Comment 1 for bug 1164683

diff --git a/AUTHORS b/AUTHORS
index f29f9a3..54fe7ce 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -385,5 +385,6 @@ CONTRIBUTORS:
       Yoshihiro Takahashi <email address hidden>
       Yuri Chornoivan <email address hidden>
       Yu Zhiguo <email address hidden>
+ Zachary Catlin <email address hidden>
       Zdenek Behan <email address hidden>
       Zhi Li <email address hidden>
diff --git a/libblkid/src/superblocks/udf.c b/libblkid/src/superblocks/udf.c
index 2cb471d..c9fb022 100644
--- a/libblkid/src/superblocks/udf.c
+++ b/libblkid/src/superblocks/udf.c
@@ -64,17 +64,25 @@ static int probe_udf(blkid_probe pr,
        struct volume_descriptor *vd;
        struct volume_structure_descriptor *vsd;
        unsigned int bs;
+ unsigned int pbs[2];
        unsigned int b;
        unsigned int type;
        unsigned int count;
        unsigned int loc;
+ unsigned int i;

- /* search Volume Sequence Descriptor (VSD) to get the logical
- * block size of the volume */
- for (bs = 0x800; bs < 0x8000; bs += 0x800) {
+ /* The block size of a UDF filesystem is that of the underlying
+ * storage; we check later on for the special case of image files,
+ * which may have the 2048-byte block size of optical media. */
+ pbs[0] = blkid_probe_get_sectorsize(pr);
+ pbs[1] = 0x800;
+
+ /* check for a Volume Structure Descriptor (VSD); each is
+ * 2048 bytes long */
+ for (b = 0; b < 0x8000; b += 0x800) {
                vsd = (struct volume_structure_descriptor *)
                        blkid_probe_get_buffer(pr,
- UDF_VSD_OFFSET + bs,
+ UDF_VSD_OFFSET + b,
                                        sizeof(*vsd));
                if (!vsd)
                        return 1;
@@ -88,7 +96,7 @@ static int probe_udf(blkid_probe pr,
        for (b = 0; b < 64; b++) {
                vsd = (struct volume_structure_descriptor *)
                        blkid_probe_get_buffer(pr,
- UDF_VSD_OFFSET + ((blkid_loff_t) b * bs),
+ UDF_VSD_OFFSET + ((blkid_loff_t) b * 0x800),
                                        sizeof(*vsd));
                if (!vsd)
                        return -1;
@@ -102,17 +110,24 @@ static int probe_udf(blkid_probe pr,
        return -1;

 anchor:
- /* read Anchor Volume Descriptor (AVDP) */
- vd = (struct volume_descriptor *)
- blkid_probe_get_buffer(pr, 256 * bs, sizeof(*vd));
- if (!vd)
- return -1;
-
- type = le16_to_cpu(vd->tag.id);
- if (type != 2) /* TAG_ID_AVDP */
- return 0;
+ /* read Anchor Volume Descriptor (AVDP), checking block size */
+ for (i = 0; i < 2; i++) {
+ vd = (struct volume_descriptor *)
+ blkid_probe_get_buffer(pr, 256 * pbs[i], sizeof(*vd));
+ if (!vd)
+ return -1;
+
+ type = le16_to_cpu(vd->tag.id);
+ if (type == 2) /* TAG_ID_AVDP */
+ goto real_blksz;
+ }
+ return 0;
+
+real_blksz:
+ /* Use the actual block size from here on out */
+ bs = pbs[i];

- /* get desriptor list address and block count */
+ /* get descriptor list address and block count */
        count = le32_to_cpu(vd->type.anchor.length) / bs;
        loc = le32_to_cpu(vd->type.anchor.location);