From: Al Viro <viro@ZenIV.linux.org.uk>
To: NeilBrown <neilb@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [RFC][PATCHSET] non-recursive link_path_walk() and reducing stack footprint
Date: Wed, 22 Apr 2015 21:12:38 +0100 [thread overview]
Message-ID: <20150422201238.GW889@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20150422180702.GA15209@ZenIV.linux.org.uk>
On Wed, Apr 22, 2015 at 07:07:59PM +0100, Al Viro wrote:
> And one more: may_follow_link() is now potentially oopsable. Look: suppose
> we've reached the link in RCU mode, just as it got unlinked. link->dentry
> has become negative and may_follow_link() steps into
> /* Allowed if owner and follower match. */
> inode = link->dentry->d_inode;
> if (uid_eq(current_cred()->fsuid, inode->i_uid))
> return 0;
> Oops... Incidentally, I suspect that your __read_seqcount_retry() in
> follow_link() might be lacking a barrier; why isn't full read_seqcount_retry()
> needed?
>
> FWIW, I would rather fetch ->d_inode *and* checked ->seq proir to calling
> get_link(), and passed inode to it as an explicit argument. And passed it
> to may_follow_link() as well...
Hrm... You know, something really weird is going on here. Where are
you setting nd->seq? I don't see anything in follow_link() doing that.
And nd->seq _definitely_ needs setting if you want to stay in RCU mode -
at that point it matches the dentry of symlink, not that of nd->path
(== parent directory). Neil, could you tell me which kernel you'd been
testing (ideally - commit ID is a public git tree), what config and what
tests had those been?
next prev parent reply other threads:[~2015-04-22 20:12 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-20 18:12 [RFC][PATCHSET] non-recursive link_path_walk() and reducing stack footprint Al Viro
2015-04-20 18:12 ` [PATCH 01/24] lustre: rip the private symlink nesting limit out Al Viro
2015-04-20 19:08 ` Andreas Dilger
2015-04-20 19:22 ` Al Viro
2015-04-20 20:35 ` Al Viro
2015-04-20 18:12 ` [PATCH 02/24] VFS: replace {, total_}link_count in task_struct with pointer to nameidata Al Viro
2015-04-20 18:12 ` [PATCH 03/24] ovl: rearrange ovl_follow_link to it doesn't need to call ->put_link Al Viro
2015-04-20 18:12 ` [PATCH 04/24] VFS: replace nameidata arg to ->put_link with a char* Al Viro
2015-04-20 18:12 ` [PATCH 05/24] SECURITY: remove nameidata arg from inode_follow_link Al Viro
2015-04-20 18:12 ` [PATCH 06/24] VFS: remove nameidata args from ->follow_link Al Viro
2015-04-20 18:12 ` [PATCH 07/24] namei: expand nested_symlink() in its only caller Al Viro
2015-04-20 18:12 ` [PATCH 08/24] namei.c: separate the parts of follow_link() that find the link body Al Viro
2015-04-20 18:12 ` [PATCH 09/24] namei: fold follow_link() into link_path_walk() Al Viro
2015-04-20 18:12 ` [PATCH 10/24] link_path_walk: handle get_link() returning ERR_PTR() immediately Al Viro
2015-04-20 18:12 ` [PATCH 11/24] link_path_walk: don't bother with walk_component() after jumping link Al Viro
2015-04-20 18:12 ` [PATCH 12/24] link_path_walk: turn inner loop into explicit goto Al Viro
2015-04-20 18:12 ` [PATCH 13/24] link_path_walk: massage a bit more Al Viro
2015-04-20 18:12 ` [PATCH 14/24] link_path_walk: get rid of duplication Al Viro
2015-04-20 18:12 ` [PATCH 15/24] link_path_walk: final preparations to killing recursion Al Viro
2015-04-20 18:13 ` [PATCH 16/24] link_path_walk: kill the recursion Al Viro
2015-04-20 21:04 ` Linus Torvalds
2015-04-20 21:32 ` Al Viro
2015-04-20 21:39 ` Linus Torvalds
2015-04-20 21:51 ` Al Viro
2015-04-20 21:41 ` Linus Torvalds
2015-04-20 21:42 ` Linus Torvalds
2015-04-20 21:59 ` Al Viro
2015-04-20 21:52 ` Al Viro
2015-04-20 18:13 ` [PATCH 17/24] link_path_walk: split "return from recursive call" path Al Viro
2015-04-20 18:13 ` [PATCH 18/24] link_path_walk: cleanup - turn goto start; into continue; Al Viro
2015-04-20 18:13 ` [PATCH 19/24] namei: fold may_follow_link() into follow_link() Al Viro
2015-04-20 18:13 ` [PATCH 20/24] namei: introduce nameidata->stack Al Viro
2015-04-20 18:13 ` [PATCH 21/24] namei: regularize use of put_link() and follow_link(), trim arguments Al Viro
2015-04-20 18:13 ` [PATCH 22/24] namei: trim the arguments of get_link() Al Viro
2015-04-20 18:13 ` [PATCH 23/24] new ->follow_link() and ->put_link() calling conventions Al Viro
2015-04-20 18:13 ` [PATCH 24/24] uninline walk_component() Al Viro
2015-04-21 14:49 ` [RFC][PATCHSET] non-recursive link_path_walk() and reducing stack footprint Al Viro
2015-04-21 15:04 ` Christoph Hellwig
2015-04-21 15:12 ` Richard Weinberger
2015-04-21 15:45 ` Al Viro
2015-04-21 16:46 ` Boaz Harrosh
2015-04-21 21:20 ` Al Viro
2015-04-22 18:07 ` Al Viro
2015-04-22 20:12 ` Al Viro [this message]
2015-04-22 21:05 ` Al Viro
2015-04-23 7:45 ` NeilBrown
2015-04-23 18:07 ` Al Viro
2015-04-24 6:35 ` NeilBrown
2015-04-24 13:42 ` Al Viro
2015-05-04 5:11 ` Al Viro
2015-05-04 7:30 ` NeilBrown
2015-04-23 5:01 ` Al Viro
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