On 09/19/2018 12:52 PM, Taras Kondratiuk wrote:
When files on NFSv4 server are not properly labeled (label doesn't match
a policy on a client) they will end up with unlabeled_t type which is
too generic. We would like to be able to set a default context per
mount. 'defcontext' mount option looks like a nice solution, but it
doesn't seem to be fully implemented for native labeling. Default
context is stored, but is never used.
The patch adds a fallback to a default context if a received context is
invalid. If the inode context is already initialized, then it is left
untouched to preserve a context set locally on a client.
Can you explain the use case further? Why are you exporting a
filesystem with security labeling enabled to a client that doesn't
understand all of the labels used within it? Why wouldn't you just
disable NFSv4 security labeling and/or use a regular context= mount to
assign a single context to all files in the mount?
To be clear, defcontext= doesn't work that way for local/FS_USE_XATTR
filesystems. The context specified by it is only used for:
1) files that don't implement the xattr inode operations at all,
2) files that lack a security.selinux xattr,
3) the MLS portion of the context if it was missing (strictly as a
legacy compatibility mechanism for RHEL4 which predated the enabling of
the MLS field/logic).
A file with a security.selinux xattr that is invalid under policy for
any reason other than a missing MLS field will be handled as having the
unlabeled context.
So this would be a divergence in semantics for defcontext= between
local/FS_USE_XATTR and NFS/FS_USE_NATIVE filesystems.
Signed-off-by: Taras Kondratiuk <takondra@xxxxxxxxx>
---
security/selinux/hooks.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ad9a9b8e9979..f7debe798bf5 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6598,7 +6598,30 @@ static void selinux_inode_invalidate_secctx(struct inode *inode)
*/
static int selinux_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen)
{
- return selinux_inode_setsecurity(inode, XATTR_SELINUX_SUFFIX, ctx, ctxlen, 0);
+ struct superblock_security_struct *sbsec;
+ struct inode_security_struct *isec;
+ int rc;
+
+ rc = selinux_inode_setsecurity(inode, XATTR_SELINUX_SUFFIX, ctx, ctxlen, 0);
In this case, we likely don't gain much by reusing
selinux_inode_setsecurity() here and could just inline the relevant
portion of it if we were to make this change. Logically they mean
different things.
+
+ /*
+ * In case of Native labeling with defcontext mount option fall back
+ * to a default SID if received context is invalid.
+ */
+ if (rc == -EINVAL) {
+ sbsec = inode->i_sb->s_security;
+ if (sbsec->behavior == SECURITY_FS_USE_NATIVE &&
+ sbsec->flags & DEFCONTEXT_MNT) {
+ isec = inode->i_security;
+ if (!isec->initialized) {
+ isec->sclass = inode_mode_to_security_class(inode->i_mode);
+ isec->sid = sbsec->def_sid;
+ isec->initialized = 1;
+ }
+ rc = 0;
+ }
+ }
+ return rc;
}
/*
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