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

Baokun Li
2024-01-26T08:54:50Z

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>
---
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