perf header: Byte-swap build ID event pid and bounds check section entries

perf_header__read_build_ids() swaps the event header fields for cross-endian
perf.data files but not bev.pid. This causes perf_session__findnew_machine()
to look up the wrong machine for guest VM build IDs, misattributing them.
Swap bev.pid alongside the header fields.

Also add a build_id_swap callback for stream-mode build ID events,
and validate NUL-termination of build_id.filename on the native-endian
delivery path (perf_session__process_user_event) — events with
unterminated filenames are skipped.

Harden perf_header__read_build_ids() against crafted perf.data files:

- Add overflow check on offset + size to prevent wrap past ULLONG_MAX.
- Reject bev.header.size == 0 which would loop forever.
- Reject bev.header.size > remaining section to prevent reading past
  the section boundary.
- Guard memcmp(filename, "nel.kallsyms]", 13) with len >= 13 to avoid
  reading uninitialized stack memory on short filenames.
- Force NUL-termination of filename before passing it to functions
  like machine__findnew_dso() that use strlen/strcmp.

Reported-by: sashiko-bot@kernel.org # Running on a local machine
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Assisted-by: Claude:claude-opus-4.6-1m
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <errno.h>
 #include <inttypes.h>
+#include <limits.h>
 #include "string2.h"
 #include <sys/param.h>
 #include <sys/types.h>
@@ -2578,7 +2579,13 @@ static int perf_header__read_build_ids_abi_quirk(struct perf_header *header,
 	} old_bev;
 	struct perf_record_header_build_id bev;
 	char filename[PATH_MAX];
-	u64 limit = offset + size;
+	u64 limit;
+
+	/* Prevent offset + size from wrapping past ULLONG_MAX */
+	if (size > ULLONG_MAX - offset)
+		return -1;
+
+	limit = offset + size;
 
 	while (offset < limit) {
 		ssize_t len;
@@ -2589,6 +2596,10 @@ static int perf_header__read_build_ids_abi_quirk(struct perf_header *header,
 		if (header->needs_swap)
 			perf_event_header__bswap(&old_bev.header);
 
+		/* size == 0 loops forever; size > remaining reads past section */
+		if (old_bev.header.size == 0 || old_bev.header.size > limit - offset)
+			return -1;
+
 		len = old_bev.header.size - sizeof(old_bev);
 		if (len < 0 || len >= PATH_MAX) {
 			pr_warning("invalid build_id filename length %zd\n", len);
@@ -2597,6 +2608,13 @@ static int perf_header__read_build_ids_abi_quirk(struct perf_header *header,
 
 		if (readn(input, filename, len) != len)
 			return -1;
+		/*
+		 * The file data may lack a null terminator, which could
+		 * indicate a corrupt or crafted perf.data file.  Ensure
+		 * filename is always a valid C string before passing it
+		 * to functions like machine__findnew_dso().
+		 */
+		filename[len] = '\0';
 
 		bev.header = old_bev.header;
 
@@ -2624,17 +2642,32 @@ static int perf_header__read_build_ids(struct perf_header *header,
 	struct perf_session *session = container_of(header, struct perf_session, header);
 	struct perf_record_header_build_id bev;
 	char filename[PATH_MAX];
-	u64 limit = offset + size, orig_offset = offset;
+	u64 limit, orig_offset = offset;
 	int err = -1;
 
+	/* Prevent offset + size from wrapping past ULLONG_MAX */
+	if (size > ULLONG_MAX - offset)
+		return -1;
+
+	limit = offset + size;
+
 	while (offset < limit) {
 		ssize_t len;
 
 		if (readn(input, &bev, sizeof(bev)) != sizeof(bev))
 			goto out;
 
-		if (header->needs_swap)
+		if (header->needs_swap) {
 			perf_event_header__bswap(&bev.header);
+			bev.pid = bswap_32(bev.pid);
+		}
+
+		/*
+		 * size == 0 would loop forever (offset never advances);
+		 * size > remaining would read past the section boundary.
+		 */
+		if (bev.header.size == 0 || bev.header.size > limit - offset)
+			goto out;
 
 		len = bev.header.size - sizeof(bev);
 		if (len < 0 || len >= PATH_MAX) {
@@ -2644,6 +2677,13 @@ static int perf_header__read_build_ids(struct perf_header *header,
 
 		if (readn(input, filename, len) != len)
 			goto out;
+		/*
+		 * The file data may lack a null terminator, which could
+		 * indicate a corrupt or crafted perf.data file.  Ensure
+		 * filename is always a valid C string before passing it
+		 * to functions like machine__findnew_dso().
+		 */
+		filename[len] = '\0';
 		/*
 		 * The a1645ce1 changeset:
 		 *
@@ -2657,7 +2697,9 @@ static int perf_header__read_build_ids(struct perf_header *header,
 		 * '[kernel.kallsyms]' string for the kernel build-id has the
 		 * first 4 characters chopped off (where the pid_t sits).
 		 */
-		if (memcmp(filename, "nel.kallsyms]", 13) == 0) {
+		/* Guard short filenames against memcmp reading past the buffer */
+		if (len >= (ssize_t)sizeof("nel.kallsyms]") - 1 &&
+		    memcmp(filename, "nel.kallsyms]", sizeof("nel.kallsyms]") - 1) == 0) {
 			if (lseek(input, orig_offset, SEEK_SET) == (off_t)-1)
 				return -1;
 			return perf_header__read_build_ids_abi_quirk(header, input, offset, size);

tools/perf/util/session.c

@@ -686,6 +686,25 @@ static int perf_event__hdr_attr_swap(union perf_event *event,
 	return 0;
 }
 
+static int perf_event__build_id_swap(union perf_event *event,
+				     bool sample_id_all)
+{
+	event->build_id.pid = bswap_32(event->build_id.pid);
+
+	if (sample_id_all) {
+		void *data = &event->build_id.filename;
+		void *end = (void *)event + event->header.size;
+		size_t len = strnlen(data, end - data);
+
+		/* See comment in perf_event__comm_swap() */
+		if (len == (size_t)(end - data))
+			return -1;
+		data += PERF_ALIGN(len + 1, sizeof(u64));
+		swap_sample_id_all(event, data);
+	}
+	return 0;
+}
+
 static int perf_event__event_update_swap(union perf_event *event,
 					 bool sample_id_all __maybe_unused)
 {
@@ -1014,7 +1033,7 @@ static perf_event__swap_op perf_event__swap_ops[] = {
 	[PERF_RECORD_HEADER_ATTR]	  = perf_event__hdr_attr_swap,
 	[PERF_RECORD_HEADER_EVENT_TYPE]	  = perf_event__event_type_swap,
 	[PERF_RECORD_HEADER_TRACING_DATA] = perf_event__tracing_data_swap,
-	[PERF_RECORD_HEADER_BUILD_ID]	  = NULL,
+	[PERF_RECORD_HEADER_BUILD_ID]	  = perf_event__build_id_swap,
 	[PERF_RECORD_HEADER_FEATURE]	  = perf_event__header_feature_swap,
 	[PERF_RECORD_ID_INDEX]		  = perf_event__all64_swap,
 	[PERF_RECORD_AUXTRACE_INFO]	  = perf_event__auxtrace_info_swap,
@@ -2004,6 +2023,12 @@ static s64 perf_session__process_user_event(struct perf_session *session,
 		err = tool->tracing_data(tool, session, event);
 		break;
 	case PERF_RECORD_HEADER_BUILD_ID:
+		if (!perf_event__check_nul(event->build_id.filename,
+					   (void *)event + event->header.size,
+					   "HEADER_BUILD_ID")) {
+			err = 0;
+			break;
+		}
 		err = tool->build_id(tool, session, event);
 		break;
 	case PERF_RECORD_FINISHED_ROUND: