f2fs: enhance sanity_check_raw_super() to avoid potential overflows

In order to avoid the below overflow issue, we should have checked the
boundaries in superblock before reaching out to allocation. As Linus suggested,
the right place should be sanity_check_raw_super().

Dr Silvio Cesare of InfoSect reported:

There are integer overflows with using the cp_payload superblock field in the
f2fs filesystem potentially leading to memory corruption.

include/linux/f2fs_fs.h

struct f2fs_super_block {
...
        __le32 cp_payload;

fs/f2fs/f2fs.h

typedef u32 block_t;    /*
                         * should not change u32, since it is the on-disk block
                         * address format, __le32.
                         */
...

static inline block_t __cp_payload(struct f2fs_sb_info *sbi)
{
        return le32_to_cpu(F2FS_RAW_SUPER(sbi)->cp_payload);
}

fs/f2fs/checkpoint.c

        block_t start_blk, orphan_blocks, i, j;
...
        start_blk = __start_cp_addr(sbi) + 1 + __cp_payload(sbi);
        orphan_blocks = __start_sum_addr(sbi) - 1 - __cp_payload(sbi);

+++ integer overflows

...
        unsigned int cp_blks = 1 + __cp_payload(sbi);
...
        sbi->ckpt = kzalloc(cp_blks * blk_size, GFP_KERNEL);

+++ integer overflow leading to incorrect heap allocation.

        int cp_payload_blks = __cp_payload(sbi);
...
        ckpt->cp_pack_start_sum = cpu_to_le32(1 + cp_payload_blks +
                        orphan_blocks);

+++ sign bug and integer overflow

...
        for (i = 1; i < 1 + cp_payload_blks; i++)

+++ integer overflow

...

      sbi->max_orphans = (sbi->blocks_per_seg - F2FS_CP_PACKS -
                        NR_CURSEG_TYPE - __cp_payload(sbi)) *
                                F2FS_ORPHANS_PER_BLOCK;

+++ integer overflow
Reported-by: Greg KH <greg@kroah.com>
Reported-by: Silvio Cesare <silvio.cesare@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -2139,6 +2139,8 @@ static inline bool sanity_check_area_boundary(struct f2fs_sb_info *sbi,
 static int sanity_check_raw_super(struct f2fs_sb_info *sbi,
 				struct buffer_head *bh)
 {
+	block_t segment_count, segs_per_sec, secs_per_zone;
+	block_t total_sections, blocks_per_seg;
 	struct f2fs_super_block *raw_super = (struct f2fs_super_block *)
 					(bh->b_data + F2FS_SUPER_OFFSET);
 	struct super_block *sb = sbi->sb;
@@ -2195,6 +2197,72 @@ static int sanity_check_raw_super(struct f2fs_sb_info *sbi,
 		return 1;
 	}
 
+	segment_count = le32_to_cpu(raw_super->segment_count);
+	segs_per_sec = le32_to_cpu(raw_super->segs_per_sec);
+	secs_per_zone = le32_to_cpu(raw_super->secs_per_zone);
+	total_sections = le32_to_cpu(raw_super->section_count);
+
+	/* blocks_per_seg should be 512, given the above check */
+	blocks_per_seg = 1 << le32_to_cpu(raw_super->log_blocks_per_seg);
+
+	if (segment_count > F2FS_MAX_SEGMENT ||
+				segment_count < F2FS_MIN_SEGMENTS) {
+		f2fs_msg(sb, KERN_INFO,
+			"Invalid segment count (%u)",
+			segment_count);
+		return 1;
+	}
+
+	if (total_sections > segment_count ||
+			total_sections < F2FS_MIN_SEGMENTS ||
+			segs_per_sec > segment_count || !segs_per_sec) {
+		f2fs_msg(sb, KERN_INFO,
+			"Invalid segment/section count (%u, %u x %u)",
+			segment_count, total_sections, segs_per_sec);
+		return 1;
+	}
+
+	if ((segment_count / segs_per_sec) < total_sections) {
+		f2fs_msg(sb, KERN_INFO,
+			"Small segment_count (%u < %u * %u)",
+			segment_count, segs_per_sec, total_sections);
+		return 1;
+	}
+
+	if (segment_count > (le32_to_cpu(raw_super->block_count) >> 9)) {
+		f2fs_msg(sb, KERN_INFO,
+			"Wrong segment_count / block_count (%u > %u)",
+			segment_count, le32_to_cpu(raw_super->block_count));
+		return 1;
+	}
+
+	if (secs_per_zone > total_sections) {
+		f2fs_msg(sb, KERN_INFO,
+			"Wrong secs_per_zone (%u > %u)",
+			secs_per_zone, total_sections);
+		return 1;
+	}
+	if (le32_to_cpu(raw_super->extension_count) > F2FS_MAX_EXTENSION ||
+			raw_super->hot_ext_count > F2FS_MAX_EXTENSION ||
+			(le32_to_cpu(raw_super->extension_count) +
+			raw_super->hot_ext_count) > F2FS_MAX_EXTENSION) {
+		f2fs_msg(sb, KERN_INFO,
+			"Corrupted extension count (%u + %u > %u)",
+			le32_to_cpu(raw_super->extension_count),
+			raw_super->hot_ext_count,
+			F2FS_MAX_EXTENSION);
+		return 1;
+	}
+
+	if (le32_to_cpu(raw_super->cp_payload) >
+				(blocks_per_seg - F2FS_CP_PACKS)) {
+		f2fs_msg(sb, KERN_INFO,
+			"Insane cp_payload (%u > %u)",
+			le32_to_cpu(raw_super->cp_payload),
+			blocks_per_seg - F2FS_CP_PACKS);
+		return 1;
+	}
+
 	/* check reserved ino info */
 	if (le32_to_cpu(raw_super->node_ino) != 1 ||
 		le32_to_cpu(raw_super->meta_ino) != 2 ||
@@ -2207,13 +2275,6 @@ static int sanity_check_raw_super(struct f2fs_sb_info *sbi,
 		return 1;
 	}
 
-	if (le32_to_cpu(raw_super->segment_count) > F2FS_MAX_SEGMENT) {
-		f2fs_msg(sb, KERN_INFO,
-			"Invalid segment count (%u)",
-			le32_to_cpu(raw_super->segment_count));
-		return 1;
-	}
-
 	/* check CP/SIT/NAT/SSA/MAIN_AREA area boundary */
 	if (sanity_check_area_boundary(sbi, bh))
 		return 1;