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

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Date:   Sun, 22 Mar 2020 13:14:34 +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

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

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?

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
>