Re: [PATCH] f2fs: fix potential .flags overflow on 32bit architecture

Chao Yu
2020-03-23T01:15:45Z

On 2020/3/22 23:30, Ondřej Jirman wrote:
> On Sun, Mar 22, 2020 at 09:18:56PM +0800, Chao Yu wrote:
>> Hi,
>>
>> On 2020-3-22 20:14, Ondřej Jirman wrote:
>>> Hello,
>>>
>>> On Sun, Mar 22, 2020 at 06:13:27PM +0800, Chao Yu wrote:
>>>> From: Chao Yu <yuchao0@huawei.com>
>>>>
>>>> f2fs_inode_info.flags is unsigned long variable, it has 32 bits
>>>> in 32bit architecture, since we introduced FI_MMAP_FILE flag
>>>> when we support data compression, we may access memory cross
>>>> the border of .flags field, corrupting .i_sem field, result in
>>>> below deadlock.
>>>>
>>>> To fix this issue, let's introduce .extra_flags to grab extra
>>>> space to store those new flags.
>>>>
>>>> Call Trace:
>>>> __schedule+0x8d0/0x13fc
>>>> ? mark_held_locks+0xac/0x100
>>>> schedule+0xcc/0x260
>>>> rwsem_down_write_slowpath+0x3ab/0x65d
>>>> down_write+0xc7/0xe0
>>>> f2fs_drop_nlink+0x3d/0x600 [f2fs]
>>>> f2fs_delete_inline_entry+0x300/0x440 [f2fs]
>>>> f2fs_delete_entry+0x3a1/0x7f0 [f2fs]
>>>> f2fs_unlink+0x500/0x790 [f2fs]
>>>> vfs_unlink+0x211/0x490
>>>> do_unlinkat+0x483/0x520
>>>> sys_unlink+0x4a/0x70
>>>> do_fast_syscall_32+0x12b/0x683
>>>> entry_SYSENTER_32+0xaa/0x102
>>>>
>>>> Fixes: 4c8ff7095bef ("f2fs: support data compression")
>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>> ---
>>>> fs/f2fs/f2fs.h | 26 ++++++++++++++++++++------
>>>> fs/f2fs/inode.c | 1 +
>>>> 2 files changed, 21 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index fcafa68212eb..fcd22df2e9ca 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -695,6 +695,7 @@ struct f2fs_inode_info {
>>>>
>>>> /* Use below internally in f2fs*/
>>>> unsigned long flags; /* use to pass per-file flags */
>>>> + unsigned long extra_flags; /* extra flags */
>>>> struct rw_semaphore i_sem; /* protect fi info */
>>>> atomic_t dirty_pages; /* # of dirty pages */
>>>> f2fs_hash_t chash; /* hash value of given file name */
>>>> @@ -2569,7 +2570,7 @@ enum {
>>>> };
>>>>
>>>> static inline void __mark_inode_dirty_flag(struct inode *inode,
>>>> - int flag, bool set)
>>>> + unsigned long long flag, bool set)
>>>> {
>>>> switch (flag) {
>>>> case FI_INLINE_XATTR:
>>>> @@ -2588,20 +2589,33 @@ static inline void __mark_inode_dirty_flag(struct inode *inode,
>>>>
>>>> static inline void set_inode_flag(struct inode *inode, int flag)
>>>> {
>>>> - if (!test_bit(flag, &F2FS_I(inode)->flags))
>>>> - set_bit(flag, &F2FS_I(inode)->flags);
>>>> + if ((1 << flag) <= sizeof(unsigned long)) {
>>>
>>> ^ this is wrong. Maybe you meant flag <= BITS_PER_LONG
>>
>> Oh, my bad, I meant that, thanks for pointing out this. :)
>>
>>>
>>> And ditto for the same checks below. Maybe you can make flags an array of
>>> BIT_WORD(max_flag_value) + 1 and skip the branches altogether?
>
> I've found maybe a clearer macro for this:
>
> https://elixir.bootlin.com/linux/latest/source/include/linux/bitops.h#L15
>
> BITS_TO_LONGS(nr)

More clean, thanks, will send v3 soon.

Thanks,

>
> But it takes the number of bits in the bitmap, which would be
> "max_flag_value + 1".
>
> regards,
> o.
>
>> That will be better, let me revise this patch.
>>
>> Thanks,
>>
>>>
>>> thank you and regards,
>>> o.
>>>
>>>> + if (!test_bit(flag, &F2FS_I(inode)->flags))
>>>> + set_bit(flag, &F2FS_I(inode)->flags);
>>>> + } else {
>>>> + if (!test_bit(flag - 32, &F2FS_I(inode)->extra_flags))
>>>> + set_bit(flag - 32, &F2FS_I(inode)->extra_flags);
>>>> + }
>>>> __mark_inode_dirty_flag(inode, flag, true);
>>>> }
>>>>
>>>> static inline int is_inode_flag_set(struct inode *inode, int flag)
>>>> {
>>>> - return test_bit(flag, &F2FS_I(inode)->flags);
>>>> + if ((1 << flag) <= sizeof(unsigned long))
>>>> + return test_bit(flag, &F2FS_I(inode)->flags);
>>>> + else
>>>> + return test_bit(flag - 32, &F2FS_I(inode)->extra_flags);
>>>> }
>>>>
>>>> static inline void clear_inode_flag(struct inode *inode, int flag)
>>>> {
>>>> - if (test_bit(flag, &F2FS_I(inode)->flags))
>>>> - clear_bit(flag, &F2FS_I(inode)->flags);
>>>> + if ((1 << flag) <= sizeof(unsigned long)) {
>>>> + if (test_bit(flag, &F2FS_I(inode)->flags))
>>>> + clear_bit(flag, &F2FS_I(inode)->flags);
>>>> + } else {
>>>> + if (test_bit(flag - 32, &F2FS_I(inode)->extra_flags))
>>>> + clear_bit(flag - 32, &F2FS_I(inode)->extra_flags);
>>>> + }
>>>> __mark_inode_dirty_flag(inode, flag, false);
>>>> }
>>>>
>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>>>> index 44e08bf2e2b4..ca924d7e0e30 100644
>>>> --- a/fs/f2fs/inode.c
>>>> +++ b/fs/f2fs/inode.c
>>>> @@ -363,6 +363,7 @@ static int do_read_inode(struct inode *inode)
>>>> if (S_ISREG(inode->i_mode))
>>>> fi->i_flags &= ~F2FS_PROJINHERIT_FL;
>>>> fi->flags = 0;
>>>> + fi->extra_flags = 0;
>>>> fi->i_advise = ri->i_advise;
>>>> fi->i_pino = le32_to_cpu(ri->i_pino);
>>>> fi->i_dir_level = ri->i_dir_level;
>>>> --
>>>> 2.22.0
>>>>
> .
>