Some sysctl tables can provide an is_seen() function which reports if
the sysctl should be visible to the current process. This is currently
used to cause d_compare to fail for invisible sysctls.
This technique might have worked in 2.6.26 when it was implemented, but
it cannot work now. In particular if ->d_compare always fails for a
particular name, then d_alloc_parallel() will always create a new dentry
and pass it to lookup() resulting in a new inode for every lookup. I
tested this by changing sysctl_is_seen() to always return 0. When
all sysctls were still visible and repeated lookups (ls -li) reported
different inode numbers.
This patch discards proc_sys_compare (the d_compare function) and
instead adds the is_seen functionality into proc_sys_revalidate (the
d_revalidate function). If the sysctl table is unregistering, 0 is
returned. Otherwise if is_seen() exists but fails, -ENOENT is returned.
The rcu_dereference() and RCU_INIT_POINTER() for ->sysctl are removed as
the field is not rcu-managed. It is only changed when the inode is
created and when it is evicted, and in these cases there can be no
possible concurrent access.
Signed-off-by: NeilBrown <neil@xxxxxxxxxx>
---
fs/proc/inode.c | 2 +-
fs/proc/proc_sysctl.c | 35 ++++-------------------------------
2 files changed, 5 insertions(+), 32 deletions(-)
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index a3eb3b740f76..c3991dd314d9 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -42,7 +42,7 @@ static void proc_evict_inode(struct inode *inode)
head = ei->sysctl;
if (head) {
- RCU_INIT_POINTER(ei->sysctl, NULL);
+ ei->sysctl = NULL;
proc_sys_evict_inode(inode, head);
}
}
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index cc9d74a06ff0..dbf652b50909 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -884,21 +884,15 @@ static const struct inode_operations proc_sys_dir_operations = {
.getattr = proc_sys_getattr,
};
-static int proc_sys_revalidate(struct inode *dir, const struct qstr *name,
- struct dentry *dentry, unsigned int flags)
-{
- if (flags & LOOKUP_RCU)
- return -ECHILD;
- return !PROC_I(d_inode(dentry))->sysctl->unregistering;
-}
-
static int proc_sys_delete(const struct dentry *dentry)
{
return !!PROC_I(d_inode(dentry))->sysctl->unregistering;
}
-static int sysctl_is_seen(struct ctl_table_header *p)
+static int proc_sys_revalidate(struct inode *dir, const struct qstr *name,
+ struct dentry *dentry, unsigned int flags)
{
+ struct ctl_table_header *p = PROC_I(d_inode(dentry))->sysctl;
struct ctl_table_set *set = p->set;
int res;
spin_lock(&sysctl_lock);
@@ -907,35 +901,14 @@ static int sysctl_is_seen(struct ctl_table_header *p)
else if (!set->is_seen)
res = 1;
else
- res = set->is_seen(set);
+ res = set->is_seen(set) ? 1 : -ENOENT;
spin_unlock(&sysctl_lock);
return res;
}
-static int proc_sys_compare(const struct dentry *dentry,
- unsigned int len, const char *str, const struct qstr *name)
-{
- struct ctl_table_header *head;
- struct inode *inode;
-
- /* Although proc doesn't have negative dentries, rcu-walk means
- * that inode here can be NULL */
- /* AV: can it, indeed? */
- inode = d_inode_rcu(dentry);
- if (!inode)
- return 1;
- if (name->len != len)
- return 1;
- if (memcmp(name->name, str, len))
- return 1;
- head = rcu_dereference(PROC_I(inode)->sysctl);
- return !head || !sysctl_is_seen(head);
-}
-
static const struct dentry_operations proc_sys_dentry_operations = {
.d_revalidate = proc_sys_revalidate,
.d_delete = proc_sys_delete,
- .d_compare = proc_sys_compare,
};
static struct ctl_dir *find_subdir(struct ctl_dir *dir,
--
2.49.0
