nfsd: nfsd should drop CAP_MKNOD for non-root

Since creating a device node is normally an operation requiring special
privilege, Igor Zhbanov points out that it is surprising (to say the
least) that a client can, for example, create a device node on a
filesystem exported with root_squash.

So, make sure CAP_MKNOD is among the capabilities dropped when an nfsd
thread handles a request from a non-root user.

Reported-by: Igor Zhbanov <izh1979@gmail.com>
Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 1b9872556131..4864a43b2b45 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -393,8 +393,10 @@ struct cpu_vfs_cap_data {
 # define CAP_FULL_SET     ((kernel_cap_t){{ ~0, ~0 }})
 # define CAP_INIT_EFF_SET ((kernel_cap_t){{ ~CAP_TO_MASK(CAP_SETPCAP), ~0 }})
 # define CAP_FS_SET       ((kernel_cap_t){{ CAP_FS_MASK_B0, CAP_FS_MASK_B1 } })
-# define CAP_NFSD_SET     ((kernel_cap_t){{ CAP_FS_MASK_B0|CAP_TO_MASK(CAP_SYS_RESOURCE), \
-                                        CAP_FS_MASK_B1 } })
+# define CAP_NFSD_SET     ((kernel_cap_t){{ CAP_FS_MASK_B0 \
+                                            | CAP_TO_MASK(CAP_SYS_RESOURCE) \
+                                            | CAP_TO_MASK(CAP_MKNOD), \
+                                            CAP_FS_MASK_B1 } })
 
 #endif /* _KERNEL_CAPABILITY_U32S != 2 */