Commit 15773ae938d8 ("signal/arc: Use force_sig_fault where
appropriate") adds undefined behaviour and kernel resource leak
to userspace in ARC do_page_fault() implementation.
This happens because we don't initialize si_code variable after we
switch to force_sig_fault using. si_code (as a part of siginfo_t
structure) was previously initialized by clear_siginfo(&info) call
which was removed.
Undefined behaviour path:
-------------------->8---------------------------
}}} a/arch/arc/mm/fault.c
!! -67,6 +67,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
struct task_struct *tsk = current;
struct mm_struct *mm = tsk->mm;
+ /// >>> si_code - uninitialized
int si_code;
int ret;
vm_fault_t fault;
int write = regs->ecr_cause & ECR_C_PROTV_STORE; /* ST/EX */
!! -81,8 +82,10 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
* only copy the information from the master page table,
* nothing more.
*/
+ /// >>> take true branch
if (address >= VMALLOC_START) {
ret = handle_kernel_vaddr_fault(address);
+ /// >>> take true branch
if (unlikely(ret))
+ /// >>> jump to label "bad_area_nosemaphore"
goto bad_area_nosemaphore;
else
!! -193,10 +196,13 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
bad_area:
up_read(&mm->mmap_sem);
+ /// >>> reach label "bad_area_nosemaphore"
bad_area_nosemaphore:
/* User mode accesses just cause a SIGSEGV */
+ /// >>> take true branch
if (user_mode(regs)) {
tsk->thread.fault_address = address;
+ /// >>> Ooops:
+ /// >>> use uninitialized value "si_code"
+ /// >>> when calling "force_sig_fault"
force_sig_fault(SIGSEGV, si_code, (void __user *)address, tsk);
return;
}
-------------------->8---------------------------
Fixes: 15773ae938d8 ("signal/arc: Use force_sig_fault where appropriate")
Signed-off-by: Eugeniy Paltsev <[email protected]>
---
arch/arc/mm/fault.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index c9da6102eb4f..e2d9fc3fea01 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -66,7 +66,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
struct vm_area_struct *vma = NULL;
struct task_struct *tsk = current;
struct mm_struct *mm = tsk->mm;
- int si_code;
+ int si_code = 0;
int ret;
vm_fault_t fault;
int write = regs->ecr_cause & ECR_C_PROTV_STORE; /* ST/EX */
--
2.14.5
On 11/7/18 4:12 AM, Eugeniy Paltsev wrote:
> Commit 15773ae938d8 ("signal/arc: Use force_sig_fault where
> appropriate") adds undefined behaviour and kernel resource leak
> to userspace in ARC do_page_fault() implementation.
>
> This happens because we don't initialize si_code variable after we
> switch to force_sig_fault using. si_code (as a part of siginfo_t
> structure) was previously initialized by clear_siginfo(&info) call
> which was removed.
>
> Undefined behaviour path:
> -------------------->8---------------------------
> }}} a/arch/arc/mm/fault.c
> !! -67,6 +67,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
> struct task_struct *tsk = current;
> struct mm_struct *mm = tsk->mm;
> + /// >>> si_code - uninitialized
> int si_code;
> int ret;
> vm_fault_t fault;
> int write = regs->ecr_cause & ECR_C_PROTV_STORE; /* ST/EX */
> !! -81,8 +82,10 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
> * only copy the information from the master page table,
> * nothing more.
> */
> + /// >>> take true branch
> if (address >= VMALLOC_START) {
> ret = handle_kernel_vaddr_fault(address);
> + /// >>> take true branch
> if (unlikely(ret))
While the fix is legit, are you sure this code path was taken. VMALLOC_START is
memory for kernel modules and/or vmalloc. So the fault was induced in kernel space
in which case user_mode)r) will not be true.
> + /// >>> jump to label "bad_area_nosemaphore"
> goto bad_area_nosemaphore;
> else
> !! -193,10 +196,13 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
> bad_area:
> up_read(&mm->mmap_sem);
>
> + /// >>> reach label "bad_area_nosemaphore"
> bad_area_nosemaphore:
> /* User mode accesses just cause a SIGSEGV */
> + /// >>> take true branch
> if (user_mode(regs)) {
> tsk->thread.fault_address = address;
> + /// >>> Ooops:
> + /// >>> use uninitialized value "si_code"
> + /// >>> when calling "force_sig_fault"
> force_sig_fault(SIGSEGV, si_code, (void __user *)address, tsk);
> return;
> }
> -------------------->8---------------------------
>
> Fixes: 15773ae938d8 ("signal/arc: Use force_sig_fault where appropriate")
> Signed-off-by: Eugeniy Paltsev <[email protected]>
Added to for-curr after trimming the changelog
Thx,
-Vineet