[PATCH 4.20 102/183] afs: Dont set vnode->cb_s_break in afs_validate()

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 4882a27cec24319d10f95e978ecc80050e3e3e15 ]

A cb_interest record is not necessarily attached to the vnode on entry to
afs_validate(), which can cause an oops when we try to bring the vnode's
cb_s_break up to date in the default case (ie. no current callback promise
and the vnode has not been deleted).

Fix this by simply removing the line, as vnode->cb_s_break will be set when
needed by afs_register_server_cb_interest() when we next get a callback
promise from RPC call.

The oops looks something like:

    BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
    ...
    RIP: 0010:afs_validate+0x66/0x250 [kafs]
    ...
    Call Trace:
     afs_d_revalidate+0x8d/0x340 [kafs]
     ? __d_lookup+0x61/0x150
     lookup_dcache+0x44/0x70
     ? lookup_dcache+0x44/0x70
     __lookup_hash+0x24/0xa0
     do_unlinkat+0x11d/0x2c0
     __x64_sys_unlink+0x23/0x30
     do_syscall_64+0x4d/0xf0
     entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: ae3b7361dc0e ("afs: Fix validation/callback interaction")
Signed-off-by: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/afs/inode.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 6b17d36204142..211343831c304 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -414,7 +414,6 @@ int afs_validate(struct afs_vnode *vnode, struct key *key)
 	} else if (test_bit(AFS_VNODE_DELETED, &vnode->flags)) {
 		valid = true;
 	} else {
-		vnode->cb_s_break = vnode->cb_interest->server->cb_s_break;
 		vnode->cb_v_break = vnode->volume->cb_v_break;
 		valid = false;
 	}
-- 
2.19.1