Re: [PATCH v17 10/13] namei: LOOKUP_{IN_ROOT,BENEATH}: permit limited ".." resolution
From: Al Viro <viro@zeniv.linux.org.uk>
Date: 2019-11-25 00:37:46
Also in:
linux-alpha, linux-api, linux-arch
On Sun, Nov 17, 2019 at 12:17:10PM +1100, Aleksa Sarai wrote:
+ if (unlikely(nd->flags & LOOKUP_IS_SCOPED)) {
+ /*
+ * If there was a racing rename or mount along our
+ * path, then we can't be sure that ".." hasn't jumped
+ * above nd->root (and so userspace should retry or use
+ * some fallback).
+ */
+ if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
+ return -EAGAIN;
+ if (unlikely(read_seqretry(&rename_lock, nd->r_seq)))
+ return -EAGAIN;
+ }Looks like excessive barriers to me - it's rmb check mount_lock.sequence rmb check rename_lock.sequence
quoted hunk ↗ jump to hunk
@@ -2266,6 +2274,10 @@ static const char *path_init(struct nameidata *nd, unsigned flags) nd->last_type = LAST_ROOT; /* if there are only slashes... */ nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT; nd->depth = 0; + + nd->m_seq = read_seqbegin(&mount_lock); + nd->r_seq = read_seqbegin(&rename_lock);
Same here, pretty much (fetch/rmb/fetch/rmb)