[PATCH v3 6/6] xfs: assert the reservation covers each da fork growth

[Javier Tia <javier@peridio.com>]

xfs_da_grow_inode_int() subtracts the blocks it just allocated from
args->total, the caller's remaining block reservation.  The subtraction
is unsigned, so a caller that reaches it with too small a total wraps
the field instead of failing, and every allocation afterwards runs with
a bogus reservation.  Assert the remaining reservation still covers the
step, so an under-reserved or uninitialised total trips in debug builds
instead of silently wrapping.

Suggested-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Javier Tia <floss@jetm.me>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
---
 fs/xfs/libxfs/xfs_da_btree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
index ad801b7bd2dd..9be407affc6e 100644
--- a/fs/xfs/libxfs/xfs_da_btree.c
+++ b/fs/xfs/libxfs/xfs_da_btree.c
@@ -2385,6 +2385,7 @@ xfs_da_grow_inode_int(
 	}
 
 	/* account for newly allocated blocks in reserved blocks total */
+	ASSERT(args->total >= dp->i_nblocks - nblks);
 	args->total -= dp->i_nblocks - nblks;
 
 out_free_map:
-- 
Javier Tia