Messages in this thread Patch in this message | | | From | Kamal Mostafa <> | Subject | [PATCH 3.8 088/116] arm64: ptrace: change fs when passing kernel pointer to regset code | Date | Tue, 22 Jul 2014 15:21:39 -0700 |
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3.8.13.27 -stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon <will.deacon@arm.com>
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@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Kamal Mostafa <kamal@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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