From 45d8b80c2ac5d21cd1e2954431fb676bc2b1e099 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Fri, 22 Dec 2017 20:32:35 -0500 Subject: ring-buffer: Mask out the info bits when returning buffer page length Two info bits were added to the "commit" part of the ring buffer data page when returned to be consumed. This was to inform the user space readers that events have been missed, and that the count may be stored at the end of the page. What wasn't handled, was the splice code that actually called a function to return the length of the data in order to zero out the rest of the page before sending it up to user space. These data bits were returned with the length making the value negative, and that negative value was not checked. It was compared to PAGE_SIZE, and only used if the size was less than PAGE_SIZE. Luckily PAGE_SIZE is unsigned long which made the compare an unsigned compare, meaning the negative size value did not end up causing a large portion of memory to be randomly zeroed out. Cc: stable@vger.kernel.org Fixes: 66a8cb95ed040 ("ring-buffer: Add place holder recording of dropped events") Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/ring_buffer.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'kernel/trace/ring_buffer.c') diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index c87766c1c204..e06cde093f76 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -280,6 +280,8 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data); /* Missed count stored at end */ #define RB_MISSED_STORED (1 << 30) +#define RB_MISSED_FLAGS (RB_MISSED_EVENTS|RB_MISSED_STORED) + struct buffer_data_page { u64 time_stamp; /* page time stamp */ local_t commit; /* write committed index */ @@ -331,7 +333,9 @@ static void rb_init_page(struct buffer_data_page *bpage) */ size_t ring_buffer_page_len(void *page) { - return local_read(&((struct buffer_data_page *)page)->commit) + struct buffer_data_page *bpage = page; + + return (local_read(&bpage->commit) & ~RB_MISSED_FLAGS) + BUF_PAGE_HDR_SIZE; } -- cgit From ae415fa4c5248a8cf4faabd5a3c20576cb1ad607 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Fri, 22 Dec 2017 21:19:29 -0500 Subject: ring-buffer: Do no reuse reader page if still in use To free the reader page that is allocated with ring_buffer_alloc_read_page(), ring_buffer_free_read_page() must be called. For faster performance, this page can be reused by the ring buffer to avoid having to free and allocate new pages. The issue arises when the page is used with a splice pipe into the networking code. The networking code may up the page counter for the page, and keep it active while sending it is queued to go to the network. The incrementing of the page ref does not prevent it from being reused in the ring buffer, and this can cause the page that is being sent out to the network to be modified before it is sent by reading new data. Add a check to the page ref counter, and only reuse the page if it is not being used anywhere else. Cc: stable@vger.kernel.org Fixes: 73a757e63114d ("ring-buffer: Return reader page back into existing ring buffer") Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/ring_buffer.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'kernel/trace/ring_buffer.c') diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index e06cde093f76..9ab18995ff1e 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4404,8 +4404,13 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, int cpu, void *data) { struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu]; struct buffer_data_page *bpage = data; + struct page *page = virt_to_page(bpage); unsigned long flags; + /* If the page is still in use someplace else, we can't reuse it */ + if (page_ref_count(page) > 1) + goto out; + local_irq_save(flags); arch_spin_lock(&cpu_buffer->lock); @@ -4417,6 +4422,7 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, int cpu, void *data) arch_spin_unlock(&cpu_buffer->lock); local_irq_restore(flags); + out: free_page((unsigned long)bpage); } EXPORT_SYMBOL_GPL(ring_buffer_free_read_page); -- cgit