From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	sashiko-bot <sashiko-bot@kernel.org>,
	Ian Rogers <irogers@google.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12 1141/1376] perf dso: Use stored fd error instead of stale errno in file_read() and file_size()
Date: Sat, 12 Sep 2026 08:59:27 +0200
Message-ID: <20260912065632.988034517@linuxfoundation.org>
In-Reply-To: <20260912065607.535295758@linuxfoundation.org>
References: <20260912065607.535295758@linuxfoundation.org>
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6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

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

[ Upstream commit 075d2c32353ded0fe5f3b62f4aa4e98dccb3fb29 ]

file_read() and file_size() use ret = -errno when
dso__data(dso)->fd is negative after try_to_open_dso() fails.  By this
point errno has been through mutex_lock(), nsinfo__mountns_enter(), and
multiple open() attempts inside try_to_open_dso() — it no longer
reflects the actual open failure.  If errno happens to be 0, ret = 0
looks like EOF rather than an error, and file_size() callers like
dso__data_size() would then report a zero-sized file instead of
failing.

dso__data(dso)->fd is always negative on failure — -errno from
__open_dso() when no filename could be built (e.g. -EINVAL, -ENOENT),
or -1 when do_open() itself failed — and never 0, so use it directly
instead of reading the stale global errno.

No assert() or comment is needed after the assignment: the enclosing
if (dso__data(dso)->fd < 0) already guarantees ret < 0
[Namhyung Kim review].

Fixes: 33bdedcea2d7 ("perf tools: Protect dso cache fd with a mutex")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Reviewed-by: Ian Rogers <irogers@google.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/perf/util/dso.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 654a233326848..266f3b0a3a54b 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -963,7 +963,7 @@ static ssize_t file_read(struct dso *dso, struct machine *machine,
 
 	if (dso__data(dso)->fd < 0) {
 		dso__data(dso)->status = DSO_DATA_STATUS_ERROR;
-		ret = -errno;
+		ret = dso__data(dso)->fd;
 		goto out;
 	}
 
@@ -1086,8 +1086,8 @@ static int file_size(struct dso *dso, struct machine *machine)
 	try_to_open_dso(dso, machine);
 
 	if (dso__data(dso)->fd < 0) {
-		ret = -errno;
 		dso__data(dso)->status = DSO_DATA_STATUS_ERROR;
+		ret = dso__data(dso)->fd;
 		goto out;
 	}
 
-- 
2.53.0