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unfuck proc_sysctl ->d_compare()

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a) struct inode is not going to be freed under ->d_compare();
however, the thing PROC_I(inode)->sysctl points to just might.
Fortunately, it's enough to make freeing that sucker delayed,
provided that we don't step on its ->unregistering, clear
the pointer to it in PROC_I(inode) before dropping the reference
and check if it's NULL in ->d_compare().

b) I'm not sure that we *can* walk into NULL inode here (we recheck
dentry->seq between verifying that it's still hashed / fetching
dentry->d_inode and passing it to ->d_compare() and there's no
negative hashed dentries in /proc/sys/*), but if we can walk into
that, we really should not have ->d_compare() return 0 on it!
Said that, I really suspect that this check can be simply killed.
Nick?

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2011-03-08 01:25:28 -05:00
parent 1858efd471
commit dfef6dcd35
4 changed files with 31 additions and 13 deletions
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7
fs/proc/proc_sysctl.c
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@@ -408,15 +408,18 @@ static int proc_sys_compare(const struct dentry *parent,
const struct dentry *dentry, const struct inode *inode,
unsigned int len, const char *str, const struct qstr *name)
{
struct ctl_table_header *head;
/* Although proc doesn't have negative dentries, rcu-walk means
* that inode here can be NULL */
/* AV: can it, indeed? */
if (!inode)
return 0;
return 1;
if (name->len != len)
return 1;
if (memcmp(name->name, str, len))
return 1;
return !sysctl_is_seen(PROC_I(inode)->sysctl);
head = rcu_dereference(PROC_I(inode)->sysctl);
return !head || !sysctl_is_seen(head);
}
static const struct dentry_operations proc_sys_dentry_operations = {