[Patch] lib/sysfs.c: check if cxt->dir_path is NULL in sysfs_readlink()

[Cong Wang <amwang@xxxxxxxxxx>]

From: Cong Wang <xiyou.wangcong@xxxxxxxxx>

cxt->dir_path could be NULL, for example, when sysfs_init() fails,
check this before calling readlink()/readlink_at().

Cc: Karel Zak <kzak@xxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>

---
diff --git a/lib/sysfs.c b/lib/sysfs.c
index 312191f..b4fb7cd 100644
--- a/lib/sysfs.c
+++ b/lib/sysfs.c
@@ -220,6 +220,9 @@ static int sysfs_open(struct sysfs_cxt *cxt, const char *attr)
 ssize_t sysfs_readlink(struct sysfs_cxt *cxt, const char *attr,
 		   char *buf, size_t bufsiz)
 {
+	if (!cxt->dir_path)
+		return -1;
+
 	if (attr)
 		return readlink_at(cxt->dir_fd, cxt->dir_path, attr, buf, bufsiz);
 
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