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 d8857d1b6d7c19e926f252a4b47a07ee4eb75dd2..c64953dabcf5484d16e7415aadd9c7a40957d7d4 100644 (file)
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -2082,6 +2082,7 @@ 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
@@ -2094,15 +2095,23 @@ 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;
 }