From: Eric W. Biederman ebiederm@xmission.com
commit f6e2aa91a46d2bc79fce9b93a988dbe7655c90c0 upstream.
Recently syzbot in conjunction with KMSAN reported that ptrace_peek_siginfo can copy an uninitialized siginfo to userspace. Inspecting ptrace_peek_siginfo confirms this.
The problem is that off when initialized from args.off can be initialized to a negaive value. At which point the "if (off >= 0)" test to see if off became negative fails because off started off negative.
Prevent the core problem by adding a variable found that is only true if a siginfo is found and copied to a temporary in preparation for being copied to userspace.
Prevent args.off from being truncated when being assigned to off by testing that off is <= the maximum possible value of off. Convert off to an unsigned long so that we should not have to truncate args.off, we have well defined overflow behavior so if we add another check we won't risk fighting undefined compiler behavior, and so that we have a type whose maximum value is easy to test for.
Cc: Andrei Vagin avagin@gmail.com Cc: stable@vger.kernel.org Reported-by: syzbot+0d602a1b0d8c95bdf299@syzkaller.appspotmail.com Fixes: 84c751bd4aeb ("ptrace: add ability to retrieve signals without removing from a queue (v4)") Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/ptrace.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
--- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -704,6 +704,10 @@ static int ptrace_peek_siginfo(struct ta if (arg.nr < 0) return -EINVAL;
+ /* Ensure arg.off fits in an unsigned long */ + if (arg.off > ULONG_MAX) + return 0; + if (arg.flags & PTRACE_PEEKSIGINFO_SHARED) pending = &child->signal->shared_pending; else @@ -711,18 +715,20 @@ static int ptrace_peek_siginfo(struct ta
for (i = 0; i < arg.nr; ) { kernel_siginfo_t info; - s32 off = arg.off + i; + unsigned long off = arg.off + i; + bool found = false;
spin_lock_irq(&child->sighand->siglock); list_for_each_entry(q, &pending->list, list) { if (!off--) { + found = true; copy_siginfo(&info, &q->info); break; } } spin_unlock_irq(&child->sighand->siglock);
- if (off >= 0) /* beyond the end of the list */ + if (!found) /* beyond the end of the list */ break;
#ifdef CONFIG_COMPAT