[PATCH 01/12] perf jitdump: Fix extended header read that always fails

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

jit_open() sets bsz = bs before the fread() that uses bs - bsz as the
read size, making the expression always evaluate to zero.  fread() with
size 0 returns 0, which triggers the ret != 1 error path — so extended
jitdump headers (total_size > sizeof(header)) have been silently broken
since the original implementation.

Additionally, when 0 < bs <= bsz the if (bs > bsz) block is skipped
entirely, leaving extended header bytes unread in the stream.  Subsequent
jit_get_next_entry() calls then parse those leftover bytes as a
jr_prefix, corrupting the record stream.

Fix by separating the buffer growth from the read: realloc only when
bs > bsz, then unconditionally fread bs bytes when bs > 0.

Fixes: 9b07e27f88b9cd78 ("perf inject: Add jitdump mmap injection support")
Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/jitdump.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index 83005b30b9bf3fd7..4b7c7ba7cd95ddbb 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -224,10 +224,12 @@ jit_open(struct jit_buf_desc *jd, const char *name)
 		n = realloc(buf, bs);
 		if (!n)
 			goto error;
-		bsz = bs;
 		buf = n;
-		/* read extra we do not know about */
-		ret = fread(buf, bs - bsz, 1, jd->in);
+		bsz = bs;
+	}
+	if (bs > 0) {
+		/* consume extended header bytes from the stream */
+		ret = fread(buf, bs, 1, jd->in);
 		if (ret != 1)
 			goto error;
 	}
-- 
2.55.0