ring_buffer_backend.c @@ -381,8 +381,9 @@ size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend *bufb, size * @dest : destination address * @len : destination's length * - * return string's length + * Return string's length, or -EINVAL on error. * Should be protected by get_subbuf/put_subbuf. + * Destination length should be at least 1 to hold '\0'. */ int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb, size_t offset, void *dest, size_t len, struct lttng_ust_shm_handle *handle) @@ -394,6 +395,8 @@ int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb, si struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages; unsigned long sb_bindex, id; + if (caa_unlikely(!len)) + return -EINVAL; offset &= chanb->buf_size - 1; orig_offset = offset; id = bufb->buf_rsb.id; -- 2.34.1