From a3082d526f2d406d4b488e49a508a0062a23314f Mon Sep 17 00:00:00 2001 From: OGAWA Hirofumi Date: Wed, 20 Jan 2016 14:59:38 -0800 Subject: [PATCH] fat: add simple validation for directory inode This detects simple corruption cases of directory, and tries to avoid further damage to user data. And performance impact of this validation should be very low, or not measurable. Signed-off-by: OGAWA Hirofumi Reported-by: Vegard Nossum Tested-by: Vegard Nossum Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/fat/inode.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/fs/fat/inode.c b/fs/fat/inode.c index 3ac9078fde65..08ef5fd0d502 100644 --- a/fs/fat/inode.c +++ b/fs/fat/inode.c @@ -449,6 +449,24 @@ static int fat_calc_dir_size(struct inode *inode) return 0; } +static int fat_validate_dir(struct inode *dir) +{ + struct super_block *sb = dir->i_sb; + + if (dir->i_nlink < 2) { + /* Directory should have "."/".." entries at least. */ + fat_fs_error(sb, "corrupted directory (invalid entries)"); + return -EIO; + } + if (MSDOS_I(dir)->i_start == 0 || + MSDOS_I(dir)->i_start == MSDOS_SB(sb)->root_cluster) { + /* Directory should point valid cluster. */ + fat_fs_error(sb, "corrupted directory (invalid i_start)"); + return -EIO; + } + return 0; +} + /* doesn't deal with root inode */ int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de) { @@ -475,6 +493,10 @@ int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de) MSDOS_I(inode)->mmu_private = inode->i_size; set_nlink(inode, fat_subdirs(inode)); + + error = fat_validate_dir(inode); + if (error < 0) + return error; } else { /* not a directory */ inode->i_generation |= 1; inode->i_mode = fat_make_mode(sbi, de->attr, -- 2.20.1