[PATCH 2/4] perf header: Use write lock when translating BPF prog info pointers

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

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

write_bpf_prog_info() holds a read lock while temporarily mutating
info_linear via bpil_addr_to_offs()/bpil_offs_to_addr().  Between these
two calls, the pointers in info_linear contain file offsets instead of
heap addresses.  Concurrent readers holding the same read lock see the
file offsets and dereference them as pointers.

Use down_write()/up_write() instead of down_read()/up_read() to exclude
concurrent readers during the addr-to-offset-to-addr translation window.

Fixes: 63ac7968a1fb ("perf bpf: Save bpf_prog_info information as headers to perf.data")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/header.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index e90e541f546b4537..7db7da090a1e0c78 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1120,7 +1120,8 @@ static int write_bpf_prog_info(struct feat_fd *ff  __maybe_unused,
 	struct rb_node *next;
 	int ret = 0;
 
-	down_read(&env->bpf_progs.lock);
+	/* write lock: bpil_addr_to_offs() temporarily mutates info_linear */
+	down_write(&env->bpf_progs.lock);
 
 	ret = do_write(ff, &env->bpf_progs.infos_cnt,
 		       sizeof(env->bpf_progs.infos_cnt));
@@ -1150,7 +1151,7 @@ static int write_bpf_prog_info(struct feat_fd *ff  __maybe_unused,
 			goto out;
 	}
 out:
-	up_read(&env->bpf_progs.lock);
+	up_write(&env->bpf_progs.lock);
 	return ret;
 #else
 	pr_err("ERROR: Trying to write bpf_prog_info without libbpf support.\n");
-- 
2.55.0