From 7214e8600eee146b6ea79eb6b7b01b343856a7c6 Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Thu, 10 Jul 2014 14:07:33 -0400 Subject: [PATCH] nfsd: always hold the fi_lock when bumping fi_access refcounts Once we remove the client_mutex, there's an unlikely but possible race that could occur. It will be possible for nfs4_file_put_access to race with nfs4_file_get_access. The refcount will go to zero (briefly) and then bumped back to one. If that happens we set ourselves up for a use-after-free and the potential for a lock to race onto the i_flock list as a filp is being torn down. Ensure that we can safely bump the refcount on the file by holding the fi_lock whenever that's done. The only place it currently isn't is in get_lock_access. In order to ensure atomicity with finding the file, use the find_*_file_locked variants and then call get_lock_access to get new access references on the nfs4_file under the same lock. Signed-off-by: Jeff Layton Reviewed-by: Christoph Hellwig Signed-off-by: J. Bruce Fields --- fs/nfsd/nfs4state.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index 5f7294712ad4..8f320f2f8b84 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -377,6 +377,8 @@ static struct hlist_head file_hashtbl[FILE_HASH_SIZE]; static void __nfs4_file_get_access(struct nfs4_file *fp, u32 access) { + lockdep_assert_held(&fp->fi_lock); + if (access & NFS4_SHARE_ACCESS_WRITE) atomic_inc(&fp->fi_access[O_WRONLY]); if (access & NFS4_SHARE_ACCESS_READ) @@ -386,6 +388,8 @@ __nfs4_file_get_access(struct nfs4_file *fp, u32 access) static __be32 nfs4_file_get_access(struct nfs4_file *fp, u32 access) { + lockdep_assert_held(&fp->fi_lock); + /* Does this access mode make sense? */ if (access & ~NFS4_SHARE_ACCESS_BOTH) return nfserr_inval; @@ -4572,6 +4576,8 @@ static void get_lock_access(struct nfs4_ol_stateid *lock_stp, u32 access) { struct nfs4_file *fp = lock_stp->st_file; + lockdep_assert_held(&fp->fi_lock); + if (test_access(access, lock_stp)) return; __nfs4_file_get_access(fp, access); @@ -4623,6 +4629,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, struct nfs4_openowner *open_sop = NULL; struct nfs4_lockowner *lock_sop = NULL; struct nfs4_ol_stateid *lock_stp; + struct nfs4_file *fp; struct file *filp = NULL; struct file_lock *file_lock = NULL; struct file_lock *conflock = NULL; @@ -4703,20 +4710,25 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, goto out; } + fp = lock_stp->st_file; locks_init_lock(file_lock); switch (lock->lk_type) { case NFS4_READ_LT: case NFS4_READW_LT: - filp = find_readable_file(lock_stp->st_file); + spin_lock(&fp->fi_lock); + filp = find_readable_file_locked(fp); if (filp) get_lock_access(lock_stp, NFS4_SHARE_ACCESS_READ); + spin_unlock(&fp->fi_lock); file_lock->fl_type = F_RDLCK; break; case NFS4_WRITE_LT: case NFS4_WRITEW_LT: - filp = find_writeable_file(lock_stp->st_file); + spin_lock(&fp->fi_lock); + filp = find_writeable_file_locked(fp); if (filp) get_lock_access(lock_stp, NFS4_SHARE_ACCESS_WRITE); + spin_unlock(&fp->fi_lock); file_lock->fl_type = F_WRLCK; break; default: -- 2.34.1