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NFSD: fix possible oops when nfsd/pool_stats is closed.

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If /proc/fs/nfsd/pool_stats is open when the last nfsd thread exits, then
when the file is closed a NULL pointer is dereferenced.
This is because nfsd_pool_stats_release() assumes that the
pointer to the svc_serv cannot become NULL while a reference is held.

This used to be the case but a recent patch split nfsd_last_thread() out
from nfsd_put(), and clearing the pointer is done in nfsd_last_thread().

This is easily reproduced by running
   rpc.nfsd 8 ; ( rpc.nfsd 0;true) < /proc/fs/nfsd/pool_stats

Fortunately nfsd_pool_stats_release() has easy access to the svc_serv
pointer, and so can call svc_put() on it directly.

Fixes: 9f28a971ee ("nfsd: separate nfsd_last_thread() from nfsd_put()")
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
NeilBrown 2023-09-12 11:25:00 +10:00 committed by Chuck Lever
parent fdd2630a73
commit 88956eabfd
1 changed files with 3 additions and 2 deletions
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5
fs/nfsd/nfssvc.c
View file

@ -1082,11 +1082,12 @@ int nfsd_pool_stats_open(struct inode *inode, struct file *file)
int nfsd_pool_stats_release(struct inode *inode, struct file *file)
{
struct seq_file *seq = file->private_data;
struct svc_serv *serv = seq->private;
int ret = seq_release(inode, file);
struct net *net = inode->i_sb->s_fs_info;
mutex_lock(&nfsd_mutex);
nfsd_put(net);
svc_put(serv);
mutex_unlock(&nfsd_mutex);
return ret;
}