Re: [PATCH 1/1] NFSD: fix use-after-free in __nfs42_ssc_open()
From: Jeff Layton <jlayton@kernel.org>
Date: 2022-12-12 12:22:21
On Sun, 2022-12-11 at 11:22 -0800, Dai Ngo wrote:
quoted hunk ↗ jump to hunk
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. Reported-by: Xingyuan Mo <redacted> Signed-off-by: Dai Ngo <dai.ngo@oracle.com> --- fs/nfsd/nfs4proc.c | 23 +++++++---------------- 1 file changed, 7 insertions(+), 16 deletions(-)diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c index 8beb2bc4c328..756e42cf0d01 100644 --- a/fs/nfsd/nfs4proc.c +++ b/fs/nfsd/nfs4proc.c@@ -1463,13 +1463,6 @@ 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. *@@ -1572,11 +1565,6 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct file *filp, { } -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)@@ -1762,7 +1750,8 @@ static int nfsd4_do_async_copy(void *data) struct file *filp; filp = nfs42_ssc_open(copy->ss_mnt, ©->c_fh, - ©->stateid); + ©->stateid); + if (IS_ERR(filp)) { switch (PTR_ERR(filp)) { case -EBADF:@@ -1771,7 +1760,7 @@ static int nfsd4_do_async_copy(void *data) default: nfserr = nfserr_offload_denied; } - nfsd4_interssc_disconnect(copy->ss_mnt); + /* ss_mnt will be unmounted by the laundromat */ goto do_callback; } nfserr = nfsd4_do_copy(copy, filp, copy->nf_dst->nf_file,@@ -1852,8 +1841,10 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, if (async_copy) cleanup_async_copy(async_copy); status = nfserrno(-ENOMEM); - if (nfsd4_ssc_is_inter(copy)) - nfsd4_interssc_disconnect(copy->ss_mnt); + /* + * source's vfsmount of inter-copy will be unmounted + * by the laundromat + */ goto out; }
This looks reasonable at first glance, but I have some concerns with the
refcounting around ss_mnt elsewhere in this code. nfsd4_ssc_setup_dul
looks for an existing connection and bumps the ni->nsui_refcnt if it
finds one.
But then later, nfsd4_cleanup_inter_ssc has a couple of cases where it
just does a bare mntput:
if (!nn) {
mntput(ss_mnt);
return;
}
...
if (!found) {
mntput(ss_mnt);
return;
}
The first one looks bogus. Can net_generic return NULL? If so how, and
why is it not a problem elsewhere in the kernel?
For the second case, if the ni is no longer on the list, where did the
extra ss_mnt reference come from? Maybe that should be a WARN_ON or
BUG_ON?
--
Jeff Layton [off-list ref]