udf: Add checks to not underflow sector_t

Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/udf/super.c b/fs/udf/super.c
index b9dc6adfdd2d3e5cc9e307bc73258bb6109930d9..3c2d35dc2577fc4282d268fdea19fd0cbc89244b 100644 (file)
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -731,13 +731,18 @@ static sector_t udf_scan_anchors(struct super_block *sb, sector_t lastblock)
        sector_t last[6];
        int i;
        struct udf_sb_info *sbi = UDF_SB(sb);
-
-       last[0] = lastblock;
-       last[1] = last[0] - 1;
-       last[2] = last[0] + 1;
-       last[3] = last[0] - 2;
-       last[4] = last[0] - 150;
-       last[5] = last[0] - 152;
+       int last_count = 0;
+
+       last[last_count++] = lastblock;
+       if (lastblock >= 1)
+               last[last_count++] = lastblock - 1;
+       last[last_count++] = lastblock + 1;
+       if (lastblock >= 2)
+               last[last_count++] = lastblock - 2;
+       if (lastblock >= 150)
+               last[last_count++] = lastblock - 150;
+       if (lastblock >= 152)
+               last[last_count++] = lastblock - 152;
 
        /*  according to spec, anchor is in either:
         *     block 256
@@ -745,7 +750,7 @@ static sector_t udf_scan_anchors(struct super_block *sb, sector_t lastblock)
         *     lastblock
         *  however, if the disc isn't closed, it could be 512 */
 
-       for (i = 0; i < ARRAY_SIZE(last); i++) {
+       for (i = 0; i < last_count; i++) {
                if (last[i] >= sb->s_bdev->bd_inode->i_size >>
                                sb->s_blocksize_bits)
                        continue;