netfs: Fix netfs_page_mkwrite() to check folio->mapping is valid

Fix netfs_page_mkwrite() to check that folio->mapping is valid once it has
taken the folio lock (as filemap_page_mkwrite() does).  Without this,
generic/247 occasionally oopses with something like the following:

    BUG: kernel NULL pointer dereference, address: 0000000000000000
    #PF: supervisor read access in kernel mode
    #PF: error_code(0x0000) - not-present page

    RIP: 0010:trace_event_raw_event_netfs_folio+0x61/0xc0
    ...
    Call Trace:
     <TASK>
     ? __die_body+0x1a/0x60
     ? page_fault_oops+0x6e/0xa0
     ? exc_page_fault+0xc2/0xe0
     ? asm_exc_page_fault+0x22/0x30
     ? trace_event_raw_event_netfs_folio+0x61/0xc0
     trace_netfs_folio+0x39/0x40
     netfs_page_mkwrite+0x14c/0x1d0
     do_page_mkwrite+0x50/0x90
     do_pte_missing+0x184/0x200
     __handle_mm_fault+0x42d/0x500
     handle_mm_fault+0x121/0x1f0
     do_user_addr_fault+0x23e/0x3c0
     exc_page_fault+0xc2/0xe0
     asm_exc_page_fault+0x22/0x30

This is due to the invalidate_inode_pages2_range() issued at the end of the
DIO write interfering with the mmap'd writes.

Fixes: 102a7e2c598c ("netfs: Allow buffered shared-writeable mmap through netfs_page_mkwrite()")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/780211.1719318546@warthog.procyon.org.uk
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index 07bc1fd4353092acb9697f76b487c59f290a6f6c..270f8ebf832802e2a5e44c1214c3bc9774200195 100644 (file)
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -523,6 +523,7 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
        struct netfs_group *group;
        struct folio *folio = page_folio(vmf->page);
        struct file *file = vmf->vma->vm_file;
+       struct address_space *mapping = file->f_mapping;
        struct inode *inode = file_inode(file);
        struct netfs_inode *ictx = netfs_inode(inode);
        vm_fault_t ret = VM_FAULT_RETRY;
@@ -534,6 +535,11 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
 
        if (folio_lock_killable(folio) < 0)
                goto out;
+       if (folio->mapping != mapping) {
+               folio_unlock(folio);
+               ret = VM_FAULT_NOPAGE;
+               goto out;
+       }
 
        if (folio_wait_writeback_killable(folio)) {
                ret = VM_FAULT_LOCKED;
@@ -549,7 +555,7 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
        group = netfs_folio_group(folio);
        if (group != netfs_group && group != NETFS_FOLIO_COPY_TO_CACHE) {
                folio_unlock(folio);
-               err = filemap_fdatawait_range(inode->i_mapping,
+               err = filemap_fdatawait_range(mapping,
                                              folio_pos(folio),
                                              folio_pos(folio) + folio_size(folio));
                switch (err) {