* Re: [PATCH] ptrace: zero out siginfo_t in ptrace_peek_siginfo()
2018-09-26 15:17 [PATCH] ptrace: zero out siginfo_t in ptrace_peek_siginfo() Alexander Potapenko
@ 2018-10-10 7:16 ` Andrei Vagin
0 siblings, 0 replies; 2+ messages in thread
From: Andrei Vagin @ 2018-10-10 7:16 UTC (permalink / raw)
To: Alexander Potapenko; +Cc: oleg, linux-kernel, dvyukov, andreyknvl, w, avagin
On Wed, Sep 26, 2018 at 05:17:25PM +0200, Alexander Potapenko wrote:
> KMSAN reported the following infoleak:
>
> ==================================================================
> BUG: KMSAN: kernel-infoleak in _copy_to_user+0x15d/0x1f0
> ...
> Call Trace:
> __dump_stack lib/dump_stack.c:77
> dump_stack+0x2f5/0x430 lib/dump_stack.c:113
> kmsan_report+0x183/0x2b0 mm/kmsan/kmsan.c:917
> kmsan_internal_check_memory+0x17e/0x1f0 mm/kmsan/kmsan.c:981
> kmsan_copy_to_user+0x79/0xc0 mm/kmsan/kmsan_hooks.c:482
> _copy_to_user+0x15d/0x1f0 lib/usercopy.c:31
> copy_to_user ./include/linux/uaccess.h:183
> copy_siginfo_to_user+0x81/0x130 kernel/signal.c:2897
> ptrace_peek_siginfo kernel/ptrace.c:741
> ptrace_request+0x2278/0x2680 kernel/ptrace.c:912
> arch_ptrace+0xbdd/0x11a0 arch/x86/kernel/ptrace.c:877
> __do_sys_ptrace kernel/ptrace.c:1145
> __se_sys_ptrace+0x422/0x920 kernel/ptrace.c:1110
> __x64_sys_ptrace+0x56/0x70 kernel/ptrace.c:1110
> do_syscall_64+0xb8/0x100 arch/x86/entry/common.c:291
> entry_SYSCALL_64_after_hwframe+0x63/0xe7 arch/x86/entry/entry_64.S:240
> ...
> Local variable description: ----info.i@ptrace_request
> Variable was created at:
> ptrace_peek_siginfo kernel/ptrace.c:712
> ptrace_request+0xdf/0x2680 kernel/ptrace.c:912
> arch_ptrace+0xbdd/0x11a0 arch/x86/kernel/ptrace.c:877
>
> Bytes 16-127 of 128 are uninitialized
> Memory access starts at ffff88007af6fc90
> ==================================================================
>
> when calling ptrace(PTRACE_PEEKSIGINFO) for a traceable child process
> with args = {-1, 0, 1}.
>
> Initialize the |info| structure to avoid leaking stack data.
"info" is filled up by copy_siginfo(), which overwrites everything.
static inline void copy_siginfo(struct siginfo *to, const struct siginfo *from)
{
memcpy(to, from, sizeof(*to));
}
so here is another problem. We handle arg.off incorrectly. The right fix
should look something like this:
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 21fec73d45d4..e336434a6f71 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -710,7 +710,7 @@ static int ptrace_peek_siginfo(struct task_struct *child,
for (i = 0; i < arg.nr; ) {
siginfo_t info;
- s32 off = arg.off + i;
+ u64 off = arg.off + i;
spin_lock_irq(&child->sighand->siglock);
list_for_each_entry(q, &pending->list, list) {
@@ -721,7 +721,7 @@ static int ptrace_peek_siginfo(struct task_struct *child,
}
spin_unlock_irq(&child->sighand->siglock);
- if (off >= 0) /* beyond the end of the list */
+ if (off + 1 != 0) /* beyond the end of the list */
break;
#ifdef CONFIG_COMPAT
>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> Reported-by: syzbot+69c3bd9869b32e394c48@syzkaller.appspotmail.com
> Fixes: 84c751bd4aebb ("ptrace: add ability to retrieve signals without
> removing from a queue (v4)")
> Cc: Andrey Vagin <avagin@openvz.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Willy Tarreau <w@1wt.eu>
> ---
> kernel/ptrace.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 21fec73d45d4..92c3855c2b9c 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -712,6 +712,7 @@ static int ptrace_peek_siginfo(struct task_struct *child,
> siginfo_t info;
> s32 off = arg.off + i;
>
> + memset(&info, 0, sizeof(info));
> spin_lock_irq(&child->sighand->siglock);
> list_for_each_entry(q, &pending->list, list) {
> if (!off--) {
> --
> 2.19.0.605.g01d371f741-goog
>
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