btrfs: fix NULL dereference on root when tracing inode eviction

[ Upstream commit f157dd661339fc6f5f2b574fe2429c43bd309534 ]

When evicting an inode the first thing we do is to setup tracing for it,
which implies fetching the root's id. But in btrfs_evict_inode() the
root might be NULL, as implied in the next check that we do in
btrfs_evict_inode().

Hence, we either should set the ->root_objectid to 0 in case the root is
NULL, or we move tracing setup after checking that the root is not
NULL. Setting the rootid to 0 at least gives us the possibility to trace
this call even in the case when the root is NULL, so that's the solution
taken here.

Fixes: 1abe9b8a138c ("Btrfs: add initial tracepoint support for btrfs")
Reported-by: syzbot+d991fea1b4b23b1f6bf8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d991fea1b4b23b1f6bf8
Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/trace/events/btrfs.h b/include/trace/events/btrfs.h
index cc880749142838d140e228d0d132ba7deb9f0144..0ca86909ce5bd718c94477ecd7483f39ce59f4d5 100644 (file)
--- a/include/trace/events/btrfs.h
+++ b/include/trace/events/btrfs.h
@@ -223,7 +223,8 @@ DECLARE_EVENT_CLASS(btrfs__inode,
                __entry->generation = BTRFS_I(inode)->generation;
                __entry->last_trans = BTRFS_I(inode)->last_trans;
                __entry->logged_trans = BTRFS_I(inode)->logged_trans;
-               __entry->root_objectid = btrfs_root_id(BTRFS_I(inode)->root);
+               __entry->root_objectid = BTRFS_I(inode)->root ?
+                                        btrfs_root_id(BTRFS_I(inode)->root) : 0;
        ),
 
        TP_printk_btrfs("root=%llu(%s) gen=%llu ino=%llu blocks=%llu "