* RE: [PATCH] fscrypt: don't set policy for a dead directory
2019-05-08 3:55 ` [PATCH] fscrypt: don't set policy for a dead directory Eric Biggers
@ 2019-05-08 4:55 ` Fang Hongjie(方洪杰)
0 siblings, 0 replies; 2+ messages in thread
From: Fang Hongjie(方洪杰) @ 2019-05-08 4:55 UTC (permalink / raw)
To: Eric Biggers
Cc: tytso@mit.edu, jaegeuk@kernel.org, linux-fscrypt@vger.kernel.org,
linux-ext4@vger.kernel.org
> From: Eric Biggers [mailto:ebiggers@kernel.org]
> Sent: Wednesday, May 08, 2019 11:55 AM
> To: Fang Hongjie(方洪杰)
> Cc: tytso@mit.edu; jaegeuk@kernel.org; linux-fscrypt@vger.kernel.org;
> linux-ext4@vger.kernel.org
> Subject: Re: [PATCH] fscrypt: don't set policy for a dead directory
>
> [+Cc linux-ext4]
>
> On Wed, May 08, 2019 at 02:11:10AM +0000, Fang Hongjie(方洪杰) wrote:
> >
> > > -----Original Message-----
> > > From: Eric Biggers [mailto:ebiggers@kernel.org]
> > > Sent: Tuesday, May 07, 2019 11:56 PM
> > > To: Fang Hongjie(方洪杰)
> > > Cc: tytso@mit.edu; jaegeuk@kernel.org; linux-fscrypt@vger.kernel.org
> > > Subject: Re: [PATCH] fscrypt: don't set policy for a dead directory
> > >
> > > Hi,
> > >
> > > On Tue, May 07, 2019 at 12:41:48PM +0800, hongjiefang wrote:
> > > > if the directory had been removed, should not set policy for it.
> > > >
> > > > Signed-off-by: hongjiefang <hongjiefang@asrmicro.com>
> > >
> > > Can you explain the motivation for this change? It makes some sense, but I
> > > don't see why it's really needed. If you look at all the other IS_DEADDIR()
> > > checks in the kernel, they're not for operations on the directory inode itself,
> > > but rather for creating/finding/listing entries in the directory. I think
> > > FS_IOC_SET_ENCRYPTION_POLICY is more like the former (though it does have
> to
> > > check whether the directory is empty).
> >
> > I met a panic issue when run the syzkaller on kernel 4.14.81(EXT4 FBE enabled).
> > the flow of case as follow:
> > r0 = openat$dir(0xffffffffffffff9c, &(0x7f0000000000)='.\x00', 0x0, 0x0)
> > mkdirat(r0, &(0x7f0000000040)='./file0\x00', 0x0)
> > r1 = openat$dir(0xffffffffffffff9c, &(0x7f0000000140)='./file0\x00', 0x0, 0x0)
> > unlinkat(r0, &(0x7f0000000240)='./file0\x00', 0x200)
> > ioctl$FS_IOC_SET_ENCRYPTION_POLICY(r1, 0x800c6613, &(0x7f00000000c0)
> > ={0x0, @aes128, 0x0, "8acc73da97d6accc"})
> >
> > The file0 directory maybe removed before doing
> FS_IOC_SET_ENCRYPTION_POLICY.
> > In this case, fscrypt_ioctl_set_policy()-> ext4_empty_dir() will return the
> > " invalid size " and trigger a panic when check the i_size of inode.
> > the panic stack as follow:
> > PID: 2682 TASK: ffffffc087d18080 CPU: 3 COMMAND: "syz-executor"
> > #0 [ffffffc087d26fc0] panic at ffffff90080dc04c
> > #1 [ffffffc087d27260] ext4_handle_error at ffffff9008689b08
> > #2 [ffffffc087d27290] __ext4_error_inode at ffffff9008689e90
> > #3 [ffffffc087d273f0] ext4_empty_dir at ffffff900865b064
> > #4 [ffffffc087d274d0] fscrypt_ioctl_set_policy at ffffff9008565d70
> > #5 [ffffffc087d27630] ext4_ioctl at ffffff900863105c
> > #6 [ffffffc087d27b00] do_vfs_ioctl at ffffff90084cc440
> > #7 [ffffffc087d27e80] sys_ioctl at ffffff90084cdaf0
> > #8 [ffffffc087d27ff0] el0_svc_naked at ffffff9008084ffc
> >
> > So, it need to check the directory status in the fscrypt_ioctl_set_policy().
> >
>
> Okay, this is a real bug, thanks for reporting this! So ext4_rmdir() sets
> i_size = 0, then ext4_empty_dir() reports an error because 'inode->i_size <
> EXT4_DIR_REC_LEN(1) + EXT4_DIR_REC_LEN(2)'. Note that it's actually an ext4
> error, not necessarily a panic. But the fs may be mounted with errors=panic.
>
> This could also be fixed by updating ext4_empty_dir() to allow i_size == 0. But
> we might as well check IS_DEADDIR() in fscrypt_ioctl_set_policy() either way.
>
> Can you please update the commit message to describe the problem, and add:
>
> Fixes: 9bd8212f981e ("ext4 crypto: add encryption policy and password salt
> support")
> Cc: <stable@vger.kernel.org> # v4.1+
>
Okay，I will update it.
> (Another comment below)
>
> >
> > >
> > > > ---
> > > > fs/crypto/policy.c | 7 +++++++
> > > > 1 file changed, 7 insertions(+)
> > > >
> > > > diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
> > > > index bd7eaf9..82900a4 100644
> > > > --- a/fs/crypto/policy.c
> > > > +++ b/fs/crypto/policy.c
> > > > @@ -77,6 +77,12 @@ int fscrypt_ioctl_set_policy(struct file *filp, const void
> __user
> > > *arg)
> > > >
> > > > inode_lock(inode);
> > > >
> > > > + /* don't set policy for a dead directory */
> > > > + if (IS_DEADDIR(inode)) {
> > > > + ret = -ENOENT;
> > > > + goto deaddir_out;
> > > > + }
> > > > +
>
> This seems a bit misplaced given the actual purpose of the check, and the
> comment doesn't help explain it. How about moving this to just before the
> ->empty_dir() call, so it's only done when actually setting a new policy?
> I think that would make it more obvious:
>
> diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
> index d536889ac31bf..4941fe8471cef 100644
> --- a/fs/crypto/policy.c
> +++ b/fs/crypto/policy.c
> @@ -81,6 +81,8 @@ int fscrypt_ioctl_set_policy(struct file *filp, const void __user
> *arg)
> if (ret == -ENODATA) {
> if (!S_ISDIR(inode->i_mode))
> ret = -ENOTDIR;
> + else if (IS_DEADDIR(inode))
> + ret = -ENOENT;
> else if (!inode->i_sb->s_cop->empty_dir(inode))
> ret = -ENOTEMPTY;
> else
>
> (Then the label below wouldn't be needed, of course.)
>
Yeah, this is a more appropriate way.
Thanks for the comment.
> > > > ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
> > > > if (ret == -ENODATA) {
> > > > if (!S_ISDIR(inode->i_mode))
> > > > @@ -96,6 +102,7 @@ int fscrypt_ioctl_set_policy(struct file *filp, const void
> __user
> > > *arg)
> > > > ret = -EEXIST;
> > > > }
> > > >
> > > > +deaddir_out:
> > > > inode_unlock(inode);
> > >
> > > Call this label 'out_unlock' instead?
> > >
> > > >
> > > > mnt_drop_write_file(filp);
> > > > --
>
> Thanks,
>
> - Eric
B&R
Hongjie
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