2010-07-14 06:18:47

by Kees Cook

Subject: [PATCH v2] Yama: verify inode is symlink to avoid bind mounts

The inode_follow_link LSM hook is called in bind mount situations as
well as for symlink situations, so we must explicitly check for the
inode being a symlink to not reject bind mounts in 1777 directories,
which seems to be a common NFSv4 configuration.

Signed-off-by: Kees Cook <[email protected]>
---
v2:
- actually set inode in time to use it. *face palm*
---
security/yama/yama_lsm.c | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 3b76386..51c6a3a 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -116,9 +116,13 @@ static int yama_inode_follow_link(struct dentry *dentry,
if (!protected_sticky_symlinks)
return 0;

+ /* if inode isn't a symlink, don't try to evaluate blocking it */
+ inode = dentry->d_inode;
+ if (!S_ISLNK(inode->i_mode))
+ return 0;
+
/* owner and follower match? */
cred = current_cred();
- inode = dentry->d_inode;
if (cred->fsuid == inode->i_uid)
return 0;

--
1.7.1


--
Kees Cook
Ubuntu Security Team

2010-07-20 23:01:28

by James Morris

Subject: Re: [PATCH v2] Yama: verify inode is symlink to avoid bind mounts

On Tue, 13 Jul 2010, Kees Cook wrote:

> The inode_follow_link LSM hook is called in bind mount situations as
> well as for symlink situations, so we must explicitly check for the
> inode being a symlink to not reject bind mounts in 1777 directories,
> which seems to be a common NFSv4 configuration.
>
> Signed-off-by: Kees Cook <[email protected]>
> ---
> v2:
> - actually set inode in time to use it. *face palm*

Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6#next


--
James Morris
<[email protected]>