[03/14] libmultipath: sysfs_bin_attr_get_value(): no error if buffer is filled

Commit Message

Martin Wilck July 6, 2022, 2:38 p.m. UTC

From: Martin Wilck <[e-mail]>

sysfs_bin_attr_get_value() sets the length of bytes read to 0
when the provided buffer was too small, truncating potentially
useful data. This is harmful e.g. in do_inquiry(), if the "inquiry"
sysfs attribute contains more than 96 bytes (which is possible).

Actually, binary attributes don't need to be 0-terminated. Thus,
unlike for string attributes, it's not an error if the requested number of
bytes is exactly equal to the number of bytes read. We expect that
the caller knows how many bytes it needs to read.

Signed-off-by: Martin Wilck <[e-mail]>
---
 libmultipath/discovery.c | 10 ++++++----
 libmultipath/sysfs.c     |  5 +----
 2 files changed, 7 insertions(+), 8 deletions(-)

Patch

diff --git a/libmultipath/discovery.c b/libmultipath/discovery.c
index 7e09e4e..f5b8401 100644
--- a/libmultipath/discovery.c
+++ b/libmultipath/discovery.c
@@ -1341,13 +1341,15 @@  static int
 get_vpd_sysfs (struct udev_device *parent, int pg, char * str, int maxlen)
 {
 	int len;
-	size_t buff_len;
+	ssize_t buff_len;
 	unsigned char buff[VPD_BUFLEN];
 
 	memset(buff, 0x0, VPD_BUFLEN);
-	if (!parent || sysfs_get_vpd(parent, pg, buff, VPD_BUFLEN) <= 0) {
-		condlog(3, "failed to read sysfs vpd pg%02x", pg);
-		return -EINVAL;
+	buff_len = sysfs_get_vpd(parent, pg, buff, VPD_BUFLEN);
+	if (buff_len < 0) {
+		condlog(3, "failed to read sysfs vpd pg%02x: %s",
+			pg, strerror(-buff_len));
+		return buff_len;
 	}
 
 	if (buff[1] != pg) {
diff --git a/libmultipath/sysfs.c b/libmultipath/sysfs.c
index f45dbee..3ec9251 100644
--- a/libmultipath/sysfs.c
+++ b/libmultipath/sysfs.c
@@ -146,10 +146,7 @@  ssize_t sysfs_bin_attr_get_value(struct udev_device *dev, const char *attr_name,
 	if (size < 0) {
 		condlog(4, "read from %s failed: %s", devpath, strerror(errno));
 		size = -errno;
-	} else if (size == (ssize_t)value_len) {
-		condlog(4, "overflow while reading from %s", devpath);
-		size = 0;
-	}
+	};
 
 	close(fd);
 	return size;