e2fsck: fix potential fencepost error in e2fsck_should_rebuild_extents()

The ext2_extent_info.max_depth is zero-based (e.g., it is zero when
the entire extent tree fits in the inode).  Hence, if it is equal to
MAX_EXTENT_DEPTH_COUNT we should always rebuild the extent tree to
shorten it.

Also, for 1k block file systems, it's possible for the worst-case
extent tree in its most compact form to have a maximum depth of 6, not
5.  So set MAX_EXTENT_DEPTH_COUNT to 8 just to be sure we have plenty
of headroom.  (The kernel supports an extent depth up to 2**16, but
e2fsck only keeps statistics up to MAX_EXTENT_DEPTH_COUNT, and if it's
deeper than that, we know that it will be profitable to rebuild the
extent tree in any case.)

Addresses-Coverity-Bug: 1507761
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/e2fsck/e2fsck.h b/e2fsck/e2fsck.h
index 00b2091..75baf2c 100644 (file)
--- a/e2fsck/e2fsck.h
+++ b/e2fsck/e2fsck.h
@@ -233,7 +233,7 @@ typedef struct ea_refcount *ext2_refcount_t;
  */
 typedef struct e2fsck_struct *e2fsck_t;
 
-#define MAX_EXTENT_DEPTH_COUNT 5
+#define MAX_EXTENT_DEPTH_COUNT 8
 
 /*
  * This strucutre is used to manage the list of extents in a file. Placing

diff --git a/e2fsck/extents.c b/e2fsck/extents.c
index 86fe00e..70798f3 100644 (file)
--- a/e2fsck/extents.c
+++ b/e2fsck/extents.c
@@ -583,7 +583,7 @@ errcode_t e2fsck_should_rebuild_extents(e2fsck_t ctx,
                            sizeof(struct ext3_extent);
 
        /* If the extent tree is too deep, then rebuild it. */
-       if (info->max_depth > MAX_EXTENT_DEPTH_COUNT) {
+       if (info->max_depth > MAX_EXTENT_DEPTH_COUNT-1) {
                pctx->blk = info->max_depth;
                op = PR_1E_CAN_COLLAPSE_EXTENT_TREE;
                goto rebuild;