sysctl: require CAP_SYS_RAWIO to set mmap_min_addr

Currently the mmap_min_addr value can only be bypassed during mmap when
the task has CAP_SYS_RAWIO.  However, the mmap_min_addr sysctl value itself
can be adjusted to 0 if euid == 0, allowing a bypass without CAP_SYS_RAWIO.
This patch adds a check for the capability before allowing mmap_min_addr to
be changed.

Signed-off-by: Kees Cook <kees.cook@canonical.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

diff --git a/security/min_addr.c b/security/min_addr.c
index c844eed..fc43c9d 100644 (file)
--- a/security/min_addr.c
+++ b/security/min_addr.c
@@ -33,6 +33,9 @@ int mmap_min_addr_handler(struct ctl_table *table, int write,
 {
        int ret;
 
+       if (!capable(CAP_SYS_RAWIO))
+               return -EPERM;
+
        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 
        update_mmap_min_addr();