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

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Date:   Sun, 22 Mar 2020 16:30:14 +0100
From:   Ondřej Jirman <megi@....cz>
To:     Chao Yu <chao@...nel.org>
Cc:     jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH] f2fs: fix potential .flags overflow on 32bit architecture

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@...wei.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@...wei.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)

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
> > >