[PATCH 9/9] perf dso: Set standard errno on decompression failure

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

dso__get_filename() sets errno to a negative custom DSO_LOAD_ERRNO
value when kernel module decompression fails:

  errno = *dso__load_errno(dso);  /* e.g. -9996 */

The caller __open_dso() then computes fd = -errno, producing a large
positive value (9996) that looks like a valid file descriptor.  This
can cause close_data_fd() to close an unrelated fd used by another
subsystem.

Set errno to EIO instead.  The detailed error code is already stored
in dso__load_errno(dso) for diagnostic messages.

Fixes: 1d6b3c9ba756a513 ("perf tools: Decompress kernel module when reading DSO data")
Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Assisted-by: Claude <noreply@xxxxxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/dso.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 79f1a30f3683d6b3..2309196d8df3111c 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -600,7 +600,13 @@ static char *dso__get_filename(struct dso *dso, const char *root_dir,
 		size_t len = sizeof(newpath);
 
 		if (dso__decompress_kmodule_path(dso, name, newpath, len) < 0) {
-			errno = *dso__load_errno(dso);
+			/*
+			 * Use a standard errno value, not the negative custom
+			 * DSO_LOAD_ERRNO stored in dso__load_errno(dso):
+			 * __open_dso() computes fd = -errno, so a negative
+			 * errno produces a positive fd that looks valid.
+			 */
+			errno = EIO;
 			goto out;
 		}
 
-- 
2.54.0