[PATCH] binfmt_elf_fdpic: fix crash on MMU system with dynamic binaries

[Nicolas Pitre]

In elf_fdpic_map_file() there is a test to ensure the dynamic section in
user space is properly terminated. However it does so by dereferencing
a user address directly. Add proper user space accessor.

Signed-off-by: Nicolas Pitre <n...@linaro.org>
---
 fs/binfmt_elf_fdpic.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index cf93a4fad0..6ae00b1102 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -830,6 +830,9 @@ static int elf_fdpic_map_file(struct elf_fdpic_params 
*params,
                        if (phdr->p_vaddr >= seg->p_vaddr &&
                            phdr->p_vaddr + phdr->p_memsz <=
                            seg->p_vaddr + seg->p_memsz) {
+                               Elf32_Dyn __user *dyn;
+                               Elf32_Sword d_tag;
+
                                params->dynamic_addr =
                                        (phdr->p_vaddr - seg->p_vaddr) +
                                        seg->addr;
@@ -842,8 +845,9 @@ static int elf_fdpic_map_file(struct elf_fdpic_params 
*params,
                                        goto dynamic_error;
 
                                tmp = phdr->p_memsz / sizeof(Elf32_Dyn);
-                               if (((Elf32_Dyn *)
-                                    params->dynamic_addr)[tmp - 1].d_tag != 0)
+                               dyn = (Elf32_Dyn __user *)params->dynamic_addr;
+                               __get_user(d_tag, &dyn[tmp - 1].d_tag);
+                               if (d_tag != 0)
                                        goto dynamic_error;
                                break;
                        }