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Subject[PATCH] binfmt_elf_fdpic: fix crash on MMU system with dynamic binaries
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 <nico@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;
}
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