[PATCH 23/23] perf symbols: Add bounds checks to read_build_id() note iteration in minimal build

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

symbol-minimal.c's read_build_id() iterates ELF notes with the same
pattern as symbol-elf.c's elf_read_build_id(): pointer arithmetic
driven by n_namesz and n_descsz from 32-bit note header fields,
without validating that the name and desc fit within the note section
data.  A malformed ELF file with oversized note sizes causes
out-of-bounds reads past the section data buffer.

Add the same bounds check as the libelf path: validate namesz and
descsz individually against remaining data before advancing the
pointer, avoiding size_t overflow on 32-bit.

Fixes: b691f64360ecec49 ("perf symbols: Implement poor man's ELF parser")
Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Assisted-by: Claude Opus 4.6 <noreply@xxxxxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/symbol-minimal.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
index 8221dc9868f7c9f8..091071d06416e290 100644
--- a/tools/perf/util/symbol-minimal.c
+++ b/tools/perf/util/symbol-minimal.c
@@ -1,3 +1,4 @@
+#include "debug.h"
 #include "dso.h"
 #include "symbol.h"
 #include "symsrc.h"
@@ -44,7 +45,7 @@ static int read_build_id(void *note_data, size_t note_len, struct build_id *bid,
 	ptr = note_data;
 	while ((ptr + sizeof(*nhdr)) < (note_data + note_len)) {
 		const char *name;
-		size_t namesz, descsz;
+		size_t namesz, descsz, remaining;
 
 		nhdr = ptr;
 		if (need_swap) {
@@ -56,6 +57,14 @@ static int read_build_id(void *note_data, size_t note_len, struct build_id *bid,
 		namesz = NOTE_ALIGN(nhdr->n_namesz);
 		descsz = NOTE_ALIGN(nhdr->n_descsz);
 
+		/* validate individually to avoid size_t overflow on 32-bit */
+		remaining = note_data + note_len - ptr - sizeof(*nhdr);
+		if (namesz > remaining || descsz > remaining - namesz) {
+			pr_warning("%s: oversized note: n_namesz=%u, n_descsz=%u\n",
+				   __func__, nhdr->n_namesz, nhdr->n_descsz);
+			break;
+		}
+
 		ptr += sizeof(*nhdr);
 		name = ptr;
 		ptr += namesz;
-- 
2.54.0