Following process:
Init: v2_read_file_info: <3> dqi_free_blk 0 dqi_free_entry 5 dqi_blks 6
Step 1. chown bin f_a -> dquot_acquire -> v2_write_dquot:
qtree_write_dquot
do_insert_tree
find_free_dqentry
get_free_dqblk
write_blk(info->dqi_blocks) // info->dqi_blocks = 6, failure. The
content in physical block (corresponding to blk 6) is random.
Step 2. chown root f_a -> dquot_transfer -> dqput_all -> dqput ->
ext4_release_dquot -> v2_release_dquot -> qtree_delete_dquot:
dquot_release
remove_tree
free_dqentry
put_free_dqblk(6)
info->dqi_free_blk = blk // info->dqi_free_blk = 6
Step 3. drop cache (buffer head for block 6 is released)
Step 4. chown bin f_b -> dquot_acquire -> commit_dqblk -> v2_write_dquot:
qtree_write_dquot
do_insert_tree
find_free_dqentry
get_free_dqblk
dh = (struct qt_disk_dqdbheader *)buf
blk = info->dqi_free_blk // 6
ret = read_blk(info, blk, buf) // The content of buf is random
info->dqi_free_blk = le32_to_cpu(dh->dqdh_next_free) // random blk
Step 5. chown bin f_c -> notify_change -> ext4_setattr -> dquot_transfer:
dquot = dqget -> acquire_dquot -> ext4_acquire_dquot -> dquot_acquire ->
commit_dqblk -> v2_write_dquot -> dq_insert_tree:
do_insert_tree
find_free_dqentry
get_free_dqblk
blk = info->dqi_free_blk // If blk < 0 and blk is not an error
code, it will be returned as dquot
transfer_to[USRQUOTA] = dquot // A random negative value
__dquot_transfer(transfer_to)
dquot_add_inodes(transfer_to[cnt])
spin_lock(&dquot->dq_dqb_lock) // page fault
, which will lead to kernel page fault:
Quota error (device sda): qtree_write_dquot: Error -8000 occurred
while creating quota
BUG: unable to handle page fault for address: ffffffffffffe120
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
Oops: 0002 [#1] PREEMPT SMP
CPU: 0 PID: 5974 Comm: chown Not tainted 6.0.0-rc1-00004
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
RIP: 0010:_raw_spin_lock+0x3a/0x90
Call Trace:
dquot_add_inodes+0x28/0x270
__dquot_transfer+0x377/0x840
dquot_transfer+0xde/0x540
ext4_setattr+0x405/0x14d0
notify_change+0x68e/0x9f0
chown_common+0x300/0x430
__x64_sys_fchownat+0x29/0x40
In order to avoid accessing invalid quota memory address, this patch adds
block number checking of next/prev free block read from quota file.
Fetch a reproducer in [Link].
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216372
Fixes: 1da177e4c3f4152 ("Linux-2.6.12-rc2")
Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
---
fs/quota/quota_tree.c | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)
diff --git a/fs/quota/quota_tree.c b/fs/quota/quota_tree.c
index 5f2405994280..f2e7f5b869a4 100644
--- a/fs/quota/quota_tree.c
+++ b/fs/quota/quota_tree.c
@@ -71,6 +71,35 @@ static ssize_t write_blk(struct qtree_mem_dqinfo *info, uint blk, char *buf)
return ret;
}
+static inline int do_check_range(struct super_block *sb, uint val, uint max_val)
+{
+ if (val >= max_val) {
+ quota_error(sb, "Getting block too big (%u >= %u)",
+ val, max_val);
+ return -EUCLEAN;
+ }
+
+ return 0;
+}
+
+static int check_free_block(struct qtree_mem_dqinfo *info,
+ struct qt_disk_dqdbheader *dh)
+{
+ int err = 0;
+ uint nextblk, prevblk;
+
+ nextblk = le32_to_cpu(dh->dqdh_next_free);
+ err = do_check_range(info->dqi_sb, nextblk, info->dqi_blocks);
+ if (err)
+ return err;
+ prevblk = le32_to_cpu(dh->dqdh_prev_free);
+ err = do_check_range(info->dqi_sb, prevblk, info->dqi_blocks);
+ if (err)
+ return err;
+
+ return err;
+}
+
/* Remove empty block from list and return it */
static int get_free_dqblk(struct qtree_mem_dqinfo *info)
{
@@ -85,6 +114,9 @@ static int get_free_dqblk(struct qtree_mem_dqinfo *info)
ret = read_blk(info, blk, buf);
if (ret < 0)
goto out_buf;
+ ret = check_free_block(info, dh);
+ if (ret)
+ goto out_buf;
info->dqi_free_blk = le32_to_cpu(dh->dqdh_next_free);
}
else {
@@ -232,6 +264,9 @@ static uint find_free_dqentry(struct qtree_mem_dqinfo *info,
*err = read_blk(info, blk, buf);
if (*err < 0)
goto out_buf;
+ *err = check_free_block(info, dh);
+ if (*err)
+ goto out_buf;
} else {
blk = get_free_dqblk(info);
if ((int)blk < 0) {
@@ -424,6 +459,9 @@ static int free_dqentry(struct qtree_mem_dqinfo *info, struct dquot *dquot,
goto out_buf;
}
dh = (struct qt_disk_dqdbheader *)buf;
+ ret = check_free_block(info, dh);
+ if (ret)
+ goto out_buf;
le16_add_cpu(&dh->dqdh_entries, -1);
if (!le16_to_cpu(dh->dqdh_entries)) { /* Block got free? */
ret = remove_free_dqentry(info, buf, blk);
--
2.31.1
