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

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@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Will Deacon 2014-06-02 11:47:23 +01:00 committed by Catalin Marinas
parent 2d5a5612bc
commit c168870704
1 changed files with 4 additions and 0 deletions
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4
arch/arm64/kernel/ptrace.c
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@ -827,6 +827,7 @@ 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;
@ -834,10 +835,13 @@ 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;
}