afs: Fix possible oops in afs_lookup trace event

The afs_lookup trace event can cause the following:

[  216.576777] BUG: kernel NULL pointer dereference, address: 000000000000023b
[  216.576803] #PF: supervisor read access in kernel mode
[  216.576813] #PF: error_code(0x0000) - not-present page
...
[  216.576913] RIP: 0010:trace_event_raw_event_afs_lookup+0x9e/0x1c0 [kafs]

If the inode from afs_do_lookup() is an error other than ENOENT, or if it
is ENOENT and afs_try_auto_mntpt() returns an error, the trace event will
try to dereference the error pointer as a valid pointer.

Use IS_ERR_OR_NULL to only pass a valid pointer for the trace, or NULL.

Ideally the trace would include the error value, but for now just avoid
the oops.

Fixes: 5833e6942c84 ("afs: Add more tracepoints")
Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 81207dc3c9977892ece421851666eadf8e818321..139b4e3cc9464d81a72e980d5fc0077a5c8425c4 100644 (file)
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -959,7 +959,8 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
                                 inode ? AFS_FS_I(inode) : NULL);
        } else {
                trace_afs_lookup(dvnode, &dentry->d_name,
-                                inode ? AFS_FS_I(inode) : NULL);
+                                IS_ERR_OR_NULL(inode) ? NULL
+                                : AFS_FS_I(inode));
        }
        return d;
 }