linux-kernel - [PATCH v3] f2fs: allocate buffer for decrypting filename to avoid panic

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Date:   Wed, 28 Feb 2018 10:19:40 +0800
From:   Yunlong Song <yunlong.song@...wei.com>
To:     <jaegeuk@...nel.org>, <chao@...nel.org>, <yuchao0@...wei.com>,
        <yunlong.song@...oud.com>, <yunlong.song@...wei.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: [PATCH v3] f2fs: allocate buffer for decrypting filename to avoid panic

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 | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index f00b5ed..de2e295 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 = f2fs_kmalloc(sbi, 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;
 
-- 
1.8.5.2