udf_expand_file_adinicb() calls directly ->writepage to write data expanded into a page. This however misses to setup inode for writeback properly and so we can crash on inode->i_wb dereference when submitting page for IO like:

BUG: kernel NULL pointer dereference, address: 0000000000000158 #PF: supervisor read access in kernel mode ... <TASK> __folio_start_writeback+0x2ac/0x350 __block_write_full_page+0x37d/0x490 udf_expand_file_adinicb+0x255/0x400 [udf] udf_file_write_iter+0xbe/0x1b0 [udf] new_sync_write+0x125/0x1c0 vfs_write+0x28e/0x400

Fix the problem by marking the page dirty and going through the standard writeback path to write the page. Strictly speaking we would not even have to write the page but we want to catch e.g. ENOSPC errors early.

Reported-by: butt3rflyh4ck butterflyhuangxx@gmail.com CC: stable@vger.kernel.org Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") Signed-off-by: Jan Kara jack@suse.cz --- fs/udf/inode.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c index 1d6b7a50736b..d6aa506b6b58 100644 --- a/fs/udf/inode.c +++ b/fs/udf/inode.c @@ -258,10 +258,6 @@ int udf_expand_file_adinicb(struct inode *inode) char *kaddr; struct udf_inode_info *iinfo = UDF_I(inode); int err; - struct writeback_control udf_wbc = { - .sync_mode = WB_SYNC_NONE, - .nr_to_write = 1, - };

WARN_ON_ONCE(!inode_is_locked(inode)); if (!iinfo->i_lenAlloc) { @@ -305,8 +301,10 @@ int udf_expand_file_adinicb(struct inode *inode) iinfo->i_alloc_type = ICBTAG_FLAG_AD_LONG; /* from now on we have normal address_space methods */ inode->i_data.a_ops = &udf_aops; + set_page_dirty(page); + unlock_page(page); up_write(&iinfo->i_data_sem); - err = inode->i_data.a_ops->writepage(page, &udf_wbc); + err = filemap_fdatawrite(inode->i_mapping); if (err) { /* Restore everything back so that we don't lose data... */ lock_page(page);