Messages in this thread Patch in this message | | | From | Trond Myklebust <> | Subject | Re: [PATCH] nfs: callback_proc: fix an incorrect NULL check on list iterator | Date | Mon, 28 Mar 2022 13:24:57 +0000 |
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On Mon, 2022-03-28 at 09:43 +0800, Xiaomeng Tong wrote: > On Sun, 27 Mar 2022 15:20:42 +0000, Trond Myklebust wrote: > > On Sun, 2022-03-27 at 16:02 +0800, Xiaomeng Tong wrote: > > > The bug is here: > > > if (!server || > > > server->pnfs_curr_ld->id != dev->cbd_layout_type) { > > > > > > The list iterator value 'server' will *always* be set and non- > > > NULL > > > by list_for_each_entry_rcu, so it is incorrect to assume that the > > > iterator value will be NULL if the list is empty or no element is > > > found (In fact, it will be a bogus pointer to an invalid struct > > > object containing the HEAD, which is used for above check at next > > > outer loop). Otherwise it may bypass the check in theory (iif > > > server->pnfs_curr_ld->id == dev->cbd_layout_type, 'server' now is > > > a bogus pointer) and lead to invalid memory access passing the > > > check. > > > > > > To fix the bug, use a new variable 'iter' as the list iterator, > > > while use the original variable 'server' as a dedicated pointer > > > to > > > point to the found element. > > > > > > Cc: stable@vger.kernel.org > > > Fixes: 1be5683b03a76 ("pnfs: CB_NOTIFY_DEVICEID") > > > Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com> > > > --- > > > fs/nfs/callback_proc.c | 9 +++++---- > > > 1 file changed, 5 insertions(+), 4 deletions(-) > > > > > > diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c > > > index c343666d9a42..84779785dc8d 100644 > > > --- a/fs/nfs/callback_proc.c > > > +++ b/fs/nfs/callback_proc.c > > > @@ -361,7 +361,7 @@ __be32 nfs4_callback_devicenotify(void *argp, > > > void *resp, > > > uint32_t i; > > > __be32 res = 0; > > > struct nfs_client *clp = cps->clp; > > > - struct nfs_server *server = NULL; > > > + struct nfs_server *server = NULL, *iter; > > > > > > if (!clp) { > > > res = cpu_to_be32(NFS4ERR_OP_NOT_IN_SESSION); > > > @@ -374,10 +374,11 @@ __be32 nfs4_callback_devicenotify(void > > > *argp, > > > void *resp, > > > if (!server || > > > server->pnfs_curr_ld->id != dev- > > > >cbd_layout_type) > > > { > > > rcu_read_lock(); > > > - list_for_each_entry_rcu(server, &clp- > > > > cl_superblocks, client_link) > > > - if (server->pnfs_curr_ld && > > > - server->pnfs_curr_ld->id == > > > dev- > > > > cbd_layout_type) { > > > + list_for_each_entry_rcu(iter, &clp- > > > > cl_superblocks, client_link) > > > + if (iter->pnfs_curr_ld && > > > + iter->pnfs_curr_ld->id == > > > dev- > > > > cbd_layout_type) { > > > rcu_read_unlock(); > > > + server = iter; > > > > Hmm... We're not holding any locks on the super block for 'iter' > > here, > > so nothing is preventing it from going away while we're. > > > > ok, i am not a 'rcu lock' expert, i will make it hold the > rcu_read_lock() > if necessary. > > > Given that we really only want a pointer to the struct > > pnfs_layoutdriver_type anyway, why not just convert the code to > > save a > > pointer to that (and do it while holding the rcu_read_lock())? > > > > Maybe it's not that simple. If you only save a pointer to that and > still > use 'server' as the list iterator of list_for_each_entry_rcu, there > could > be problem. > > I.e., if no element found in list_for_each_entry_rcu in the first > outer > 'for' loop, and now 'server' is a bogus pointer to an invalid struct, > and > continue to go into the second outer 'for' loop, and the check below > will > lead to invalid memory access (server->pnfs_curr_ld->id), even can > potentialy > be bypassed with crafted data to make the condition false and > mistakely run > nfs4_delete_deviceid(server->pnfs_curr_ld, clp, &dev->cbd_dev_id); > with bogus > 'server'. > > if (!server || > server->pnfs_curr_ld->id != dev->cbd_layout_type) { > > > The struct pnfs_layoutdriver is always expected to be a statically > > allocated structure, so it won't go away as long as the pNFS driver > > module remains loaded. >
Let's just do the following.
8<----------------------------------------------- From 7c9d845f0612e5bcd23456a2ec43be8ac43458f1 Mon Sep 17 00:00:00 2001 From: Trond Myklebust <trond.myklebust@hammerspace.com> Date: Mon, 28 Mar 2022 08:36:34 -0400 Subject: [PATCH] NFSv4/pNFS: Fix another issue with a list iterator pointing to the head
In nfs4_callback_devicenotify(), if we don't find a matching entry for the deviceid, we're left with a pointer to 'struct nfs_server' that actually points to the list of super blocks associated with our struct nfs_client. Furthermore, even if we have a valid pointer, nothing pins the super block, and so the struct nfs_server could end up getting freed while we're using it.
Since all we want is a pointer to the struct pnfs_layoutdriver_type, let's skip all the iteration over super blocks, and just use APIs to find the layout driver directly.
Reported-by: Xiaomeng Tong <xiam0nd.tong@gmail.com> Fixes: 1be5683b03a7 ("pnfs: CB_NOTIFY_DEVICEID") Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com> --- fs/nfs/callback_proc.c | 27 +++++++++------------------ fs/nfs/pnfs.c | 11 +++++++++++ fs/nfs/pnfs.h | 2 ++ 3 files changed, 22 insertions(+), 18 deletions(-)
diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c index 39d1ec870d90..c8520284dda7 100644 --- a/fs/nfs/callback_proc.c +++ b/fs/nfs/callback_proc.c @@ -358,12 +358,11 @@ __be32 nfs4_callback_devicenotify(void *argp, void *resp, struct cb_process_state *cps) { struct cb_devicenotifyargs *args = argp; + const struct pnfs_layoutdriver_type *ld = NULL; uint32_t i; __be32 res = 0; - struct nfs_client *clp = cps->clp; - struct nfs_server *server = NULL; - if (!clp) { + if (!cps->clp) { res = cpu_to_be32(NFS4ERR_OP_NOT_IN_SESSION); goto out; } @@ -371,23 +370,15 @@ __be32 nfs4_callback_devicenotify(void *argp, void *resp, for (i = 0; i < args->ndevs; i++) { struct cb_devicenotifyitem *dev = &args->devs[i]; - if (!server || - server->pnfs_curr_ld->id != dev->cbd_layout_type) { - rcu_read_lock(); - list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) - if (server->pnfs_curr_ld && - server->pnfs_curr_ld->id == dev->cbd_layout_type) { - rcu_read_unlock(); - goto found; - } - rcu_read_unlock(); - continue; + if (!ld || ld->id != dev->cbd_layout_type) { + pnfs_put_layoutdriver(ld); + ld = pnfs_find_layoutdriver(dev->cbd_layout_type); + if (!ld) + continue; } - - found: - nfs4_delete_deviceid(server->pnfs_curr_ld, clp, &dev->cbd_dev_id); + nfs4_delete_deviceid(ld, cps->clp, &dev->cbd_dev_id); } - + pnfs_put_layoutdriver(ld); out: kfree(args->devs); return res; diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c index de318bb5d349..856c962273c7 100644 --- a/fs/nfs/pnfs.c +++ b/fs/nfs/pnfs.c @@ -92,6 +92,17 @@ find_pnfs_driver(u32 id) return local; } +const struct pnfs_layoutdriver_type *pnfs_find_layoutdriver(u32 id) +{ + return find_pnfs_driver(id); +} + +void pnfs_put_layoutdriver(const struct pnfs_layoutdriver_type *ld) +{ + if (ld) + module_put(ld->owner); +} + void unset_pnfs_layoutdriver(struct nfs_server *nfss) { diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h index f4d7548d67b2..07f11489e4e9 100644 --- a/fs/nfs/pnfs.h +++ b/fs/nfs/pnfs.h @@ -234,6 +234,8 @@ struct pnfs_devicelist { extern int pnfs_register_layoutdriver(struct pnfs_layoutdriver_type *); extern void pnfs_unregister_layoutdriver(struct pnfs_layoutdriver_type *); +extern const struct pnfs_layoutdriver_type *pnfs_find_layoutdriver(u32 id); +extern void pnfs_put_layoutdriver(const struct pnfs_layoutdriver_type *ld); /* nfs4proc.c */ extern size_t max_response_pages(struct nfs_server *server); -- 2.35.1
-- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@hammerspace.com
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