linux-kernel - Re: [PATCH v2] f2fs: allocate buffer for decrypting filename to avoid panic

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Date:   Tue, 27 Feb 2018 18:40:39 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Yunlong Song <yunlong.song@...wei.com>, <jaegeuk@...nel.org>,
        <chao@...nel.org>, <yunlong.song@...oud.com>
CC:     <miaoxie@...wei.com>, <bintian.wang@...wei.com>,
        <shengyong1@...wei.com>, <heyunlei@...wei.com>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] f2fs: allocate buffer for decrypting filename to avoid
 panic

On 2018/2/26 10:57, 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 e06f86e61d7a67fe6e826010f57aa39c674f4b1b ("f2fs crypto: avoid
> unneeded memory allocation in ->readdir")
> 
> reverts the codes, which causes panic again in arm, so let's add part of
> the old patch again for dentry page.
> 
> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
> ---
>  fs/f2fs/dir.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index f00b5ed..23fff48 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -825,9 +825,15 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
>  			int save_len = fstr->len;
>  			int err;
>  
> +			de_name.name = kmemdup(d->filename[bit_pos],

How about using f2fs_kmalloc + memcpy here?

Thanks,

> +				de_name.len, GFP_NOFS);
> +			if (!de_name.name)
> +				return -ENOMEM;
> +
>  			err = fscrypt_fname_disk_to_usr(d->inode,
>  						(u32)de->hash_code, 0,
>  						&de_name, fstr);
> +			kfree(de_name.name);
>  			if (err)
>  				return err;
>  
>