Subject: [PATCH AUTOSEL 5.4 193/350] libbpf: Fix error handling in bpf_map__reuse_fd()

From: Sasha Levin <[email-masked]>
Date: Tue, 10 Dec 2019 16:04:58 -0500

From: Toke Høiland-Jørgensen <[email-masked]>

[ Upstream commit d1b4574a4b86565325ef2e545eda8dfc9aa07c60 ]

bpf_map__reuse_fd() was calling close() in the error path before returning
an error value based on errno. However, close can change errno, so that can
lead to potentially misleading error messages. Instead, explicitly store
errno in the err variable before each goto.

Signed-off-by: Toke Høiland-Jørgensen <[email-masked]>
Signed-off-by: Alexei Starovoitov <[email-masked]>
Acked-by: Andrii Nakryiko <[email-masked]>
Link: https://lore.kernel.org/bpf/[email-masked]
Signed-off-by: Sasha Levin <[email-masked]>
---
 tools/lib/bpf/libbpf.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e0276520171b9..a267cd0c0ce28 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1897,16 +1897,22 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 		return -errno;
 
 	new_fd = open("/", O_RDONLY | O_CLOEXEC);
-	if (new_fd < 0)
+	if (new_fd < 0) {
+		err = -errno;
 		goto err_free_new_name;
+	}
 
 	new_fd = dup3(fd, new_fd, O_CLOEXEC);
-	if (new_fd < 0)
+	if (new_fd < 0) {
+		err = -errno;
 		goto err_close_new_fd;
+	}
 
 	err = zclose(map->fd);
-	if (err)
+	if (err) {
+		err = -errno;
 		goto err_close_new_fd;
+	}
 	free(map->name);
 
 	map->fd = new_fd;
@@ -1925,7 +1931,7 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 	close(new_fd);
 err_free_new_name:
 	free(new_name);
-	return -errno;
+	return err;
 }
 
 int bpf_map__resize(struct bpf_map *map, __u32 max_entries)
-- 
2.20.1