frv: fix address verification holes in setup_frame/setup_rt_frame

a) sa_handler might be maliciously set to point to kernel memory;
   blindly dereferencing it in FDPIC case is a Bad Idea(tm).

b) I'm not sure you need that set_fs(USER_DS) there at all, but if you
   do, you'd better do it *before* checking the frame you've decided to
   use with access_ok(), lest sigaltstack() becomes a convenient
   roothole.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 22 insertions, 16 deletions

diff --git a/arch/frv/kernel/signal.c b/arch/frv/kernel/signal.c
index 7fc29615ef01..5fb2d0661c78 100644
--- a/arch/frv/kernel/signal.c
+++ b/arch/frv/kernel/signal.c
@@ -253,6 +253,8 @@ static int setup_frame(int sig, struct k_sigaction *ka, sigset_t *set)
         struct sigframe __user *frame;
         int rsig;
 
+        set_fs(USER_DS);
+
         frame = get_sigframe(ka, sizeof(*frame));
 
         if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
@@ -296,22 +298,23 @@ static int setup_frame(int sig, struct k_sigaction *ka, sigset_t *set)
                                    (unsigned long) (frame->retcode + 2));
         }
 
-        /* set up registers for signal handler */
-        __frame->sp   = (unsigned long) frame;
-        __frame->lr   = (unsigned long) &frame->retcode;
-        __frame->gr8  = sig;
-
+        /* Set up registers for the signal handler */
         if (current->personality & FDPIC_FUNCPTRS) {
                 struct fdpic_func_descriptor __user *funcptr =
                         (struct fdpic_func_descriptor __user *) ka->sa.sa_handler;
-                __get_user(__frame->pc, &funcptr->text);
-                __get_user(__frame->gr15, &funcptr->GOT);
+                struct fdpic_func_descriptor desc;
+                if (copy_from_user(&desc, funcptr, sizeof(desc)))
+                        goto give_sigsegv;
+                __frame->pc = desc.text;
+                __frame->gr15 = desc.GOT;
         } else {
                 __frame->pc   = (unsigned long) ka->sa.sa_handler;
                 __frame->gr15 = 0;
         }
 
-        set_fs(USER_DS);
+        __frame->sp   = (unsigned long) frame;
+        __frame->lr   = (unsigned long) &frame->retcode;
+        __frame->gr8  = sig;
 
         /* the tracer may want to single-step inside the handler */
         if (test_thread_flag(TIF_SINGLESTEP))
@@ -341,6 +344,8 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
         struct rt_sigframe __user *frame;
         int rsig;
 
+        set_fs(USER_DS);
+
         frame = get_sigframe(ka, sizeof(*frame));
 
         if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
@@ -395,22 +400,23 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
         }
 
         /* Set up registers for signal handler */
-        __frame->sp  = (unsigned long) frame;
-        __frame->lr   = (unsigned long) &frame->retcode;
-        __frame->gr8 = sig;
-        __frame->gr9 = (unsigned long) &frame->info;
-
         if (current->personality & FDPIC_FUNCPTRS) {
                 struct fdpic_func_descriptor __user *funcptr =
                         (struct fdpic_func_descriptor __user *) ka->sa.sa_handler;
-                __get_user(__frame->pc, &funcptr->text);
-                __get_user(__frame->gr15, &funcptr->GOT);
+                struct fdpic_func_descriptor desc;
+                if (copy_from_user(&desc, funcptr, sizeof(desc)))
+                        goto give_sigsegv;
+                __frame->pc = desc.text;
+                __frame->gr15 = desc.GOT;
         } else {
                 __frame->pc   = (unsigned long) ka->sa.sa_handler;
                 __frame->gr15 = 0;
         }
 
-        set_fs(USER_DS);
+        __frame->sp  = (unsigned long) frame;
+        __frame->lr  = (unsigned long) &frame->retcode;
+        __frame->gr8 = sig;
+        __frame->gr9 = (unsigned long) &frame->info;
 
         /* the tracer may want to single-step inside the handler */
         if (test_thread_flag(TIF_SINGLESTEP))