[3.8.y.z extended stable] Patch "arm64: ptrace: change fs when passing kernel pointer to regset code" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Tue Jul 22 20:55:36 UTC 2014


This is a note to let you know that I have just added a patch titled

    arm64: ptrace: change fs when passing kernel pointer to regset code

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.27.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From bb5366f0cf69d4d577de81e92181c746559d186a Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon at arm.com>
Date: Mon, 2 Jun 2014 11:47:23 +0100
Subject: arm64: ptrace: change fs when passing kernel pointer to regset code

commit c168870704bcde6bb63d05f7882b620dd3985a46 upstream.

Our compat PTRACE_POKEUSR implementation simply passes the user data to
regset_copy_from_user after some simple range checking. Unfortunately,
the data in question has already been copied to the kernel stack by this
point, so the subsequent access_ok check fails and the ptrace request
returns -EFAULT. This causes problems tracing fork() with older versions
of strace.

This patch briefly changes the fs to KERNEL_DS, so that the access_ok
check passes even with a kernel address.

Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm64/kernel/ptrace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 5341534..8553668 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -872,6 +872,7 @@ static int compat_ptrace_write_user(struct task_struct *tsk, compat_ulong_t off,
 				    compat_ulong_t val)
 {
 	int ret;
+	mm_segment_t old_fs = get_fs();

 	if (off & 3 || off >= COMPAT_USER_SZ)
 		return -EIO;
@@ -879,10 +880,13 @@ static int compat_ptrace_write_user(struct task_struct *tsk, compat_ulong_t off,
 	if (off >= sizeof(compat_elf_gregset_t))
 		return 0;

+	set_fs(KERNEL_DS);
 	ret = copy_regset_from_user(tsk, &user_aarch32_view,
 				    REGSET_COMPAT_GPR, off,
 				    sizeof(compat_ulong_t),
 				    &val);
+	set_fs(old_fs);
+
 	return ret;
 }

--
1.9.1





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