[PATCH] NFS4: Fix NULL deref in nfsd4_lock() by makeing unhash_lockowner()safe to call with NULL arg
From: Jesper Juhl
Date: Sun Jan 29 2012 - 16:29:11 EST
The Coverity checker noticed a path through nfsd4_lock() where we call
release_lockowner(lock_sop); (at the 'out:' label) where 'lock_sop' is
NULL.
That goes bad since release_lockowner() calls unhash_lockowner() which
dereferences its argument.
release_lockowner() also calls nfs4_free_lockowner(), but that's not a
problem since that function just calls kfree() and kmem_cache_free(),
both of which are safe to call with NULL as argument.
There are several ways to fix the bug.
- rework nfsd4_lock() so the call to release_lockowner(NULL) will never happen.
- let release_lockowner() test for NULL and return if given one.
- let unhash_lockowner() test for NULL and return if given one (which makes both it and release_lockowner() safe).
I chose the last option for this patch.
For information, the path Coverity spotted (in defect report 201504) is this:
3950nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
3951 struct nfsd4_lock *lock)
3952{
3953 struct nfs4_openowner *open_sop = NULL;
CID 201504: Explicit null dereferenced (FORWARD_NULL)
Assigning: "lock_sop" = 0.
3954 struct nfs4_lockowner *lock_sop = NULL;
[...]
3964
At conditional (1): "nfsd_debug & 0x10U" taking the true branch.
3965 dprintk("NFSD: nfsd4_lock: start=%Ld length=%Ld\n",
3966 (long long) lock->lk_offset,
3967 (long long) lock->lk_length);
3968
At conditional (2): "check_lock_length(lock->lk_offset, lock->lk_length)" taking the false branch.
3969 if (check_lock_length(lock->lk_offset, lock->lk_length))
[...]
At conditional (3): "status = fh_verify(rqstp, &cstate->current_fh, 32768/*unsigned short*/, 32)" taking the false branch.
3972 if ((status = fh_verify(rqstp, &cstate->current_fh,
[...]
3976 }
3977
3978 nfs4_lock_state();
3979
At conditional (4): "lock->lk_is_new" taking the true branch.
3980 if (lock->lk_is_new) {
[...]
At conditional (5): "nfsd4_has_session(cstate)" taking the true branch.
3988 if (nfsd4_has_session(cstate))
[...]
At conditional (6): "1" taking the true branch.
3994 status = nfserr_stale_clientid;
At conditional (7): "STALE_CLIENTID(&lock->v.new.clientid)" taking the false branch.
3995 if (STALE_CLIENTID(&lock->lk_new_clientid))
3996 goto out;
[...]
At conditional (8): "status" taking the false branch.
4003 if (status)
4004 goto out;
4005 open_sop = openowner(open_stp->st_stateowner);
At conditional (9): "1" taking the true branch.
4006 status = nfserr_bad_stateid;
At conditional (10): "!same_clid(&open_sop->oo_owner.so_client->cl_clientid, &lock->v.new.clientid)" taking the false branch.
4007 if (!same_clid(&open_sop->oo_owner.so_client->cl_clientid,
4008 &lock->v.new.clientid))
4009 goto out;
4010 status = lookup_or_create_lock_state(cstate, open_stp, lock,
4011 &lock_stp, &new_state);
At conditional (11): "status" taking the true branch.
4012 if (status)
4013 goto out;
[...]
4098out:
At conditional (12): "status" taking the true branch.
At conditional (13): "new_state" taking the true branch.
4099 if (status && new_state)
Passing null variable "lock_sop" to function "release_lockowner", which dereferences it. [show details]
4100 release_lockowner(lock_sop);
4101 if (!cstate->replay_owner)
4102 nfs4_unlock_state();
4103 return status;
4104}
Signed-off-by: Jesper Juhl <jj@xxxxxxxxxxxxx>
---
fs/nfsd/nfs4state.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
Patch is compile tested only.
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index e8c98f0..730a73b 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -520,6 +520,8 @@ static void unhash_lockowner(struct nfs4_lockowner *lo)
{
struct nfs4_ol_stateid *stp;
+ if (!lo)
+ return;
list_del(&lo->lo_owner.so_strhash);
list_del(&lo->lo_perstateid);
list_del(&lo->lo_owner_ino_hash);
--
1.7.8.4
--
Jesper Juhl <jj@xxxxxxxxxxxxx> http://www.chaosbits.net/
Don't top-post http://www.catb.org/jargon/html/T/top-post.html
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