[PATCH] proc/sysctl: don't return ENOMEM on lookup when a table is unregistering

[Ivan Delalande]

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 removed, which confuses our configuration daemon.

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

Fixes: ace0c791e6c3 ("proc/sysctl: Don't grab i_lock under sysctl_lock.")
Cc: sta...@vger.kernel.org
Signed-off-by: Ivan Delalande <col...@arista.com>
---
 fs/proc/proc_sysctl.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 89921a0d2ebb..834be5bc3d07 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -474,7 +474,7 @@ static struct inode *proc_sys_make_inode(struct super_block 
*sb,
        if (unlikely(head->unregistering)) {
                spin_unlock(&sysctl_lock);
                iput(inode);
-               inode = NULL;
+               inode = ERR_PTR(-ENOENT);
                goto out;
        }
        ei->sysctl = head;
@@ -549,10 +549,11 @@ static struct dentry *proc_sys_lookup(struct inode *dir, 
struct dentry *dentry,
                        goto out;
        }
 
-       err = ERR_PTR(-ENOMEM);
        inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
-       if (!inode)
+       if (IS_ERR_OR_NULL(inode)) {
+               err = inode ? ERR_CAST(inode) : ERR_PTR(-ENOMEM);
                goto out;
+       }
 
        d_set_d_op(dentry, &proc_sys_dentry_operations);
        err = d_splice_alias(inode, dentry);
@@ -685,7 +686,7 @@ static bool proc_sys_fill_cache(struct file *file,
                if (d_in_lookup(child)) {
                        struct dentry *res;
                        inode = proc_sys_make_inode(dir->d_sb, head, table);
-                       if (!inode) {
+                       if (IS_ERR_OR_NULL(inode)) {
                                d_lookup_done(child);
                                dput(child);
                                return false;
-- 
2.20.0