perf session: Remap buf if there is no space for event

[ Upstream commit bc21e74d4775f883ae1f542c1f1dc7205b15d925 ]

If a perf event doesn't fit into remaining buffer space return NULL to
remap buf and fetch the event again.

Keep the logic to error out on inadequate input from fuzzing.

This fixes perf failing on ChromeOS (with 32b userspace):

  $ perf report -v -i perf.data
  ...
  prefetch_event: head=0x1fffff8 event->header_size=0x30, mmap_size=0x2000000: fuzzed or compressed perf.data?
  Error:
  failed to process sample

Fixes: 57fc032ad643ffd0 ("perf session: Avoid infinite loop when seeing invalid header.size")
Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Denis Nikitin <denik@chromium.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220330031130.2152327-1-denik@chromium.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 352f16076e01f70ef91ebebdd7809d8cf4c0c05f..562e9b8080272a213814b1c64ca9fa515bb43069 100644 (file)
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -2076,6 +2076,7 @@ prefetch_event(char *buf, u64 head, size_t mmap_size,
               bool needs_swap, union perf_event *error)
 {
        union perf_event *event;
+       u16 event_size;
 
        /*
         * Ensure we have enough space remaining to read
@@ -2088,15 +2089,23 @@ prefetch_event(char *buf, u64 head, size_t mmap_size,
        if (needs_swap)
                perf_event_header__bswap(&event->header);
 
-       if (head + event->header.size <= mmap_size)
+       event_size = event->header.size;
+       if (head + event_size <= mmap_size)
                return event;
 
        /* We're not fetching the event so swap back again */
        if (needs_swap)
                perf_event_header__bswap(&event->header);
 
-       pr_debug("%s: head=%#" PRIx64 " event->header_size=%#x, mmap_size=%#zx:"
-                " fuzzed or compressed perf.data?\n",__func__, head, event->header.size, mmap_size);
+       /* Check if the event fits into the next mmapped buf. */
+       if (event_size <= mmap_size - head % page_size) {
+               /* Remap buf and fetch again. */
+               return NULL;
+       }
+
+       /* Invalid input. Event size should never exceed mmap_size. */
+       pr_debug("%s: head=%#" PRIx64 " event->header.size=%#x, mmap_size=%#zx:"
+                " fuzzed or compressed perf.data?\n", __func__, head, event_size, mmap_size);
 
        return error;
 }