[CVE-2018-1092][T/X/A/B/C] ext4: fail ext4_iget for root directory if unallocated

[CVE-2018-1092][T/X/A/B/C] ext4: fail ext4_iget for root directory if unallocated

[Khalid Elmously]

From: Theodore Ts'o <tytso@mit.edu>

CVE-2018-1092

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>
Cc: stable@vger.kernel.org
(cherry-picked from 8e4b5eae5decd9dfe5a4ee369c22028f90ab4c44)
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
---
 fs/ext4/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 3d4d1dccc8a1..398faeff1938 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4745,6 +4745,12 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 		goto bad_inode;
 	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 = -EFSCORRUPTED;
+		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 >
-- 
2.17.0

Re: [CVE-2018-1092][T/X/A/B/C] ext4: fail ext4_iget for root directory if unallocated

[Greg KH]

On Mon, May 14, 2018 at 01:27:13AM -0400, Khalid Elmously wrote:
> From: Theodore Ts'o <tytso@mit.edu>
> 
> CVE-2018-1092
> 
> 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>
> Cc: stable@vger.kernel.org
> (cherry-picked from 8e4b5eae5decd9dfe5a4ee369c22028f90ab4c44)
> Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
> ---
>  fs/ext4/inode.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Any specific reason you sent a patch that is already included in all of
the active stable trees, to the stable mailing list?

And nice fuzzymail address :)

greg k-h

Re: [CVE-2018-1092][T/X/A/B/C] ext4: fail ext4_iget for root directory if unallocated

[Khalid Elmously]

On 2018-05-14 08:17:52 , Greg KH wrote:
> On Mon, May 14, 2018 at 01:27:13AM -0400, Khalid Elmously wrote:
> > From: Theodore Ts'o <tytso@mit.edu>
> > 
> > CVE-2018-1092
> > 
> > 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>
> > Cc: stable@vger.kernel.org
> > (cherry-picked from 8e4b5eae5decd9dfe5a4ee369c22028f90ab4c44)
> > Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
> > ---
> >  fs/ext4/inode.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> 
> Any specific reason you sent a patch that is already included in all of
> the active stable trees, to the stable mailing list?

Well I thought why not apply the patch again for _extra_ protection?

> 
> And nice fuzzymail address :)

Thanks :)



Seriously though: I mis-used git-send-email while sending a test patch to myself and ended up CC'ing the stable ML - apologies for the spam.

> 
> greg k-h

Khalid