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loop: don't change loop device under exclusive opener in loop_set_status

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loop_set_status() is allowed to change the loop device while there
are other openers of the device, even exclusive ones.

In this case, it causes a KASAN: slab-out-of-bounds Read in
ext4_search_dir(), since when looking for an entry in an inlined
directory, e_value_offs is changed underneath the filesystem by
loop_set_status().

Fix the problem by forbidding loop_set_status() from modifying the loop
device while there are exclusive openers of the device. This is similar
to the fix in loop_configure() by commit 33ec3e53e7 ("loop: Don't
change loop device under exclusive opener") alongside commit ecbe6bc000
("block: use bd_prepare_to_claim directly in the loop driver").

Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
Tested-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Raphael Pinsonneault-Thibeault
2025-12-17 14:00:40 -05:00
committed by Jens Axboe
parent 69153e8b97
commit 08e136ebd1
1 changed files with 30 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

41
drivers/block/loop.c
View File

@@ -1225,13 +1225,24 @@ static int loop_clr_fd(struct loop_device *lo)
}
static int
loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
loop_set_status(struct loop_device *lo, blk_mode_t mode,
struct block_device *bdev, const struct loop_info64 *info)
{
int err;
bool partscan = false;
bool size_changed = false;
unsigned int memflags;
/*
* If we don't hold exclusive handle for the device, upgrade to it
* here to avoid changing device under exclusive owner.
*/
if (!(mode & BLK_OPEN_EXCL)) {
err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
if (err)
goto out_reread_partitions;
}
err = mutex_lock_killable(&lo->lo_mutex);
if (err)
return err;
@@ -1273,6 +1284,9 @@ out_unfreeze:
}
out_unlock:
mutex_unlock(&lo->lo_mutex);
if (!(mode & BLK_OPEN_EXCL))
bd_abort_claiming(bdev, loop_set_status);
out_reread_partitions:
if (partscan)
loop_reread_partitions(lo);
@@ -1352,7 +1366,9 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
}
static int
loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
struct block_device *bdev,
const struct loop_info __user *arg)
{
struct loop_info info;
struct loop_info64 info64;
@@ -1360,17 +1376,19 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
if (copy_from_user(&info, arg, sizeof (struct loop_info)))
return -EFAULT;
loop_info64_from_old(&info, &info64);
return loop_set_status(lo, &info64);
return loop_set_status(lo, mode, bdev, &info64);
}
static int
loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
loop_set_status64(struct loop_device *lo, blk_mode_t mode,
struct block_device *bdev,
const struct loop_info64 __user *arg)
{
struct loop_info64 info64;
if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
return -EFAULT;
return loop_set_status(lo, &info64);
return loop_set_status(lo, mode, bdev, &info64);
}
static int
@@ -1549,14 +1567,14 @@ static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
case LOOP_SET_STATUS:
err = -EPERM;
if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
err = loop_set_status_old(lo, argp);
err = loop_set_status_old(lo, mode, bdev, argp);
break;
case LOOP_GET_STATUS:
return loop_get_status_old(lo, argp);
case LOOP_SET_STATUS64:
err = -EPERM;
if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
err = loop_set_status64(lo, argp);
err = loop_set_status64(lo, mode, bdev, argp);
break;
case LOOP_GET_STATUS64:
return loop_get_status64(lo, argp);
@@ -1650,8 +1668,9 @@ loop_info64_to_compat(const struct loop_info64 *info64,
}
static int
loop_set_status_compat(struct loop_device *lo,
const struct compat_loop_info __user *arg)
loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
struct block_device *bdev,
const struct compat_loop_info __user *arg)
{
struct loop_info64 info64;
int ret;
@@ -1659,7 +1678,7 @@ loop_set_status_compat(struct loop_device *lo,
ret = loop_info64_from_compat(arg, &info64);
if (ret < 0)
return ret;
return loop_set_status(lo, &info64);
return loop_set_status(lo, mode, bdev, &info64);
}
static int
@@ -1685,7 +1704,7 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
switch(cmd) {
case LOOP_SET_STATUS:
err = loop_set_status_compat(lo,
err = loop_set_status_compat(lo, mode, bdev,
(const struct compat_loop_info __user *)arg);
break;
case LOOP_GET_STATUS: