ext4: avoid overlapping preallocations due to overflow

commit bedc5d3 upstream.

Let's say we want to allocate 2 blocks starting from 4294966386, after
predicting the file size, start is aligned to 4294965248, len is changed
to 2048, then end = start + size = 0x100000000. Since end is of
type ext4_lblk_t, i.e. uint, end is truncated to 0.

This causes (pa->pa_lstart >= end) to always hold when checking if the
current extent to be allocated crosses already preallocated blocks, so the
resulting ac_g_ex may cross already preallocated blocks. Hence we convert
the end type to loff_t and use pa_logical_end() to avoid overflow.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20230724121059.11834-4-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/ext4/mballoc.c

@@ -4022,8 +4022,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
 	struct ext4_super_block *es = sbi->s_es;
 	int bsbits, max;
-	ext4_lblk_t end;
-	loff_t size, start_off;
+	loff_t size, start_off, end;
 	loff_t orig_size __maybe_unused;
 	ext4_lblk_t start;
 	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
@@ -4131,7 +4130,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 	/* check we don't cross already preallocated blocks */
 	rcu_read_lock();
 	list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {
-		ext4_lblk_t pa_end;
+		loff_t pa_end;
 
 		if (pa->pa_deleted)
 			continue;
@@ -4141,8 +4140,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 			continue;
 		}
 
-		pa_end = pa->pa_lstart + EXT4_C2B(EXT4_SB(ac->ac_sb),
-						  pa->pa_len);
+		pa_end = pa_logical_end(EXT4_SB(ac->ac_sb), pa);
 
 		/* PA must not overlap original request */
 		BUG_ON(!(ac->ac_o_ex.fe_logical >= pa_end ||
@@ -4171,12 +4169,11 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 	/* XXX: extra loop to check we really don't overlap preallocations */
 	rcu_read_lock();
 	list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {
-		ext4_lblk_t pa_end;
+		loff_t pa_end;
 
 		spin_lock(&pa->pa_lock);
 		if (pa->pa_deleted == 0) {
-			pa_end = pa->pa_lstart + EXT4_C2B(EXT4_SB(ac->ac_sb),
-							  pa->pa_len);
+			pa_end = pa_logical_end(EXT4_SB(ac->ac_sb), pa);
 			BUG_ON(!(start >= pa_end || end <= pa->pa_lstart));
 		}
 		spin_unlock(&pa->pa_lock);