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

Baokun Li <libaokun1@xxxxxxxxxx> · Sat, 17 Feb 2024 15:41:43 +0800

On 2024/2/14 0:58, Jan Kara wrote:
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@xxxxxxxxxxxxxxx
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
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.
Yes, we could put the next patch before this one, but using
s_mb_group_prealloc as an example makes it easier to understand
why the attr_pointer_pi case is added here.There are several other
variables that don't have more convincing examples.

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
I think it's enough here to make sure that mb_best_avail_max_trim_order
is a positive number, since we always make sure that min_order
is not less than 0, as follows:

         order = fls(ac->ac_g_ex.fe_len) - 1;
         min_order = order - sbi->s_mb_best_avail_max_trim_order;
         if (min_order < 0)
                 min_order = 0;

An oversized mb_best_avail_max_trim_order can be interpreted as
always being CR_ANY_FREE. 😄
---
  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



Thanks!
--
With Best Regards,
Baokun Li
.







