From: Theodore Ts'o <tytso@mit.edu>
Date: Tue, 9 Aug 2022 14:52:57 +0000 (-0400)
Subject: e2fsck: fix potential fencepost error in e2fsck_should_rebuild_extents()
X-Git-Tag: v1.46.6-rc1~39
X-Git-Url: https://git.whamcloud.com/?a=commitdiff_plain;h=7464397a0c5df0416a7ef3436747045b36fb7882;p=tools%2Fe2fsprogs.git

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
--- 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
--- 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;