ext4: add two helper functions fex_end() and pa_end()

When we use lstart + len to calculate the end of free extent or prealloc
space, it may exceed the maximum value of 4294967295(0xffffffff) supported
by ext4_lblk_t and cause overflow, which may lead to various problems.

Therefore, we add two helper functions, fex_end() and pa_end(), to limit
the type of end to loff_t, and also convert lstart to loff_t for
calculation to avoid overflow.

Signed-off-by: Baokun Li <[email protected]>

Author: LiBaokun96

fs/ext4/mballoc.c

@@ -4428,7 +4428,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 
 	/* first, let's learn actual file size
 	 * given current request is allocated */
-	size = ac->ac_o_ex.fe_logical + EXT4_C2B(sbi, ac->ac_o_ex.fe_len);
+	size = fex_end(sbi, &ac->ac_o_ex, NULL);
 	size = size << bsbits;
 	if (size < i_size_read(ac->ac_inode))
 		size = i_size_read(ac->ac_inode);
@@ -5661,7 +5661,7 @@ static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
 
 	group_pa_eligible = sbi->s_mb_group_prealloc > 0;
 	inode_pa_eligible = true;
-	size = ac->ac_o_ex.fe_logical + EXT4_C2B(sbi, ac->ac_o_ex.fe_len);
+	size = fex_end(sbi, &ac->ac_o_ex, NULL);
 	isize = (i_size_read(ac->ac_inode) + ac->ac_sb->s_blocksize - 1)
 		>> bsbits;
 

fs/ext4/mballoc.h

@@ -233,6 +233,19 @@ static inline ext4_fsblk_t ext4_grp_offs_to_block(struct super_block *sb,
 		(fex->fe_start << EXT4_SB(sb)->s_cluster_bits);
 }
 
+static inline loff_t fex_end(struct ext4_sb_info *sbi,
+			     struct ext4_free_extent *fex, ext4_grpblk_t *fe_len)
+{
+	return (loff_t)fex->fe_logical +
+		EXT4_C2B(sbi, fe_len ? *fe_len : fex->fe_len);
+}
+
+static inline loff_t pa_end(struct ext4_sb_info *sbi,
+			    struct ext4_prealloc_space *pa)
+{
+	return (loff_t)pa->pa_lstart + EXT4_C2B(sbi, pa->pa_len);
+}
+
 typedef int (*ext4_mballoc_query_range_fn)(
 	struct super_block		*sb,
 	ext4_group_t			agno,