ext4: fail ext4_iget for root directory if unallocated
commit 8e4b5eae5decd9dfe5a4ee369c22028f90ab4c44 upstream. If the root directory has an i_links_count of zero, then when the file system is mounted, then when ext4_fill_super() notices the problem and tries to call iput() the root directory in the error return path, ext4_evict_inode() will try to free the inode on disk, before all of the file system structures are set up, and this will result in an OOPS caused by a NULL pointer dereference. This issue has been assigned CVE-2018-1092. https://bugzilla.kernel.org/show_bug.cgi?id=199179 https://bugzilla.redhat.com/show_bug.cgi?id=1560777 Change-Id: I6f9180af19ceaaee76b86c27497385d94531954b Reported-by: Wen Xu <wen.xu@gatech.edu> Signed-off-by: Theodore Ts'o <tytso@mit.edu> [bwh: Backported to 3.2: - Use EIO instead of EFSCORRUPTED - Adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
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@ -3738,6 +3738,13 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
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goto bad_inode;
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}
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raw_inode = ext4_raw_inode(&iloc);
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if ((ino == EXT4_ROOT_INO) && (raw_inode->i_links_count == 0)) {
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EXT4_ERROR_INODE(inode, "root inode unallocated");
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ret = -EIO;
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goto bad_inode;
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}
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inode->i_mode = le16_to_cpu(raw_inode->i_mode);
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inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
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inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
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