[PATCH 05/12] perf jitdump: Check snprintf return before computing header size

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

snprintf() returns the would-have-been length on truncation.  When the
jitted filename exceeds PATH_MAX, the unclamped 'size' value inflates
sizeof(event->mmap2.filename) - size into a massive underflow, causing
the header.size computation to write an oversized header.  The
subsequent write to 'id = event + header.size - idr_size' then corrupts
the heap.

Clamp size to PATH_MAX - 1 after snprintf in both jit_repipe_code_load()
and jit_repipe_code_move().

Fixes: 9b07e27f88b9 ("perf inject: Add jitdump mmap injection support")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/jitdump.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index 078d3304d2b7ebce..fd11e07bf00b7978 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -493,6 +493,9 @@ static int jit_repipe_code_load(struct jit_buf_desc *jd, union jr_entry *jr)
 			jd->dir,
 			nspid,
 			count);
+	/* snprintf returns would-be length on truncation, clamp to buffer */
+	if (size >= PATH_MAX)
+		size = PATH_MAX - 1;
 
 	size++; /* for \0 */
 
@@ -623,6 +626,9 @@ static int jit_repipe_code_move(struct jit_buf_desc *jd, union jr_entry *jr)
 	         jd->dir,
 		 nspid,
 		 jr->move.code_index);
+	/* snprintf returns would-be length on truncation, clamp to buffer */
+	if (size >= PATH_MAX)
+		size = PATH_MAX - 1;
 
 	size++; /* for \0 */
 
-- 
2.55.0