[SRU][Focal/oem-5.14][Jammy/oem-5.17][PATCH] NFSD: fix use-after-free in __nfs42_ssc_open()

[Andrei Gherzan]

From: Dai Ngo <dai.ngo at oracle.com>

Problem caused by source's vfsmount being unmounted but remains
on the delayed unmount list. This happens when nfs42_ssc_open()
return errors.

Fixed by removing nfsd4_interssc_connect(), leave the vfsmount
for the laundromat to unmount when idle time expires.

We don't need to call nfs_do_sb_deactive when nfs42_ssc_open
return errors since the file was not opened so nfs_server->active
was not incremented. Same as in nfsd4_copy, if we fail to
launch nfsd4_do_async_copy thread then there's no need to
call nfs_do_sb_deactive

Reported-by: Xingyuan Mo <hdthky0 at gmail.com>
Signed-off-by: Dai Ngo <dai.ngo at oracle.com>
Tested-by: Xingyuan Mo <hdthky0 at gmail.com>
Signed-off-by: Chuck Lever <chuck.lever at oracle.com>
CVE-2022-20369
(backported from commit 75333d48f92256a0dec91dbf07835e804fc411c0)
[agherzan: 1913cdf56cb5 ("NFSD: Replace boolean fields in
struct nfsd4_copy") requires adaptations for this patch to match the
removed struct fields. For the nfsd4_do_async_copy conflict there are
multiple changes affecting the backport but the code path is simple to
adapt for handling of the nfsd4_interssc_disconnect call.]
Signed-off-by: Andrei Gherzan <andrei.gherzan at canonical.com>
---
 fs/nfsd/nfs4proc.c | 22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index c85522f5ae3a..4c4b4909be24 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1348,13 +1348,6 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
 	return status;
 }
 
-static void
-nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
-{
-	nfs_do_sb_deactive(ss_mnt->mnt_sb);
-	mntput(ss_mnt);
-}
-
 /*
  * Verify COPY destination stateid.
  *
@@ -1457,11 +1450,6 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct nfsd_file *src,
 {
 }
 
-static void
-nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
-{
-}
-
 static struct file *nfs42_ssc_open(struct vfsmount *ss_mnt,
 				   struct nfs_fh *src_fh,
 				   nfs4_stateid *stateid)
@@ -1619,14 +1607,14 @@ static int nfsd4_do_async_copy(void *data)
 		copy->nf_src = kzalloc(sizeof(struct nfsd_file), GFP_KERNEL);
 		if (!copy->nf_src) {
 			copy->nfserr = nfserr_serverfault;
-			nfsd4_interssc_disconnect(copy->ss_mnt);
+			/* ss_mnt will be unmounted by the laundromat */
 			goto do_callback;
 		}
 		copy->nf_src->nf_file = nfs42_ssc_open(copy->ss_mnt, &copy->c_fh,
 					      &copy->stateid);
 		if (IS_ERR(copy->nf_src->nf_file)) {
 			copy->nfserr = nfserr_offload_denied;
-			nfsd4_interssc_disconnect(copy->ss_mnt);
+			/* ss_mnt will be unmounted by the laundromat */
 			goto do_callback;
 		}
 	}
@@ -1711,8 +1699,10 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	if (async_copy)
 		cleanup_async_copy(async_copy);
 	status = nfserrno(-ENOMEM);
-	if (!copy->cp_intra)
-		nfsd4_interssc_disconnect(copy->ss_mnt);
+	/*
+	 * source's vfsmount of inter-copy will be unmounted
+	 * by the laundromat
+	 */
 	goto out;
 }
 
-- 
2.34.1