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From: NeilBrown <neilb@suse.de>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 02/20] STAGING/lustre: limit follow_link recursion using stack space.
Date: Mon, 23 Mar 2015 13:37:38 +1100
Message-ID: <20150323023738.8161.97062.stgit@notabene.brown> (raw)
In-Reply-To: <20150323023258.8161.32467.stgit@notabene.brown>

lustre's ->follow_link() uses a lot of stack space and so
need to limit symlink recursion based on stack size.

It currently tests current->link_count, but that will soon
become private to fs/namei.c.
So instead base on actual available stack space.
This patch aborts recursive symlinks in less than 2K of space
is available.  This seems consistent with current code, but
hasn't been tested.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 drivers/staging/lustre/lustre/llite/symlink.c |   21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/lustre/lustre/llite/symlink.c b/drivers/staging/lustre/lustre/llite/symlink.c
index 686b6a574cc5..ba37eb6b29dc 100644
--- a/drivers/staging/lustre/lustre/llite/symlink.c
+++ b/drivers/staging/lustre/lustre/llite/symlink.c
@@ -120,20 +120,27 @@ failed:
 
 static void *ll_follow_link(struct dentry *dentry, struct nameidata *nd)
 {
+	unsigned long avail_space;
 	struct inode *inode = dentry->d_inode;
 	struct ptlrpc_request *request = NULL;
 	int rc;
 	char *symname = NULL;
 
 	CDEBUG(D_VFSTRACE, "VFS Op\n");
-	/* Limit the recursive symlink depth to 5 instead of default
-	 * 8 links when kernel has 4k stack to prevent stack overflow.
-	 * For 8k stacks we need to limit it to 7 for local servers. */
-	if (THREAD_SIZE < 8192 && current->link_count >= 6) {
-		rc = -ELOOP;
-	} else if (THREAD_SIZE == 8192 && current->link_count >= 8) {
+	/* Limit the recursive symlink depth.
+	 * Previously limited to 5 instead of default 8 links when
+	 * kernel has 4k stack to prevent stack overflow.
+	 * For 8k stacks, was limited to 7 for local servers.
+	 * Now limited to ensure 2K of stack is available for lustre.
+	 */
+#ifdef CONFIG_STACK_GROWSUP
+	avail_space = end_of_stack(current) - &avail_space;
+#else
+	avail_space = &avail_space - end_of_stack(current);
+#endif
+	if (avail_space < 2048)
 		rc = -ELOOP;
-	} else {
+	else {
 		ll_inode_size_lock(inode);
 		rc = ll_readlink_internal(inode, &request, &symname);
 		ll_inode_size_unlock(inode);

  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-23  2:37 [PATCH 00/20] Support follow_link in RCU-walk - V3 NeilBrown
2015-03-23  2:37 ` NeilBrown [this message]
2015-04-18  3:01   ` [PATCH 02/20] STAGING/lustre: limit follow_link recursion using stack space Al Viro
2015-04-19 20:57     ` Andreas Dilger
2015-04-19 21:33       ` Al Viro
2015-04-20  2:29         ` Al Viro
2015-03-23  2:37 ` [PATCH 03/20] VFS: replace {, total_}link_count in task_struct with pointer to nameidata NeilBrown
2015-03-23  2:37 ` [PATCH 01/20] Documentation: remove outdated information from automount-support.txt NeilBrown
2015-03-23  2:37 ` [PATCH 10/20] security: make inode_follow_link RCU-walk aware NeilBrown
2015-03-23  2:37 ` [PATCH 04/20] ovl: rearrange ovl_follow_link to it doesn't need to call ->put_link NeilBrown
2015-03-23  2:37 ` [PATCH 07/20] VFS: remove nameidata args from ->follow_link NeilBrown
2015-03-23  2:37 ` [PATCH 06/20] SECURITY: remove nameidata arg from inode_follow_link NeilBrown
2015-03-23  2:37 ` [PATCH 05/20] VFS: replace nameidata arg to ->put_link with a char* NeilBrown
2015-03-23  2:37 ` [PATCH 09/20] security/selinux: pass 'flags' arg to avc_audit() and avc_has_perm_flags() NeilBrown
2015-03-23  2:37 ` [PATCH 11/20] VFS/namei: use terminate_walk when symlink lookup fails NeilBrown
2015-03-23  2:37 ` [PATCH 08/20] VFS: make all ->follow_link handlers aware for LOOKUP_RCU NeilBrown
2015-03-23  2:37 ` [PATCH 13/20] VFS/namei: abort RCU-walk on symlink if atime needs updating NeilBrown
2015-03-23  2:37 ` [PATCH 14/20] VFS/namei: add 'inode' arg to put_link() NeilBrown
2015-04-17 16:25   ` Al Viro
2015-04-17 19:09     ` Al Viro
2015-04-18  8:09       ` Al Viro
2015-03-23  2:37 ` [PATCH 16/20] VFS/namei: enable RCU-walk when following symlinks NeilBrown
2015-03-23  2:37 ` [PATCH 19/20] XFS: allow follow_link to often succeed in RCU-walk NeilBrown
2015-03-23  2:37 ` [PATCH 20/20] NFS: support LOOKUP_RCU in nfs_follow_link NeilBrown
2015-03-23  2:37 ` [PATCH 18/20] xfs: use RCU to free 'struct xfs_mount' NeilBrown
2015-03-23  2:37 ` [PATCH 17/20] VFS/namei: handle LOOKUP_RCU in page_follow_link_light NeilBrown
2015-03-23  2:37 ` [PATCH 12/20] VFS/namei: new flag to support RCU symlinks: LOOKUP_LINK_RCU NeilBrown
2015-03-23  2:37 ` [PATCH 15/20] VFS/namei: enhance follow_link to support RCU-walk NeilBrown
2015-03-25 23:23 ` [PATCH 00/20] Support follow_link in RCU-walk - V3 NeilBrown

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