Messages in this thread | | | Date | Sat, 1 Aug 2020 14:06:46 +0300 | From | "Dmitry V. Levin" <> | Subject | Re: [Linux-kernel-mentees] [PATCH v2] ptrace: Prevent kernel-infoleak in ptrace_get_syscall_info() |
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On Fri, Jul 31, 2020 at 10:08:41PM -0400, Peilin Ye wrote: > ptrace_get_syscall_info() is potentially copying uninitialized stack > memory to userspace, since the compiler may leave a 3-byte hole near the > beginning of `info`. Fix it by adding a padding field to `struct > ptrace_syscall_info`. > > Cc: stable@vger.kernel.org > Fixes: 201766a20e30 ("ptrace: add PTRACE_GET_SYSCALL_INFO request") > Suggested-by: Dan Carpenter <dan.carpenter@oracle.com> > Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com> > --- > Change in v2: > - Add a padding field to `struct ptrace_syscall_info`, instead of > doing memset() on `info`. (Suggested by Dmitry V. Levin > <ldv@altlinux.org>) > > Reference: https://lwn.net/Articles/417989/ > > $ # before: > $ pahole -C "ptrace_syscall_info" kernel/ptrace.o > struct ptrace_syscall_info { > __u8 op; /* 0 1 */ > > /* XXX 3 bytes hole, try to pack */ > > __u32 arch __attribute__((__aligned__(4))); /* 4 4 */ > __u64 instruction_pointer; /* 8 8 */ > __u64 stack_pointer; /* 16 8 */ > union { > struct { > __u64 nr; /* 24 8 */ > __u64 args[6]; /* 32 48 */ > } entry; /* 24 56 */ > struct { > __s64 rval; /* 24 8 */ > __u8 is_error; /* 32 1 */ > } exit; /* 24 16 */ > struct { > __u64 nr; /* 24 8 */ > __u64 args[6]; /* 32 48 */ > /* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */ > __u32 ret_data; /* 80 4 */ > } seccomp; /* 24 64 */ > }; /* 24 64 */ > > /* size: 88, cachelines: 2, members: 5 */ > /* sum members: 85, holes: 1, sum holes: 3 */ > /* forced alignments: 1, forced holes: 1, sum forced holes: 3 */ > /* last cacheline: 24 bytes */ > } __attribute__((__aligned__(8))); > $ > $ # after: > $ pahole -C "ptrace_syscall_info" kernel/ptrace.o > struct ptrace_syscall_info { > __u8 op; /* 0 1 */ > __u8 pad[3]; /* 1 3 */ > __u32 arch __attribute__((__aligned__(4))); /* 4 4 */ > __u64 instruction_pointer; /* 8 8 */ > __u64 stack_pointer; /* 16 8 */ > union { > struct { > __u64 nr; /* 24 8 */ > __u64 args[6]; /* 32 48 */ > } entry; /* 24 56 */ > struct { > __s64 rval; /* 24 8 */ > __u8 is_error; /* 32 1 */ > } exit; /* 24 16 */ > struct { > __u64 nr; /* 24 8 */ > __u64 args[6]; /* 32 48 */ > /* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */ > __u32 ret_data; /* 80 4 */ > } seccomp; /* 24 64 */ > }; /* 24 64 */ > > /* size: 88, cachelines: 2, members: 6 */ > /* forced alignments: 1 */ > /* last cacheline: 24 bytes */ > } __attribute__((__aligned__(8))); > $ _ > > include/uapi/linux/ptrace.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h > index a71b6e3b03eb..a518ba514bac 100644 > --- a/include/uapi/linux/ptrace.h > +++ b/include/uapi/linux/ptrace.h > @@ -81,6 +81,7 @@ struct seccomp_metadata { > > struct ptrace_syscall_info { > __u8 op; /* PTRACE_SYSCALL_INFO_* */ > + __u8 pad[3]; > __u32 arch __attribute__((__aligned__(sizeof(__u32)))); > __u64 instruction_pointer; > __u64 stack_pointer;
Funnily enough, but in first editions of PTRACE_GET_SYSCALL_INFO patchset [1] this was looking very similar:
+struct ptrace_syscall_info { + __u8 op; /* PTRACE_SYSCALL_INFO_* */ + __u8 __pad0[3]; + __u32 arch;
But later we decided [2][3] to replace the pad with a hole.
Note that the sole purpose of the __aligned__ attribute on the field that follows the hole is to guarantee that the hole has the same size across architectures. As this hole is being replaced back with a pad, that __aligned__ attribute is no longer needed and can be omitted along with adding the pad.
[1] https://lore.kernel.org/linux-api/20181125022150.46258a20@akathisia/ [2] https://lore.kernel.org/linux-api/20181211162305.GA480@altlinux.org/ [3] https://lore.kernel.org/linux-api/20181213171833.GA5240@altlinux.org/
-- ldv
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