[PATCH 3/4] ext4: avoid overlapping preallocations due to overflow

[Baokun Li]

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_end() to avoid overflow.

Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
 fs/ext4/mballoc.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 2090e5e7ba58..77d47af525d9 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4222,12 +4222,13 @@ ext4_mb_pa_rb_next_iter(ext4_lblk_t new_start, ext4_lblk_t cur_start, struct rb_
 
 static inline void
 ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
-			  ext4_lblk_t start, ext4_lblk_t end)
+			  ext4_lblk_t start, loff_t end)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
 	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
 	struct ext4_prealloc_space *tmp_pa;
-	ext4_lblk_t tmp_pa_start, tmp_pa_end;
+	ext4_lblk_t tmp_pa_start;
+	loff_t tmp_pa_end;
 	struct rb_node *iter;
 
 	read_lock(&ei->i_prealloc_lock);
@@ -4236,7 +4237,7 @@ ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
 		tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
 				  pa_node.inode_node);
 		tmp_pa_start = tmp_pa->pa_lstart;
-		tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
+		tmp_pa_end = pa_end(sbi, tmp_pa);
 
 		spin_lock(&tmp_pa->pa_lock);
 		if (tmp_pa->pa_deleted == 0)
@@ -4258,14 +4259,14 @@ ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
  */
 static inline void
 ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
-			  ext4_lblk_t *start, ext4_lblk_t *end)
+			  ext4_lblk_t *start, loff_t *end)
 {
 	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
 	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
 	struct ext4_prealloc_space *tmp_pa = NULL, *left_pa = NULL, *right_pa = NULL;
 	struct rb_node *iter;
-	ext4_lblk_t new_start, new_end;
-	ext4_lblk_t tmp_pa_start, tmp_pa_end, left_pa_end = -1, right_pa_start = -1;
+	ext4_lblk_t new_start, tmp_pa_start, right_pa_start = -1;
+	loff_t new_end, tmp_pa_end, left_pa_end = -1;
 
 	new_start = *start;
 	new_end = *end;
@@ -4284,7 +4285,7 @@ ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
 		tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
 				  pa_node.inode_node);
 		tmp_pa_start = tmp_pa->pa_lstart;
-		tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
+		tmp_pa_end = pa_end(sbi, tmp_pa);
 
 		/* PA must not overlap original request */
 		spin_lock(&tmp_pa->pa_lock);
@@ -4364,8 +4365,7 @@ ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
 	}
 
 	if (left_pa) {
-		left_pa_end =
-			left_pa->pa_lstart + EXT4_C2B(sbi, left_pa->pa_len);
+		left_pa_end = pa_end(sbi, left_pa);
 		BUG_ON(left_pa_end > ac->ac_o_ex.fe_logical);
 	}
 
@@ -4404,8 +4404,7 @@ 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;
 
-- 
2.31.1