udf: Fix regression in UDF anchor block detection

In some cases it could happen that some block passed test in
udf_check_anchor_block() even though udf_read_tagged() refused to read it later
(e.g. because checksum was not correct).  This patch makes
udf_check_anchor_block() use udf_read_tagged() so that the checking is
stricter.

This fixes the regression (certain disks unmountable) caused by commit
423cf6dc04eb79d441bfda2b127bc4b57134b41d.

Signed-off-by: Tomas Janousek <tomi@nomi.cz>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 23 insertions, 34 deletions

diff --git a/fs/udf/super.c b/fs/udf/super.c
index 7a5f69be6ac2..44cc702f96cc 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -682,38 +682,26 @@ static int udf_vrs(struct super_block *sb, int silent)
 /*
  * Check whether there is an anchor block in the given block
  */
-static int udf_check_anchor_block(struct super_block *sb, sector_t block,
-                                        bool varconv)
+static int udf_check_anchor_block(struct super_block *sb, sector_t block)
 {
-        struct buffer_head *bh = NULL;
-        tag *t;
+        struct buffer_head *bh;
         uint16_t ident;
-        uint32_t location;
 
-        if (varconv) {
-                if (udf_fixed_to_variable(block) >=
-                    sb->s_bdev->bd_inode->i_size >> sb->s_blocksize_bits)
-                        return 0;
-                bh = sb_bread(sb, udf_fixed_to_variable(block));
-        }
-        else
-                bh = sb_bread(sb, block);
+        if (UDF_QUERY_FLAG(sb, UDF_FLAG_VARCONV) &&
+            udf_fixed_to_variable(block) >=
+            sb->s_bdev->bd_inode->i_size >> sb->s_blocksize_bits)
+                return 0;
 
+        bh = udf_read_tagged(sb, block, block, &ident);
         if (!bh)
                 return 0;
-
-        t = (tag *)bh->b_data;
-        ident = le16_to_cpu(t->tagIdent);
-        location = le32_to_cpu(t->tagLocation);
         brelse(bh);
-        if (ident != TAG_IDENT_AVDP)
-                return 0;
-        return location == block;
+
+        return ident == TAG_IDENT_AVDP;
 }
 
 /* Search for an anchor volume descriptor pointer */
-static sector_t udf_scan_anchors(struct super_block *sb, bool varconv,
-                                        sector_t lastblock)
+static sector_t udf_scan_anchors(struct super_block *sb, sector_t lastblock)
 {
         sector_t last[6];
         int i;
@@ -739,7 +727,7 @@ static sector_t udf_scan_anchors(struct super_block *sb, bool varconv,
                                 sb->s_blocksize_bits)
                         continue;
 
-                if (udf_check_anchor_block(sb, last[i], varconv)) {
+                if (udf_check_anchor_block(sb, last[i])) {
                         sbi->s_anchor[0] = last[i];
                         sbi->s_anchor[1] = last[i] - 256;
                         return last[i];
@@ -748,17 +736,17 @@ static sector_t udf_scan_anchors(struct super_block *sb, bool varconv,
                 if (last[i] < 256)
                         continue;
 
-                if (udf_check_anchor_block(sb, last[i] - 256, varconv)) {
+                if (udf_check_anchor_block(sb, last[i] - 256)) {
                         sbi->s_anchor[1] = last[i] - 256;
                         return last[i];
                 }
         }
 
-        if (udf_check_anchor_block(sb, sbi->s_session + 256, varconv)) {
+        if (udf_check_anchor_block(sb, sbi->s_session + 256)) {
                 sbi->s_anchor[0] = sbi->s_session + 256;
                 return last[0];
         }
-        if (udf_check_anchor_block(sb, sbi->s_session + 512, varconv)) {
+        if (udf_check_anchor_block(sb, sbi->s_session + 512)) {
                 sbi->s_anchor[0] = sbi->s_session + 512;
                 return last[0];
         }
@@ -780,23 +768,24 @@ static void udf_find_anchor(struct super_block *sb)
         int i;
         struct udf_sb_info *sbi = UDF_SB(sb);
 
-        lastblock = udf_scan_anchors(sb, 0, sbi->s_last_block);
+        lastblock = udf_scan_anchors(sb, sbi->s_last_block);
         if (lastblock)
                 goto check_anchor;
 
         /* No anchor found? Try VARCONV conversion of block numbers */
+        UDF_SET_FLAG(sb, UDF_FLAG_VARCONV);
         /* Firstly, we try to not convert number of the last block */
-        lastblock = udf_scan_anchors(sb, 1,
+        lastblock = udf_scan_anchors(sb,
                                 udf_variable_to_fixed(sbi->s_last_block));
-        if (lastblock) {
-                UDF_SET_FLAG(sb, UDF_FLAG_VARCONV);
+        if (lastblock)
                 goto check_anchor;
-        }
 
         /* Secondly, we try with converted number of the last block */
-        lastblock = udf_scan_anchors(sb, 1, sbi->s_last_block);
-        if (lastblock)
-                UDF_SET_FLAG(sb, UDF_FLAG_VARCONV);
+        lastblock = udf_scan_anchors(sb, sbi->s_last_block);
+        if (!lastblock) {
+                /* VARCONV didn't help. Clear it. */
+                UDF_CLEAR_FLAG(sb, UDF_FLAG_VARCONV);
+        }
 
 check_anchor:
         /*