From: Serge E. Hallyn <serue@xxxxxxxxxx>
Granting userid capabilities to another task is a dangerous
privilege. Don't just let file permissions authorize it.
Define CAP_GRANT_ID as a new capability needed to write to
/dev/caphash.
For one thing this lets us start a factotum server early on
in init, then have init drop CAP_GRANT_ID from its bounding
set so the rest of the system cannot regain it.
Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx>
Cc: Greg KH <greg@xxxxxxxxx>
cc: rsc@xxxxxxxxx
Cc: Ashwin Ganti <ashwin.ganti@xxxxxxxxx>
Cc: ericvh@xxxxxxxxx
Cc: devel@xxxxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Ron Minnich <rminnich@xxxxxxxxx>
---
drivers/staging/p9auth/p9auth.c | 4 ++++
include/linux/capability.h | 6 +++++-
2 files changed, 9 insertions(+), 1 deletions(-)
diff --git a/drivers/staging/p9auth/p9auth.c b/drivers/staging/p9auth/p9auth.c
index 8f70daa..fb27459 100644
--- a/drivers/staging/p9auth/p9auth.c
+++ b/drivers/staging/p9auth/p9auth.c
@@ -201,6 +201,10 @@ static ssize_t cap_write(struct file *filp, const char __user *buf,
retval = -EINVAL;
goto out;
}
+ if (!capable(CAP_GRANT_ID)) {
+ retval = -EPERM;
+ goto out;
+ }
printk(KERN_INFO "Capability being written to /dev/caphash : \n");
hexdump(user_buf, count);
memcpy(node_ptr->data, user_buf, count);
diff --git a/include/linux/capability.h b/include/linux/capability.h
index 39e5ff5..ba2cbfe 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -355,7 +355,11 @@ struct cpu_vfs_cap_data {
#define CAP_MAC_ADMIN 33
-#define CAP_LAST_CAP CAP_MAC_ADMIN
+/* Allow granting setuid capabilities through p9auth /dev/caphash */
+
+#define CAP_GRANT_ID 34
+
+#define CAP_LAST_CAP CAP_GRANT_ID
#define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
--
1.6.1
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