[PATCH 4.9 21/22] proc/sysctl: dont return ENOMEM on lookup when a table is unregistering

Greg Kroah-Hartman
2018-12-28T12:18:54Z

From: Ivan Delalande <colona@arista.com>

commit ea5751ccd665a2fd1b24f9af81f6167f0718c5f6 upstream.

proc_sys_lookup can fail with ENOMEM instead of ENOENT when the
corresponding sysctl table is being unregistered. In our case we see
this upon opening /proc/sys/net/*/conf files while network interfaces
are being deleted, which confuses our configuration daemon.

The problem was successfully reproduced and this fix tested on v4.9.122
and v4.20-rc6.

v2: return ERR_PTRs in all cases when proc_sys_make_inode fails instead
of mixing them with NULL. Thanks Al Viro for the feedback.

Fixes: ace0c791e6c3 ("proc/sysctl: Don't grab i_lock under sysctl_lock.")
Cc: stable@vger.kernel.org
Signed-off-by: Ivan Delalande <colona@arista.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/proc/proc_sysctl.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -466,7 +466,7 @@ static struct inode *proc_sys_make_inode

inode = new_inode(sb);
if (!inode)
- goto out;
+ return ERR_PTR(-ENOMEM);

inode->i_ino = get_next_ino();

@@ -476,8 +476,7 @@ static struct inode *proc_sys_make_inode
if (unlikely(head->unregistering)) {
spin_unlock(&sysctl_lock);
iput(inode);
- inode = NULL;
- goto out;
+ return ERR_PTR(-ENOENT);
}
ei->sysctl = head;
ei->sysctl_entry = table;
@@ -502,7 +501,6 @@ static struct inode *proc_sys_make_inode
if (root->set_ownership)
root->set_ownership(head, table, &inode->i_uid, &inode->i_gid);

-out:
return inode;
}

@@ -551,10 +549,11 @@ static struct dentry *proc_sys_lookup(st
goto out;
}

- err = ERR_PTR(-ENOMEM);
inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
- if (!inode)
+ if (IS_ERR(inode)) {
+ err = ERR_CAST(inode);
goto out;
+ }

err = NULL;
d_set_d_op(dentry, &proc_sys_dentry_operations);
@@ -687,7 +686,7 @@ static bool proc_sys_fill_cache(struct f
return false;
if (d_in_lookup(child)) {
inode = proc_sys_make_inode(dir->d_sb, head, table);
- if (!inode) {
+ if (IS_ERR(inode)) {
d_lookup_done(child);
dput(child);
return false;