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Date: Sat, 1 Aug 2020 11:20:44 -0400
From: Peilin Ye <yepeilin.cs@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Peilin Ye <yepeilin.cs@...il.com>,
"Dmitry V. Levin" <ldv@...linux.org>,
Elvira Khabirova <lineprinter@...linux.org>,
Dan Carpenter <dan.carpenter@...cle.com>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel-mentees@...ts.linuxfoundation.org,
linux-kernel@...r.kernel.org
Subject: [Linux-kernel-mentees] [PATCH v3] ptrace: Prevent kernel-infoleak in ptrace_get_syscall_info()
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@...r.kernel.org
Fixes: 201766a20e30 ("ptrace: add PTRACE_GET_SYSCALL_INFO request")
Suggested-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Peilin Ye <yepeilin.cs@...il.com>
---
Change in v3:
- Remove unnecessary `__aligned__` attribute. (Suggested by
Dmitry V. Levin <ldv@...linux.org>)
Change in v2:
- Add a padding field to `struct ptrace_syscall_info`, instead of
doing memset() on `info`. (Suggested by Dmitry V. Levin
<ldv@...linux.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; /* 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 */
/* last cacheline: 24 bytes */
};
$ _
include/uapi/linux/ptrace.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index a71b6e3b03eb..83ee45fa634b 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -81,7 +81,8 @@ struct seccomp_metadata {
struct ptrace_syscall_info {
__u8 op; /* PTRACE_SYSCALL_INFO_* */
- __u32 arch __attribute__((__aligned__(sizeof(__u32))));
+ __u8 pad[3];
+ __u32 arch;
__u64 instruction_pointer;
__u64 stack_pointer;
union {
--
2.25.1
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