From 13c7fa8c637f62ed32ae8231dc395d76503c6fdf Mon Sep 17 00:00:00 2001 From: Namjae Jeon Date: Sat, 30 Aug 2025 14:44:35 +0900 Subject: [PATCH] exfat: validate cluster allocation bits of the allocation bitmap This patch adds exfat_test_bitmap_range to validate that clusters used for the allocation bitmap are correctly marked as in-use. Signed-off-by: Namjae Jeon --- fs/exfat/balloc.c | 72 +++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 60 insertions(+), 12 deletions(-) diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c index cc01556c9d9b..c09bdb1762f4 100644 --- a/fs/exfat/balloc.c +++ b/fs/exfat/balloc.c @@ -26,12 +26,55 @@ /* * Allocation Bitmap Management Functions */ +static bool exfat_test_bitmap_range(struct super_block *sb, unsigned int clu, + unsigned int count) +{ + struct exfat_sb_info *sbi = EXFAT_SB(sb); + unsigned int start = clu; + unsigned int end = clu + count; + unsigned int ent_idx, i, b; + unsigned int bit_offset, bits_to_check; + __le_long *bitmap_le; + unsigned long mask, word; + + if (!is_valid_cluster(sbi, start) || !is_valid_cluster(sbi, end - 1)) + return -EINVAL; + + while (start < end) { + ent_idx = CLUSTER_TO_BITMAP_ENT(start); + i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx); + b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx); + + bitmap_le = (__le_long *)sbi->vol_amap[i]->b_data; + + /* Calculate how many bits we can check in the current word */ + bit_offset = b % BITS_PER_LONG; + bits_to_check = min(end - start, + (unsigned int)(BITS_PER_LONG - bit_offset)); + + /* Create a bitmask for the range of bits to check */ + if (bits_to_check >= BITS_PER_LONG) + mask = ~0UL; + else + mask = ((1UL << bits_to_check) - 1) << bit_offset; + word = lel_to_cpu(bitmap_le[b / BITS_PER_LONG]); + + /* Check if all bits in the mask are set */ + if ((word & mask) != mask) + return false; + + start += bits_to_check; + } + + return true; +} + static int exfat_allocate_bitmap(struct super_block *sb, struct exfat_dentry *ep) { struct exfat_sb_info *sbi = EXFAT_SB(sb); long long map_size; - unsigned int i, need_map_size; + unsigned int i, j, need_map_size; sector_t sector; sbi->map_clu = le32_to_cpu(ep->dentry.bitmap.start_clu); @@ -58,20 +101,25 @@ static int exfat_allocate_bitmap(struct super_block *sb, sector = exfat_cluster_to_sector(sbi, sbi->map_clu); for (i = 0; i < sbi->map_sectors; i++) { sbi->vol_amap[i] = sb_bread(sb, sector + i); - if (!sbi->vol_amap[i]) { - /* release all buffers and free vol_amap */ - int j = 0; - - while (j < i) - brelse(sbi->vol_amap[j++]); - - kvfree(sbi->vol_amap); - sbi->vol_amap = NULL; - return -EIO; - } + if (!sbi->vol_amap[i]) + goto err_out; } + if (exfat_test_bitmap_range(sb, sbi->map_clu, + round_up(map_size, sbi->cluster_size) >> sbi->cluster_size_bits) == false) + goto err_out; + return 0; + +err_out: + j = 0; + /* release all buffers and free vol_amap */ + while (j < i) + brelse(sbi->vol_amap[j++]); + + kvfree(sbi->vol_amap); + sbi->vol_amap = NULL; + return -EIO; } int exfat_load_bitmap(struct super_block *sb) -- 2.25.1