[PATCH] ntfs: Ensure $Extend is a directory

[PATCH] ntfs: Ensure $Extend is a directory

[Soumya Negi]

Fixes Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71

Check whether $Extend is a directory or not( for NTFS3.0+) while loading
system files. If it isn't(as in the case of this bug where the mft record for
$Extend contains a regular file), load_system_files() returns false.

Reported-by: syzbot+30b7f850c6d98ea461d2@syzkaller.appspotmail.com
Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>
---
 fs/ntfs/super.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
index 5ae8de09b271..18e2902531f9 100644
--- a/fs/ntfs/super.c
+++ b/fs/ntfs/super.c
@@ -2092,10 +2092,15 @@ static bool load_system_files(ntfs_volume *vol)
 	// TODO: Initialize security.
 	/* Get the extended system files' directory inode. */
 	vol->extend_ino = ntfs_iget(sb, FILE_Extend);
-	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino)) {
+	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino) ||
+	    !S_ISDIR(vol->extend_ino->i_mode)) {
+		static const char *es1 = "$Extend is not a directory";
+		static const char *es2 = "Failed to load $Extend";
+		const char *es = !S_ISDIR(vol->extend_ino->i_mode) ? es1 : es2;
+
 		if (!IS_ERR(vol->extend_ino))
 			iput(vol->extend_ino);
-		ntfs_error(sb, "Failed to load $Extend.");
+		ntfs_error(sb, "%s.", es);
 		goto iput_sec_err_out;
 	}
 #ifdef NTFS_RW
-- 
2.17.1

Re: [PATCH] ntfs: Ensure $Extend is a directory

[Greg KH]

On Sun, Jul 24, 2022 at 06:21:07AM -0700, Soumya Negi wrote:
> Fixes Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
> https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71
> 
> Check whether $Extend is a directory or not( for NTFS3.0+) while loading
> system files. If it isn't(as in the case of this bug where the mft record for
> $Extend contains a regular file), load_system_files() returns false.

Please wrap your changelog text at 72 columns like your editor asked you
to when writing this :)

> 
> Reported-by: syzbot+30b7f850c6d98ea461d2@syzkaller.appspotmail.com
> Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>

What commit caused this problem?  What Fixes: tag should go here?
Should it go to stable kernels?  If so, how far back?

> ---
>  fs/ntfs/super.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
> index 5ae8de09b271..18e2902531f9 100644
> --- a/fs/ntfs/super.c
> +++ b/fs/ntfs/super.c
> @@ -2092,10 +2092,15 @@ static bool load_system_files(ntfs_volume *vol)
>  	// TODO: Initialize security.
>  	/* Get the extended system files' directory inode. */
>  	vol->extend_ino = ntfs_iget(sb, FILE_Extend);
> -	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino)) {
> +	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino) ||
> +	    !S_ISDIR(vol->extend_ino->i_mode)) {
> +		static const char *es1 = "$Extend is not a directory";
> +		static const char *es2 = "Failed to load $Extend";
> +		const char *es = !S_ISDIR(vol->extend_ino->i_mode) ? es1 : es2;
> +
>  		if (!IS_ERR(vol->extend_ino))
>  			iput(vol->extend_ino);
> -		ntfs_error(sb, "Failed to load $Extend.");
> +		ntfs_error(sb, "%s.", es);

Are you allowing the system log to be spammed by an untrusted user with
this change?

thanks,

greg k-h

Re: [PATCH] ntfs: Ensure $Extend is a directory

[Soumya Negi]

On Sun, Jul 24, 2022 at 03:47:01PM +0200, Greg KH wrote:
> On Sun, Jul 24, 2022 at 06:21:07AM -0700, Soumya Negi wrote:
> > Fixes Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
> > https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71
> > 
> > Check whether $Extend is a directory or not( for NTFS3.0+) while loading
> > system files. If it isn't(as in the case of this bug where the mft record for
> > $Extend contains a regular file), load_system_files() returns false.
> 
> Please wrap your changelog text at 72 columns like your editor asked you
> to when writing this :)

I will correct the changelog(Don't think I can wrap the bug report
link. Checkpatch will still give a warning. Is that okay?).
 
> > Reported-by: syzbot+30b7f850c6d98ea461d2@syzkaller.appspotmail.com
> > Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>
> 
> What commit caused this problem?  What Fixes: tag should go here?

I don't think this was caused by any specific commit.The $Extend
directory check is not present in any previous releases. Syzbot has
also not been able to produce a cause bisection for the bug. So no fixes
tag(please correct me if I am wrong).

> Should it go to stable kernels?  If so, how far back?

Since the NTFS extension file was new to NTFS 3.0, perhaps the patch 
should apply all the way back to the first release with NTFS3.0 support?
I checked the stable tree history and 2.6.11 is the oldest release I could find.

> > ---
> >  fs/ntfs/super.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
> > index 5ae8de09b271..18e2902531f9 100644
> > --- a/fs/ntfs/super.c
> > +++ b/fs/ntfs/super.c
> > @@ -2092,10 +2092,15 @@ static bool load_system_files(ntfs_volume *vol)
> >  	// TODO: Initialize security.
> >  	/* Get the extended system files' directory inode. */
> >  	vol->extend_ino = ntfs_iget(sb, FILE_Extend);
> > -	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino)) {
> > +	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino) ||
> > +	    !S_ISDIR(vol->extend_ino->i_mode)) {
> > +		static const char *es1 = "$Extend is not a directory";
> > +		static const char *es2 = "Failed to load $Extend";
> > +		const char *es = !S_ISDIR(vol->extend_ino->i_mode) ? es1 : es2;
> > +
> >  		if (!IS_ERR(vol->extend_ino))
> >  			iput(vol->extend_ino);
> > -		ntfs_error(sb, "Failed to load $Extend.");
> > +		ntfs_error(sb, "%s.", es);
> 
> Are you allowing the system log to be spammed by an untrusted user with
> this change?

The error message is written to the system log while trying to mount 
the file system(which will fail if the error occurs). I don't understand
how an untrusted user will be involved.

> thanks,
> 
> greg k-h

Thanks,
Soumya

Re: [PATCH] ntfs: Ensure $Extend is a directory

[Greg KH]

On Sun, Jul 24, 2022 at 08:34:48AM -0700, Soumya Negi wrote:
> On Sun, Jul 24, 2022 at 03:47:01PM +0200, Greg KH wrote:
> > On Sun, Jul 24, 2022 at 06:21:07AM -0700, Soumya Negi wrote:
> > > Fixes Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
> > > https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71
> > > 
> > > Check whether $Extend is a directory or not( for NTFS3.0+) while loading
> > > system files. If it isn't(as in the case of this bug where the mft record for
> > > $Extend contains a regular file), load_system_files() returns false.
> > 
> > Please wrap your changelog text at 72 columns like your editor asked you
> > to when writing this :)
> 
> I will correct the changelog(Don't think I can wrap the bug report
> link. Checkpatch will still give a warning. Is that okay?).

Yes, do not wrap links.

> > > Reported-by: syzbot+30b7f850c6d98ea461d2@syzkaller.appspotmail.com
> > > Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>
> > 
> > What commit caused this problem?  What Fixes: tag should go here?
> 
> I don't think this was caused by any specific commit.The $Extend
> directory check is not present in any previous releases. Syzbot has
> also not been able to produce a cause bisection for the bug. So no fixes
> tag(please correct me if I am wrong).
> 
> > Should it go to stable kernels?  If so, how far back?
> 
> Since the NTFS extension file was new to NTFS 3.0, perhaps the patch 
> should apply all the way back to the first release with NTFS3.0 support?

Yes, mark it there.

thanks,

greg k-h

Re: [PATCH] ntfs: Ensure $Extend is a directory

[Soumya Negi]

On Sun, Jul 24, 2022 at 05:54:43PM +0200, Greg KH wrote:
> On Sun, Jul 24, 2022 at 08:34:48AM -0700, Soumya Negi wrote:
> > On Sun, Jul 24, 2022 at 03:47:01PM +0200, Greg KH wrote:
> > > On Sun, Jul 24, 2022 at 06:21:07AM -0700, Soumya Negi wrote:
> > > > Fixes Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
> > > > https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71
> > > > 
> > > > Check whether $Extend is a directory or not( for NTFS3.0+) while loading
> > > > system files. If it isn't(as in the case of this bug where the mft record for
> > > > $Extend contains a regular file), load_system_files() returns false.
> > > 
> > > Please wrap your changelog text at 72 columns like your editor asked you
> > > to when writing this :)
> > 
> > I will correct the changelog(Don't think I can wrap the bug report
> > link. Checkpatch will still give a warning. Is that okay?).
> 
> Yes, do not wrap links.
> 
> > > > Reported-by: syzbot+30b7f850c6d98ea461d2@syzkaller.appspotmail.com
> > > > Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>
> > > 
> > > What commit caused this problem?  What Fixes: tag should go here?
> > 
> > I don't think this was caused by any specific commit.The $Extend
> > directory check is not present in any previous releases. Syzbot has
> > also not been able to produce a cause bisection for the bug. So no fixes
> > tag(please correct me if I am wrong).
> > 
> > > Should it go to stable kernels?  If so, how far back?
> > 
> > Since the NTFS extension file was new to NTFS 3.0, perhaps the patch 
> > should apply all the way back to the first release with NTFS3.0 support?

> Yes, mark it there.

Thanks. I will send v2 of the patch. Just want to make sure that the
patch will apply to 2.6.11.y before marking it.

-Soumya

Re: [PATCH] ntfs: Ensure $Extend is a directory

[Soumya Negi]

Hi,

On Sun, Jul 24, 2022 at 03:17:45PM -0700, Soumya Negi wrote:
> On Sun, Jul 24, 2022 at 05:54:43PM +0200, Greg KH wrote:
> > On Sun, Jul 24, 2022 at 08:34:48AM -0700, Soumya Negi wrote:
> > > On Sun, Jul 24, 2022 at 03:47:01PM +0200, Greg KH wrote:
> > > > On Sun, Jul 24, 2022 at 06:21:07AM -0700, Soumya Negi wrote:
> > > > > Fixes Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
> > > > > https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71
> > > > > 
> > > > > Check whether $Extend is a directory or not( for NTFS3.0+) while loading
> > > > > system files. If it isn't(as in the case of this bug where the mft record for
> > > > > $Extend contains a regular file), load_system_files() returns false.
> > > > 
> > > > Please wrap your changelog text at 72 columns like your editor asked you
> > > > to when writing this :)
> > > 
> > > I will correct the changelog(Don't think I can wrap the bug report
> > > link. Checkpatch will still give a warning. Is that okay?).
> > 
> > Yes, do not wrap links.
> > 
> > > > > Reported-by: syzbot+30b7f850c6d98ea461d2@syzkaller.appspotmail.com
> > > > > Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>
> > > > 
> > > > What commit caused this problem?  What Fixes: tag should go here?
> > > 
> > > I don't think this was caused by any specific commit.The $Extend
> > > directory check is not present in any previous releases. Syzbot has
> > > also not been able to produce a cause bisection for the bug. So no fixes
> > > tag(please correct me if I am wrong).
> > > 
> > > > Should it go to stable kernels?  If so, how far back?
> > > 
> > > Since the NTFS extension file was new to NTFS 3.0, perhaps the patch 
> > > should apply all the way back to the first release with NTFS3.0 support?
> 
> > Yes, mark it there.
> 
> Thanks. I will send v2 of the patch. Just want to make sure that the
> patch will apply to 2.6.11.y before marking it.

2.6.11 is where I think NTFS3.0 support was first present and till where
the patch should go. But I am not able to build 2.6.11 on my system and
test the patch. I tried the patch on 4.14 and it works. Should I mark it
to be backported till 4.14 instead?

With thanks,
Soumya

Re: [PATCH] ntfs: Ensure $Extend is a directory

[Greg KH]

On Mon, Jul 25, 2022 at 12:06:56PM -0700, Soumya Negi wrote:
> Hi,
> 
> On Sun, Jul 24, 2022 at 03:17:45PM -0700, Soumya Negi wrote:
> > On Sun, Jul 24, 2022 at 05:54:43PM +0200, Greg KH wrote:
> > > On Sun, Jul 24, 2022 at 08:34:48AM -0700, Soumya Negi wrote:
> > > > On Sun, Jul 24, 2022 at 03:47:01PM +0200, Greg KH wrote:
> > > > > On Sun, Jul 24, 2022 at 06:21:07AM -0700, Soumya Negi wrote:
> > > > > > Fixes Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
> > > > > > https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71
> > > > > > 
> > > > > > Check whether $Extend is a directory or not( for NTFS3.0+) while loading
> > > > > > system files. If it isn't(as in the case of this bug where the mft record for
> > > > > > $Extend contains a regular file), load_system_files() returns false.
> > > > > 
> > > > > Please wrap your changelog text at 72 columns like your editor asked you
> > > > > to when writing this :)
> > > > 
> > > > I will correct the changelog(Don't think I can wrap the bug report
> > > > link. Checkpatch will still give a warning. Is that okay?).
> > > 
> > > Yes, do not wrap links.
> > > 
> > > > > > Reported-by: syzbot+30b7f850c6d98ea461d2@syzkaller.appspotmail.com
> > > > > > Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>
> > > > > 
> > > > > What commit caused this problem?  What Fixes: tag should go here?
> > > > 
> > > > I don't think this was caused by any specific commit.The $Extend
> > > > directory check is not present in any previous releases. Syzbot has
> > > > also not been able to produce a cause bisection for the bug. So no fixes
> > > > tag(please correct me if I am wrong).
> > > > 
> > > > > Should it go to stable kernels?  If so, how far back?
> > > > 
> > > > Since the NTFS extension file was new to NTFS 3.0, perhaps the patch 
> > > > should apply all the way back to the first release with NTFS3.0 support?
> > 
> > > Yes, mark it there.
> > 
> > Thanks. I will send v2 of the patch. Just want to make sure that the
> > patch will apply to 2.6.11.y before marking it.
> 
> 2.6.11 is where I think NTFS3.0 support was first present and till where
> the patch should go. But I am not able to build 2.6.11 on my system and
> test the patch. I tried the patch on 4.14 and it works. Should I mark it
> to be backported till 4.14 instead?

Say 4.9 and you will get an email saying it failed to apply there when
it gets merged into Linus's tree, and then you can provide a working
patch for us to add to stable.

thanks,

greg k-h