From: "Darrick J. Wong" djwong@kernel.org

commit c0e473a0d226479e8e925d5ba93f751d8df628e9 upstream.

With the new large sector size support, it's now the case that set_blocksize can change i_blksize and the folio order in a manner that conflicts with a concurrent reader and causes a kernel crash.

Specifically, let's say that udev-worker calls libblkid to detect the labels on a block device. The read call can create an order-0 folio to read the first 4096 bytes from the disk. But then udev is preempted.

Next, someone tries to mount an 8k-sectorsize filesystem from the same block device. The filesystem calls set_blksize, which sets i_blksize to 8192 and the minimum folio order to 1.

Now udev resumes, still holding the order-0 folio it allocated. It then tries to schedule a read bio and do_mpage_readahead tries to create bufferheads for the folio. Unfortunately, blocks_per_folio == 0 because the page size is 4096 but the blocksize is 8192 so no bufferheads are attached and the bh walk never sets bdev. We then submit the bio with a NULL block device and crash.

Therefore, truncate the page cache after flushing but before updating i_blksize. However, that's not enough -- we also need to lock out file IO and page faults during the update. Take both the i_rwsem and the invalidate_lock in exclusive mode for invalidations, and in shared mode for read/write operations.

I don't know if this is the correct fix, but xfs/259 found it.

Signed-off-by: Darrick J. Wong djwong@kernel.org Reviewed-by: Christoph Hellwig hch@lst.de Reviewed-by: Luis Chamberlain mcgrof@kernel.org Tested-by: Shin'ichiro Kawasaki shinichiro.kawasaki@wdc.com Link: https://lore.kernel.org/r/174543795699.4139148.2086129139322431423.stgit@fro... Signed-off-by: Jens Axboe axboe@kernel.dk [use bdev->bd_inode instead] Signed-off-by: Mahmoud Adam mngyadam@amazon.de --- Fixes CVE-2025-38073.

block/bdev.c | 17 +++++++++++++++++ block/blk-zoned.c | 5 ++++- block/fops.c | 16 ++++++++++++++++ block/ioctl.c | 6 ++++++ 4 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/block/bdev.c b/block/bdev.c index 5a54977518eeae..a8357b72a27b86 100644 --- a/block/bdev.c +++ b/block/bdev.c @@ -147,9 +147,26 @@ int set_blocksize(struct block_device *bdev, int size)

/* Don't change the size if it is same as current */ if (bdev->bd_inode->i_blkbits != blksize_bits(size)) { + /* + * Flush and truncate the pagecache before we reconfigure the + * mapping geometry because folio sizes are variable now. If a + * reader has already allocated a folio whose size is smaller + * than the new min_order but invokes readahead after the new + * min_order becomes visible, readahead will think there are + * "zero" blocks per folio and crash. Take the inode and + * invalidation locks to avoid racing with + * read/write/fallocate. + */ + inode_lock(bdev->bd_inode); + filemap_invalidate_lock(bdev->bd_inode->i_mapping); + sync_blockdev(bdev); + kill_bdev(bdev); + bdev->bd_inode->i_blkbits = blksize_bits(size); kill_bdev(bdev); + filemap_invalidate_unlock(bdev->bd_inode->i_mapping); + inode_unlock(bdev->bd_inode); } return 0; } diff --git a/block/blk-zoned.c b/block/blk-zoned.c index 619ee41a51cc8c..644bfa1f6753ea 100644 --- a/block/blk-zoned.c +++ b/block/blk-zoned.c @@ -401,6 +401,7 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, blk_mode_t mode, op = REQ_OP_ZONE_RESET;

/* Invalidate the page cache, including dirty pages. */ + inode_lock(bdev->bd_inode); filemap_invalidate_lock(bdev->bd_inode->i_mapping); ret = blkdev_truncate_zone_range(bdev, mode, &zrange); if (ret) @@ -423,8 +424,10 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, blk_mode_t mode, GFP_KERNEL);

fail: - if (cmd == BLKRESETZONE) + if (cmd == BLKRESETZONE) { filemap_invalidate_unlock(bdev->bd_inode->i_mapping); + inode_unlock(bdev->bd_inode); + }

return ret; } diff --git a/block/fops.c b/block/fops.c index 7c257eb3564d0c..088143fa9ac9e1 100644 --- a/block/fops.c +++ b/block/fops.c @@ -681,7 +681,14 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from) ret = direct_write_fallback(iocb, from, ret, blkdev_buffered_write(iocb, from)); } else { + /* + * Take i_rwsem and invalidate_lock to avoid racing with + * set_blocksize changing i_blkbits/folio order and punching + * out the pagecache. + */ + inode_lock_shared(bd_inode); ret = blkdev_buffered_write(iocb, from); + inode_unlock_shared(bd_inode); }

if (ret > 0) @@ -693,6 +700,7 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from) static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to) { struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host); + struct inode *bd_inode = bdev->bd_inode; loff_t size = bdev_nr_bytes(bdev); loff_t pos = iocb->ki_pos; size_t shorted = 0; @@ -728,7 +736,13 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to) goto reexpand; }

+ /* + * Take i_rwsem and invalidate_lock to avoid racing with set_blocksize + * changing i_blkbits/folio order and punching out the pagecache. + */ + inode_lock_shared(bd_inode); ret = filemap_read(iocb, to, ret); + inode_unlock_shared(bd_inode);

reexpand: if (unlikely(shorted)) @@ -771,6 +785,7 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start, if ((start | len) & (bdev_logical_block_size(bdev) - 1)) return -EINVAL;

+ inode_lock(inode); filemap_invalidate_lock(inode->i_mapping);

/* @@ -811,6 +826,7 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,

fail: filemap_invalidate_unlock(inode->i_mapping); + inode_unlock(inode); return error; }

diff --git a/block/ioctl.c b/block/ioctl.c index 231537f79a8cb4..024767fa1e52d5 100644 --- a/block/ioctl.c +++ b/block/ioctl.c @@ -114,6 +114,7 @@ static int blk_ioctl_discard(struct block_device *bdev, blk_mode_t mode, end > bdev_nr_bytes(bdev)) return -EINVAL;

+ inode_lock(inode); filemap_invalidate_lock(inode->i_mapping); err = truncate_bdev_range(bdev, mode, start, end - 1); if (err) @@ -121,6 +122,7 @@ static int blk_ioctl_discard(struct block_device *bdev, blk_mode_t mode, err = blkdev_issue_discard(bdev, start >> 9, len >> 9, GFP_KERNEL); fail: filemap_invalidate_unlock(inode->i_mapping); + inode_unlock(inode); return err; }

@@ -146,12 +148,14 @@ static int blk_ioctl_secure_erase(struct block_device *bdev, blk_mode_t mode, end > bdev_nr_bytes(bdev)) return -EINVAL;

+ inode_lock(bdev->bd_inode); filemap_invalidate_lock(bdev->bd_inode->i_mapping); err = truncate_bdev_range(bdev, mode, start, end - 1); if (!err) err = blkdev_issue_secure_erase(bdev, start >> 9, len >> 9, GFP_KERNEL); filemap_invalidate_unlock(bdev->bd_inode->i_mapping); + inode_unlock(bdev->bd_inode); return err; }

@@ -184,6 +188,7 @@ static int blk_ioctl_zeroout(struct block_device *bdev, blk_mode_t mode, return -EINVAL;

/* Invalidate the page cache, including dirty pages */ + inode_lock(inode); filemap_invalidate_lock(inode->i_mapping); err = truncate_bdev_range(bdev, mode, start, end); if (err) @@ -194,6 +199,7 @@ static int blk_ioctl_zeroout(struct block_device *bdev, blk_mode_t mode,

fail: filemap_invalidate_unlock(inode->i_mapping); + inode_unlock(inode); return err; }