ext4: Extent overlap bugfix

This patch adds a check for overlap of extents and cuts short the
new extent to be inserted, if there is a chance of overlap.

Signed-off-by: Amit Arora <aarora@in.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 58 insertions, 2 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 1630317817b8..03c777abf01f 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1128,6 +1128,55 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
 }
 
 /*
+ * check if a portion of the "newext" extent overlaps with an
+ * existing extent.
+ *
+ * If there is an overlap discovered, it updates the length of the newext
+ * such that there will be no overlap, and then returns 1.
+ * If there is no overlap found, it returns 0.
+ */
+unsigned int ext4_ext_check_overlap(struct inode *inode,
+                                    struct ext4_extent *newext,
+                                    struct ext4_ext_path *path)
+{
+        unsigned long b1, b2;
+        unsigned int depth, len1;
+        unsigned int ret = 0;
+
+        b1 = le32_to_cpu(newext->ee_block);
+        len1 = le16_to_cpu(newext->ee_len);
+        depth = ext_depth(inode);
+        if (!path[depth].p_ext)
+                goto out;
+        b2 = le32_to_cpu(path[depth].p_ext->ee_block);
+
+        /*
+         * get the next allocated block if the extent in the path
+         * is before the requested block(s) 
+         */
+        if (b2 < b1) {
+                b2 = ext4_ext_next_allocated_block(path);
+                if (b2 == EXT_MAX_BLOCK)
+                        goto out;
+        }
+
+        /* check for wrap through zero */
+        if (b1 + len1 < b1) {
+                len1 = EXT_MAX_BLOCK - b1;
+                newext->ee_len = cpu_to_le16(len1);
+                ret = 1;
+        }
+
+        /* check for overlap */
+        if (b1 + len1 > b2) {
+                newext->ee_len = cpu_to_le16(b2 - b1);
+                ret = 1;
+        }
+out:
+        return ret;
+}
+
+/*
  * ext4_ext_insert_extent:
  * tries to merge requsted extent into the existing extent or
  * inserts requested extent as new one into the tree,
@@ -2031,7 +2080,15 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
 
         /* allocate new block */
         goal = ext4_ext_find_goal(inode, path, iblock);
-        allocated = max_blocks;
+
+        /* Check if we can really insert (iblock)::(iblock+max_blocks) extent */
+        newex.ee_block = cpu_to_le32(iblock);
+        newex.ee_len = cpu_to_le16(max_blocks);
+        err = ext4_ext_check_overlap(inode, &newex, path);
+        if (err)
+                allocated = le16_to_cpu(newex.ee_len);
+        else
+                allocated = max_blocks;
         newblock = ext4_new_blocks(handle, inode, goal, &allocated, &err);
         if (!newblock)
                 goto out2;
@@ -2039,7 +2096,6 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
                         goal, newblock, allocated);
 
         /* try to insert new extent into found leaf and return */
-        newex.ee_block = cpu_to_le32(iblock);
         ext4_ext_store_pblock(&newex, newblock);
         newex.ee_len = cpu_to_le16(allocated);
         err = ext4_ext_insert_extent(handle, inode, path, &newex);