Re: [PATCH] f2fs: allocate buffer for decrypting filename to avoid panic

[Yunlong Song <yunlong.song@huawei.com>]

Hi, Eric,
     Thanks for your review, I have removed the symlink part and use
kmemdup instead. As for directory pages restricted to lowmem, I am
not sure whether it is proper for f2fs, since the directory structures
of f2fs are different from ext4. So I just keep its old kmap.

On 2018/2/25 2:32, Eric Biggers wrote:
> Hi Yunlong,
> 
> On Sat, Feb 24, 2018 at 05:14:58PM +0800, Yunlong Song wrote:
>> In some platforms (such as arm), high memory is used, then the
>> decrypting filename will cause panic, the reason see commit
>> 569cf1876a32e574ba8a7fb825cd91bafd003882 ("f2fs crypto: allocate buffer
>> for decrypting filename"):
>>
>>   We got dentry pages from high_mem, and its address space directly goes into the
>>   decryption path via f2fs_fname_disk_to_usr.
>>   But, sg_init_one assumes the address is not from high_mem, so we can get this
>>   panic since it doesn't call kmap_high but kunmap_high is triggered at the end.
>>
>>   kernel BUG at ../../../../../../kernel/mm/highmem.c:290!
>>   Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
>>   ...
>>    (kunmap_high+0xb0/0xb8) from [<c0114534>] (__kunmap_atomic+0xa0/0xa4)
>>    (__kunmap_atomic+0xa0/0xa4) from [<c035f028>] (blkcipher_walk_done+0x128/0x1ec)
>>    (blkcipher_walk_done+0x128/0x1ec) from [<c0366c24>] (crypto_cbc_decrypt+0xc0/0x170)
>>    (crypto_cbc_decrypt+0xc0/0x170) from [<c0367148>] (crypto_cts_decrypt+0xc0/0x114)
>>    (crypto_cts_decrypt+0xc0/0x114) from [<c035ea98>] (async_decrypt+0x40/0x48)
>>    (async_decrypt+0x40/0x48) from [<c032ca34>] (f2fs_fname_disk_to_usr+0x124/0x304)
>>    (f2fs_fname_disk_to_usr+0x124/0x304) from [<c03056fc>] (f2fs_fill_dentries+0xac/0x188)
>>    (f2fs_fill_dentries+0xac/0x188) from [<c03059c8>] (f2fs_readdir+0x1f0/0x300)
>>    (f2fs_readdir+0x1f0/0x300) from [<c0218054>] (vfs_readdir+0x90/0xb4)
>>    (vfs_readdir+0x90/0xb4) from [<c0218418>] (SyS_getdents64+0x64/0xcc)
>>    (SyS_getdents64+0x64/0xcc) from [<c0105ba0>] (ret_fast_syscall+0x0/0x30)
>>
>> Howerver, later patches:
>> commit 922ec355f86365388203672119b5bca346a45085 ("f2fs crypto: avoid
>> unneeded memory allocation when {en/de}crypting symlink")
>> commit e06f86e61d7a67fe6e826010f57aa39c674f4b1b ("f2fs crypto: avoid
>> unneeded memory allocation in ->readdir")
>>
>> reverts the codes, which causes panic again in arm, so let's add the old
>> patch again.
>>
>> Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
>> ---
>>   fs/f2fs/dir.c   |  7 +++++++
>>   fs/f2fs/namei.c | 10 +++++++++-
>>   2 files changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
>> index f00b5ed..c0cf3e7b 100644
>> --- a/fs/f2fs/dir.c
>> +++ b/fs/f2fs/dir.c
>> @@ -825,9 +825,16 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
>>   			int save_len = fstr->len;
>>   			int err;
>>   
>> +			de_name.name = kmalloc(de_name.len, GFP_NOFS);
>> +			if (!de_name.name)
>> +				return -ENOMEM;
>> +
>> +			memcpy(de_name.name, d->filename[bit_pos], de_name.len);
>> +
>>   			err = fscrypt_fname_disk_to_usr(d->inode,
>>   						(u32)de->hash_code, 0,
>>   						&de_name, fstr);
>> +			kfree(de_name.name);
>>   			if (err)
>>   				return err;
>>   
>> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
>> index c4c94c7..2cb70c1 100644
>> --- a/fs/f2fs/namei.c
>> +++ b/fs/f2fs/namei.c
>> @@ -1170,8 +1170,13 @@ static const char *f2fs_encrypted_get_link(struct dentry *dentry,
>>   
>>   	/* Symlink is encrypted */
>>   	sd = (struct fscrypt_symlink_data *)caddr;
>> -	cstr.name = sd->encrypted_path;
>>   	cstr.len = le16_to_cpu(sd->len);
>> +	cstr.name = kmalloc(cstr.len, GFP_NOFS);
>> +	if (!cstr.name) {
>> +		res = -ENOMEM;
>> +		goto errout;
>> +	}
>> +	memcpy(cstr.name, sd->encrypted_path, cstr.len);
>>   
>>   	/* this is broken symlink case */
>>   	if (unlikely(cstr.len == 0)) {
>> @@ -1198,6 +1203,8 @@ static const char *f2fs_encrypted_get_link(struct dentry *dentry,
>>   		goto errout;
>>   	}
>>   
>> +	kfree(cstr.name);
>> +
>>   	paddr = pstr.name;
>>   
>>   	/* Null-terminate the name */
>> @@ -1207,6 +1214,7 @@ static const char *f2fs_encrypted_get_link(struct dentry *dentry,
>>   	set_delayed_call(done, kfree_link, paddr);
>>   	return paddr;
>>   errout:
>> +	kfree(cstr.name);
>>   	fscrypt_fname_free_buffer(&pstr);
>>   	put_page(cpage);
>>   	return ERR_PTR(res);
>> -- 
>> 1.8.5.2
>>
> 
> The pagecache for symlinks in f2fs already uses lowmem only, so the change to
> ->get_link() isn't needed.  Also that part of the patch doesn't apply to
> upstream.
> 
> For directories we may need your fix.  Note: kmalloc + memcpy should be replaced
> with kmemdup.  But alternatively, directory pages could be restricted to lowmem
> which would match ext4.
> 
> Eric
> 
> .
> 

-- 
Thanks,
Yunlong Song