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    SubjectRe: [PATCH v2] f2fs: allocate buffer for decrypting filename to avoid panic
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    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@huawei.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;
    >
    >

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