Re: [PATCH 4/7] ext4: add positive int attr pointer to avoid sysfs variables overflow

[Jan Kara <jack@suse.cz>]

On Fri 26-01-24 16:57:13, Baokun Li wrote:
> We can easily trigger a BUG_ON by using the following commands:
> 
>     mount /dev/$disk /tmp/test
>     echo 2147483650 > /sys/fs/ext4/$disk/mb_group_prealloc
>     echo test > /tmp/test/file && sync
> 
> ==================================================================
> kernel BUG at fs/ext4/mballoc.c:2029!
> invalid opcode: 0000 [#1] PREEMPT SMP PTI
> CPU: 3 PID: 320 Comm: kworker/u36:1 Not tainted 6.8.0-rc1 #462
> RIP: 0010:mb_mark_used+0x358/0x370
> [...]
> Call Trace:
>  ext4_mb_use_best_found+0x56/0x140
>  ext4_mb_complex_scan_group+0x196/0x2f0
>  ext4_mb_regular_allocator+0xa92/0xf00
>  ext4_mb_new_blocks+0x302/0xbc0
>  ext4_ext_map_blocks+0x95a/0xef0
>  ext4_map_blocks+0x2b1/0x680
>  ext4_do_writepages+0x733/0xbd0
> [...]
> ==================================================================
> 
> In ext4_mb_normalize_group_request():
>     ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc;
> 
> Here fe_len is of type int, but s_mb_group_prealloc is of type unsigned
> int, so setting s_mb_group_prealloc to 2147483650 overflows fe_len to a
> negative number, which ultimately triggers a BUG_ON() in mb_mark_used().
> 
> Therefore, we add attr_pointer_pi (aka positive int attr pointer) with a
> value range of 0-INT_MAX to avoid the above problem. In addition to the
> mb_group_prealloc sysfs interface, the following interfaces also have uint
> to int conversions that result in overflows, and are also fixed.
> 
>   err_ratelimit_burst
>   msg_ratelimit_burst
>   warning_ratelimit_burst
>   err_ratelimit_interval_ms
>   msg_ratelimit_interval_ms
>   warning_ratelimit_interval_ms
>   mb_best_avail_max_trim_order
> 
> CC: stable@vger.kernel.org
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

I don't think you need to change s_mb_group_prealloc here and then restrict
it even further in the next patch. I'd just leave it alone here.

Also I think that limiting mb_best_avail_max_trim_order to 64 instead of
INT_MAX will make us more resilient to surprises in the future :) But I
don't really insist.

								Honza

> ---
>  fs/ext4/sysfs.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index a5d657fa05cb..6f9f96e00f2f 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -30,6 +30,7 @@ typedef enum {
>  	attr_first_error_time,
>  	attr_last_error_time,
>  	attr_feature,
> +	attr_pointer_pi,
>  	attr_pointer_ui,
>  	attr_pointer_ul,
>  	attr_pointer_u64,
> @@ -178,6 +179,9 @@ static struct ext4_attr ext4_attr_##_name = {			\
>  #define EXT4_RO_ATTR_ES_STRING(_name,_elname,_size)			\
>  	EXT4_ATTR_STRING(_name, 0444, _size, ext4_super_block, _elname)
>  
> +#define EXT4_RW_ATTR_SBI_PI(_name,_elname)      \
> +	EXT4_ATTR_OFFSET(_name, 0644, pointer_pi, ext4_sb_info, _elname)
> +
>  #define EXT4_RW_ATTR_SBI_UI(_name,_elname)	\
>  	EXT4_ATTR_OFFSET(_name, 0644, pointer_ui, ext4_sb_info, _elname)
>  
> @@ -213,17 +217,17 @@ EXT4_RW_ATTR_SBI_UI(mb_max_to_scan, s_mb_max_to_scan);
>  EXT4_RW_ATTR_SBI_UI(mb_min_to_scan, s_mb_min_to_scan);
>  EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
>  EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
> -EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
> +EXT4_RW_ATTR_SBI_PI(mb_group_prealloc, s_mb_group_prealloc);
>  EXT4_RW_ATTR_SBI_UI(mb_max_linear_groups, s_mb_max_linear_groups);
>  EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
>  EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
> -EXT4_RW_ATTR_SBI_UI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
> -EXT4_RW_ATTR_SBI_UI(err_ratelimit_burst, s_err_ratelimit_state.burst);
> -EXT4_RW_ATTR_SBI_UI(warning_ratelimit_interval_ms, s_warning_ratelimit_state.interval);
> -EXT4_RW_ATTR_SBI_UI(warning_ratelimit_burst, s_warning_ratelimit_state.burst);
> -EXT4_RW_ATTR_SBI_UI(msg_ratelimit_interval_ms, s_msg_ratelimit_state.interval);
> -EXT4_RW_ATTR_SBI_UI(msg_ratelimit_burst, s_msg_ratelimit_state.burst);
> -EXT4_RW_ATTR_SBI_UI(mb_best_avail_max_trim_order, s_mb_best_avail_max_trim_order);
> +EXT4_RW_ATTR_SBI_PI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
> +EXT4_RW_ATTR_SBI_PI(err_ratelimit_burst, s_err_ratelimit_state.burst);
> +EXT4_RW_ATTR_SBI_PI(warning_ratelimit_interval_ms, s_warning_ratelimit_state.interval);
> +EXT4_RW_ATTR_SBI_PI(warning_ratelimit_burst, s_warning_ratelimit_state.burst);
> +EXT4_RW_ATTR_SBI_PI(msg_ratelimit_interval_ms, s_msg_ratelimit_state.interval);
> +EXT4_RW_ATTR_SBI_PI(msg_ratelimit_burst, s_msg_ratelimit_state.burst);
> +EXT4_RW_ATTR_SBI_PI(mb_best_avail_max_trim_order, s_mb_best_avail_max_trim_order);
>  #ifdef CONFIG_EXT4_DEBUG
>  EXT4_RW_ATTR_SBI_UL(simulate_fail, s_simulate_fail);
>  #endif
> @@ -376,6 +380,7 @@ static ssize_t ext4_generic_attr_show(struct ext4_attr *a,
>  
>  	switch (a->attr_id) {
>  	case attr_inode_readahead:
> +	case attr_pointer_pi:
>  	case attr_pointer_ui:
>  		if (a->attr_ptr == ptr_ext4_super_block_offset)
>  			return sysfs_emit(buf, "%u\n", le32_to_cpup(ptr));
> @@ -448,6 +453,10 @@ static ssize_t ext4_generic_attr_store(struct ext4_attr *a,
>  		return ret;
>  
>  	switch (a->attr_id) {
> +	case attr_pointer_pi:
> +		if ((int)t < 0)
> +			return -EINVAL;
> +		fallthrough;
>  	case attr_pointer_ui:
>  		if (t != (unsigned int)t)
>  			return -EINVAL;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR