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

Ondřej Jirman
2020-03-22T12:14:37Z

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

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
>