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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

Reported-by: Wen Xu <wen.xu@gatech.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16: use EIO instead of EFSCORRUPTED]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Theodore Ts'o 2018-03-29 21:56:09 -04:00 committed by syphyr
parent e94a2800cd
commit 159670c416
1 changed files with 6 additions and 0 deletions
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6
fs/ext4/inode.c
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@ -4227,6 +4227,12 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
}
raw_inode = ext4_raw_inode(&iloc);
if ((ino == EXT4_ROOT_INO) && (raw_inode->i_links_count == 0)) {
EXT4_ERROR_INODE(inode, "root inode unallocated");
ret = -EIO;
goto bad_inode;
}
if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >