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

Chao Yu
2020-03-22T13:19:04Z

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?

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
>>