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tracing: Check length before giving out the filter buffer

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commit b220c049d5196dd94d992dd2dc8cba1a5e6123bf upstream.

When filters are used by trace events, a page is allocated on each CPU and
used to copy the trace event fields to this page before writing to the ring
buffer. The reason to use the filter and not write directly into the ring
buffer is because a filter may discard the event and there's more overhead
on discarding from the ring buffer than the extra copy.

The problem here is that there is no check against the size being allocated
when using this page. If an event asks for more than a page size while being
filtered, it will get only a page, leading to the caller writing more that
what was allocated.

Check the length of the request, and if it is more than PAGE_SIZE minus the
header default back to allocating from the ring buffer directly. The ring
buffer may reject the event if its too big anyway, but it wont overflow.

Link: https://lore.kernel.org/ath10k/1612839593-2308-1-git-send-email-wgong@codeaurora.org/

Cc: stable@vger.kernel.org
Fixes: 0fc1b09ff1 ("tracing: Use temp buffer when filtering events")
Reported-by: Wen Gong <wgong@codeaurora.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Steven Rostedt (VMware) 2021-02-10 11:53:22 -05:00 committed by Greg Kroah-Hartman
parent a38c1ee166
commit 7c93d8cff5
1 changed files with 1 additions and 1 deletions
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2
kernel/trace/trace.c
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@ -2745,7 +2745,7 @@ trace_event_buffer_lock_reserve(struct trace_buffer **current_rb,
(entry = this_cpu_read(trace_buffered_event))) { (entry = this_cpu_read(trace_buffered_event))) {
/* Try to use the per cpu buffer first */ /* Try to use the per cpu buffer first */
val = this_cpu_inc_return(trace_buffered_event_cnt); val = this_cpu_inc_return(trace_buffered_event_cnt);
if (val == 1) { if ((len < (PAGE_SIZE - sizeof(*entry))) && val == 1) {
trace_event_setup(entry, type, flags, pc); trace_event_setup(entry, type, flags, pc);
entry->array[0] = len; entry->array[0] = len;
return entry; return entry;