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Subject[REVIEW][PATCH 7/6] signal: In sigqueueinfo prefer sig not si_signo

Andrei Vagin <avagin@gmail.com> reported:

> Accoding to the man page, the user should not set si_signo, it has to be set
> by kernel.
>
> $ man 2 rt_sigqueueinfo
>
> The uinfo argument specifies the data to accompany the signal. This
> argument is a pointer to a structure of type siginfo_t, described in
> sigaction(2) (and defined by including <sigaction.h>). The caller
> should set the following fields in this structure:
>
> si_code
> This must be one of the SI_* codes in the Linux kernel source
> file include/asm-generic/siginfo.h, with the restriction that
> the code must be negative (i.e., cannot be SI_USER, which is
> used by the kernel to indicate a signal sent by kill(2)) and
> cannot (since Linux 2.6.39) be SI_TKILL (which is used by the
> kernel to indicate a signal sent using tgkill(2)).
>
> si_pid This should be set to a process ID, typically the process ID of
> the sender.
>
> si_uid This should be set to a user ID, typically the real user ID of
> the sender.
>
> si_value
> This field contains the user data to accompany the signal. For
> more information, see the description of the last (union sigval)
> argument of sigqueue(3).
>
> Internally, the kernel sets the si_signo field to the value specified
> in sig, so that the receiver of the signal can also obtain the signal
> number via that field.
>
> On Tue, Sep 25, 2018 at 07:19:02PM +0200, Eric W. Biederman wrote:
>>
>> If there is some application that calls sigqueueinfo directly that has
>> a problem with this added sanity check we can revisit this when we see
>> what kind of crazy that application is doing.
>
>
> I already know two "applications" ;)
>
> https://github.com/torvalds/linux/blob/master/tools/testing/selftests/ptrace/peeksiginfo.c
> https://github.com/checkpoint-restore/criu/blob/master/test/zdtm/static/sigpending.c
>
> Disclaimer: I'm the author of both of them.

Looking at the kernel code the historical behavior has alwasy been to prefer
the signal number passed in by the kernel.

So sigh. Implmenet __copy_siginfo_from_user and __copy_siginfo_from_user32 to
take that signal number and prefer it. The user of ptrace will still
use copy_siginfo_from_user and copy_siginfo_from_user32 as they do not and
never have had a signal number there.

Luckily this change has never made it farther than linux-next.

Fixes: e75dc036c445 ("signal: Fail sigqueueinfo if si_signo != sig")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---

Andrei can you verify this fixes your programs?
Thank you very much,
Eric


kernel/signal.c | 141 ++++++++++++++++++++++++++++--------------------
1 file changed, 84 insertions(+), 57 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 1c2dd117fee0..2bffc5a50183 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2925,11 +2925,10 @@ int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from)
return 0;
}

-int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from)
+static int post_copy_siginfo_from_user(kernel_siginfo_t *info,
+ const siginfo_t __user *from)
{
- if (copy_from_user(to, from, sizeof(struct kernel_siginfo)))
- return -EFAULT;
- if (unlikely(!known_siginfo_layout(to->si_signo, to->si_code))) {
+ if (unlikely(!known_siginfo_layout(info->si_signo, info->si_code))) {
char __user *expansion = si_expansion(from);
char buf[SI_EXPANSION_SIZE];
int i;
@@ -2949,6 +2948,22 @@ int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from)
return 0;
}

+static int __copy_siginfo_from_user(int signo, kernel_siginfo_t *to,
+ const siginfo_t __user *from)
+{
+ if (copy_from_user(to, from, sizeof(struct kernel_siginfo)))
+ return -EFAULT;
+ to->si_signo = signo;
+ return post_copy_siginfo_from_user(to, from);
+}
+
+int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from)
+{
+ if (copy_from_user(to, from, sizeof(struct kernel_siginfo)))
+ return -EFAULT;
+ return post_copy_siginfo_from_user(to, from);
+}
+
#ifdef CONFIG_COMPAT
int copy_siginfo_to_user32(struct compat_siginfo __user *to,
const struct kernel_siginfo *from)
@@ -3041,88 +3056,106 @@ int __copy_siginfo_to_user32(struct compat_siginfo __user *to,
return 0;
}

-int copy_siginfo_from_user32(struct kernel_siginfo *to,
- const struct compat_siginfo __user *ufrom)
+static int post_copy_siginfo_from_user32(kernel_siginfo_t *to,
+ const struct compat_siginfo *from)
{
- struct compat_siginfo from;
-
- if (copy_from_user(&from, ufrom, sizeof(struct compat_siginfo)))
- return -EFAULT;
-
clear_siginfo(to);
- to->si_signo = from.si_signo;
- to->si_errno = from.si_errno;
- to->si_code = from.si_code;
- switch(siginfo_layout(from.si_signo, from.si_code)) {
+ to->si_signo = from->si_signo;
+ to->si_errno = from->si_errno;
+ to->si_code = from->si_code;
+ switch(siginfo_layout(from->si_signo, from->si_code)) {
case SIL_KILL:
- to->si_pid = from.si_pid;
- to->si_uid = from.si_uid;
+ to->si_pid = from->si_pid;
+ to->si_uid = from->si_uid;
break;
case SIL_TIMER:
- to->si_tid = from.si_tid;
- to->si_overrun = from.si_overrun;
- to->si_int = from.si_int;
+ to->si_tid = from->si_tid;
+ to->si_overrun = from->si_overrun;
+ to->si_int = from->si_int;
break;
case SIL_POLL:
- to->si_band = from.si_band;
- to->si_fd = from.si_fd;
+ to->si_band = from->si_band;
+ to->si_fd = from->si_fd;
break;
case SIL_FAULT:
- to->si_addr = compat_ptr(from.si_addr);
+ to->si_addr = compat_ptr(from->si_addr);
#ifdef __ARCH_SI_TRAPNO
- to->si_trapno = from.si_trapno;
+ to->si_trapno = from->si_trapno;
#endif
break;
case SIL_FAULT_MCEERR:
- to->si_addr = compat_ptr(from.si_addr);
+ to->si_addr = compat_ptr(from->si_addr);
#ifdef __ARCH_SI_TRAPNO
- to->si_trapno = from.si_trapno;
+ to->si_trapno = from->si_trapno;
#endif
- to->si_addr_lsb = from.si_addr_lsb;
+ to->si_addr_lsb = from->si_addr_lsb;
break;
case SIL_FAULT_BNDERR:
- to->si_addr = compat_ptr(from.si_addr);
+ to->si_addr = compat_ptr(from->si_addr);
#ifdef __ARCH_SI_TRAPNO
- to->si_trapno = from.si_trapno;
+ to->si_trapno = from->si_trapno;
#endif
- to->si_lower = compat_ptr(from.si_lower);
- to->si_upper = compat_ptr(from.si_upper);
+ to->si_lower = compat_ptr(from->si_lower);
+ to->si_upper = compat_ptr(from->si_upper);
break;
case SIL_FAULT_PKUERR:
- to->si_addr = compat_ptr(from.si_addr);
+ to->si_addr = compat_ptr(from->si_addr);
#ifdef __ARCH_SI_TRAPNO
- to->si_trapno = from.si_trapno;
+ to->si_trapno = from->si_trapno;
#endif
- to->si_pkey = from.si_pkey;
+ to->si_pkey = from->si_pkey;
break;
case SIL_CHLD:
- to->si_pid = from.si_pid;
- to->si_uid = from.si_uid;
- to->si_status = from.si_status;
+ to->si_pid = from->si_pid;
+ to->si_uid = from->si_uid;
+ to->si_status = from->si_status;
#ifdef CONFIG_X86_X32_ABI
if (in_x32_syscall()) {
- to->si_utime = from._sifields._sigchld_x32._utime;
- to->si_stime = from._sifields._sigchld_x32._stime;
+ to->si_utime = from->_sifields._sigchld_x32._utime;
+ to->si_stime = from->_sifields._sigchld_x32._stime;
} else
#endif
{
- to->si_utime = from.si_utime;
- to->si_stime = from.si_stime;
+ to->si_utime = from->si_utime;
+ to->si_stime = from->si_stime;
}
break;
case SIL_RT:
- to->si_pid = from.si_pid;
- to->si_uid = from.si_uid;
- to->si_int = from.si_int;
+ to->si_pid = from->si_pid;
+ to->si_uid = from->si_uid;
+ to->si_int = from->si_int;
break;
case SIL_SYS:
- to->si_call_addr = compat_ptr(from.si_call_addr);
- to->si_syscall = from.si_syscall;
- to->si_arch = from.si_arch;
+ to->si_call_addr = compat_ptr(from->si_call_addr);
+ to->si_syscall = from->si_syscall;
+ to->si_arch = from->si_arch;
break;
}
return 0;
}
+
+static int __copy_siginfo_from_user32(int signo, struct kernel_siginfo *to,
+ const struct compat_siginfo __user *ufrom)
+{
+ struct compat_siginfo from;
+
+ if (copy_from_user(&from, ufrom, sizeof(struct compat_siginfo)))
+ return -EFAULT;
+
+ from.si_signo = signo;
+ return post_copy_siginfo_from_user32(to, &from);
+}
+
+int copy_siginfo_from_user32(struct kernel_siginfo *to,
+ const struct compat_siginfo __user *ufrom)
+{
+ struct compat_siginfo from;
+
+ if (copy_from_user(&from, ufrom, sizeof(struct compat_siginfo)))
+ return -EFAULT;
+
+ return post_copy_siginfo_from_user32(to, &from);
+}
#endif /* CONFIG_COMPAT */

/**
@@ -3359,9 +3392,6 @@ static int do_rt_sigqueueinfo(pid_t pid, int sig, kernel_siginfo_t *info)
(task_pid_vnr(current) != pid))
return -EPERM;

- if (info->si_signo != sig)
- return -EINVAL;
-
/* POSIX.1b doesn't mention process groups. */
return kill_proc_info(sig, info, pid);
}
@@ -3376,7 +3406,7 @@ SYSCALL_DEFINE3(rt_sigqueueinfo, pid_t, pid, int, sig,
siginfo_t __user *, uinfo)
{
kernel_siginfo_t info;
- int ret = copy_siginfo_from_user(&info, uinfo);
+ int ret = __copy_siginfo_from_user(sig, &info, uinfo);
if (unlikely(ret))
return ret;
return do_rt_sigqueueinfo(pid, sig, &info);
@@ -3389,7 +3419,7 @@ COMPAT_SYSCALL_DEFINE3(rt_sigqueueinfo,
struct compat_siginfo __user *, uinfo)
{
kernel_siginfo_t info;
- int ret = copy_siginfo_from_user32(&info, uinfo);
+ int ret = __copy_siginfo_from_user32(sig, &info, uinfo);
if (unlikely(ret))
return ret;
return do_rt_sigqueueinfo(pid, sig, &info);
@@ -3409,9 +3439,6 @@ static int do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, kernel_siginfo_t
(task_pid_vnr(current) != pid))
return -EPERM;

- if (info->si_signo != sig)
- return -EINVAL;
-
return do_send_specific(tgid, pid, sig, info);
}

@@ -3419,7 +3446,7 @@ SYSCALL_DEFINE4(rt_tgsigqueueinfo, pid_t, tgid, pid_t, pid, int, sig,
siginfo_t __user *, uinfo)
{
kernel_siginfo_t info;
- int ret = copy_siginfo_from_user(&info, uinfo);
+ int ret = __copy_siginfo_from_user(sig, &info, uinfo);
if (unlikely(ret))
return ret;
return do_rt_tgsigqueueinfo(tgid, pid, sig, &info);
@@ -3433,7 +3460,7 @@ COMPAT_SYSCALL_DEFINE4(rt_tgsigqueueinfo,
struct compat_siginfo __user *, uinfo)
{
kernel_siginfo_t info;
- int ret = copy_siginfo_from_user32(&info, uinfo);
+ int ret = __copy_siginfo_from_user32(sig, &info, uinfo);
if (unlikely(ret))
return ret;
return do_rt_tgsigqueueinfo(tgid, pid, sig, &info);
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