waitid(2): leave copyout of siginfo to syscall itself

have kernel_waitid() collect the information needed for siginfo into
a small structure (waitid_info) passed to it; deal with copyout in
sys_waitid()/compat_sys_waitid().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 64 insertions, 104 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 94cdccf8e7e7..42f26480b3cc 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -996,12 +996,19 @@ SYSCALL_DEFINE1(exit_group, int, error_code)
         return 0;
 }
 
+struct waitid_info {
+        pid_t pid;
+        uid_t uid;
+        int status;
+        int cause;
+};
+
 struct wait_opts {
         enum pid_type           wo_type;
         int                     wo_flags;
         struct pid              *wo_pid;
 
-        struct siginfo __user   *wo_info;
+        struct waitid_info      *wo_info;
         int                     wo_stat;
         struct rusage           *wo_rusage;
 
@@ -1053,8 +1060,7 @@ eligible_child(struct wait_opts *wo, bool ptrace, struct task_struct *p)
 static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
                                 pid_t pid, uid_t uid, int why, int status)
 {
-        struct siginfo __user *infop;
-        int retval = 0;
+        struct waitid_info *infop;
 
         if (wo->wo_rusage)
                 getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
@@ -1062,22 +1068,12 @@ static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
         put_task_struct(p);
         infop = wo->wo_info;
         if (infop) {
-                if (!retval)
-                        retval = put_user(SIGCHLD, &infop->si_signo);
-                if (!retval)
-                        retval = put_user(0, &infop->si_errno);
-                if (!retval)
-                        retval = put_user((short)why, &infop->si_code);
-                if (!retval)
-                        retval = put_user(pid, &infop->si_pid);
-                if (!retval)
-                        retval = put_user(uid, &infop->si_uid);
-                if (!retval)
-                        retval = put_user(status, &infop->si_status);
+                infop->cause = why;
+                infop->pid = pid;
+                infop->uid = uid;
+                infop->status = status;
         }
-        if (!retval)
-                retval = pid;
-        return retval;
+        return pid;
 }
 
 /*
@@ -1088,10 +1084,10 @@ static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
  */
 static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
 {
-        int state, retval, status;
+        int state, status;
         pid_t pid = task_pid_vnr(p);
         uid_t uid = from_kuid_munged(current_user_ns(), task_uid(p));
-        struct siginfo __user *infop;
+        struct waitid_info *infop;
 
         if (!likely(wo->wo_flags & WEXITED))
                 return 0;
@@ -1186,36 +1182,22 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
 
         if (wo->wo_rusage)
                 getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
-        retval = 0;
         status = (p->signal->flags & SIGNAL_GROUP_EXIT)
                 ? p->signal->group_exit_code : p->exit_code;
         wo->wo_stat = status;
 
         infop = wo->wo_info;
-        if (!retval && infop)
-                retval = put_user(SIGCHLD, &infop->si_signo);
-        if (!retval && infop)
-                retval = put_user(0, &infop->si_errno);
-        if (!retval && infop) {
-                int why;
-
+        if (infop) {
                 if ((status & 0x7f) == 0) {
-                        why = CLD_EXITED;
-                        status >>= 8;
+                        infop->cause = CLD_EXITED;
+                        infop->status = status >> 8;
                 } else {
-                        why = (status & 0x80) ? CLD_DUMPED : CLD_KILLED;
-                        status &= 0x7f;
+                        infop->cause = (status & 0x80) ? CLD_DUMPED : CLD_KILLED;
+                        infop->status = status & 0x7f;
                 }
-                retval = put_user((short)why, &infop->si_code);
-                if (!retval)
-                        retval = put_user(status, &infop->si_status);
+                infop->pid = pid;
+                infop->uid = uid;
         }
-        if (!retval && infop)
-                retval = put_user(pid, &infop->si_pid);
-        if (!retval && infop)
-                retval = put_user(uid, &infop->si_uid);
-        if (!retval)
-                retval = pid;
 
         if (state == EXIT_TRACE) {
                 write_lock_irq(&tasklist_lock);
@@ -1232,7 +1214,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
         if (state == EXIT_DEAD)
                 release_task(p);
 
-        return retval;
+        return pid;
 }
 
 static int *task_stopped_code(struct task_struct *p, bool ptrace)
@@ -1268,8 +1250,8 @@ static int *task_stopped_code(struct task_struct *p, bool ptrace)
 static int wait_task_stopped(struct wait_opts *wo,
                                 int ptrace, struct task_struct *p)
 {
-        struct siginfo __user *infop;
-        int retval, exit_code, *p_code, why;
+        struct waitid_info *infop;
+        int exit_code, *p_code, why;
         uid_t uid = 0; /* unneeded, required by compiler */
         pid_t pid;
 
@@ -1320,28 +1302,19 @@ unlock_sig:
 
         if (wo->wo_rusage)
                 getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
-        retval = 0;
         wo->wo_stat = (exit_code << 8) | 0x7f;
 
         infop = wo->wo_info;
-        if (!retval && infop)
-                retval = put_user(SIGCHLD, &infop->si_signo);
-        if (!retval && infop)
-                retval = put_user(0, &infop->si_errno);
-        if (!retval && infop)
-                retval = put_user((short)why, &infop->si_code);
-        if (!retval && infop)
-                retval = put_user(exit_code, &infop->si_status);
-        if (!retval && infop)
-                retval = put_user(pid, &infop->si_pid);
-        if (!retval && infop)
-                retval = put_user(uid, &infop->si_uid);
-        if (!retval)
-                retval = pid;
+        if (infop) {
+                infop->cause = why;
+                infop->status = exit_code;
+                infop->pid = pid;
+                infop->uid = uid;
+        }
         put_task_struct(p);
 
-        BUG_ON(!retval);
-        return retval;
+        BUG_ON(!pid);
+        return pid;
 }
 
 /*
@@ -1618,7 +1591,7 @@ end:
         return retval;
 }
 
-static long kernel_waitid(int which, pid_t upid, struct siginfo __user *infop,
+static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
                           int options, struct rusage *ru)
 {
         struct wait_opts wo;
@@ -1660,27 +1633,8 @@ static long kernel_waitid(int which, pid_t upid, struct siginfo __user *infop,
         wo.wo_rusage    = ru;
         ret = do_wait(&wo);
 
-        if (ret > 0) {
+        if (ret > 0)
                 ret = 0;
-        } else if (infop) {
-                /*
-                 * For a WNOHANG return, clear out all the fields
-                 * we would set so the user can easily tell the
-                 * difference.
-                 */
-                if (!ret)
-                        ret = put_user(0, &infop->si_signo);
-                if (!ret)
-                        ret = put_user(0, &infop->si_errno);
-                if (!ret)
-                        ret = put_user(0, &infop->si_code);
-                if (!ret)
-                        ret = put_user(0, &infop->si_pid);
-                if (!ret)
-                        ret = put_user(0, &infop->si_uid);
-                if (!ret)
-                        ret = put_user(0, &infop->si_status);
-        }
 
         put_pid(pid);
         return ret;
@@ -1690,12 +1644,24 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
                 infop, int, options, struct rusage __user *, ru)
 {
         struct rusage r;
-        long err = kernel_waitid(which, upid, infop, options, ru ? &r : NULL);
+        struct waitid_info info = {.status = 0};
+        long err = kernel_waitid(which, upid, &info, options, ru ? &r : NULL);
 
         if (!err) {
                 if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
                         return -EFAULT;
         }
+        if (!infop)
+                return err;
+
+        if (put_user(err ? 0 : SIGCHLD, &infop->si_signo) ||
+            put_user(0, &infop->si_errno) ||
+            put_user((short)info.cause, &infop->si_code) ||
+            put_user(info.pid, &infop->si_pid) ||
+            put_user(info.uid, &infop->si_uid) ||
+            put_user(info.status, &infop->si_status))
+                err = -EFAULT;
+
         return err;
 }
 
@@ -1785,33 +1751,27 @@ COMPAT_SYSCALL_DEFINE5(waitid,
                 struct compat_siginfo __user *, infop, int, options,
                 struct compat_rusage __user *, uru)
 {
-        siginfo_t info;
         struct rusage ru;
-        long ret;
-        mm_segment_t old_fs = get_fs();
-
-        memset(&info, 0, sizeof(info));
+        struct waitid_info info = {.status = 0};
+        long err = kernel_waitid(which, pid, &info, options, uru ? &ru : NULL);
 
-        set_fs(KERNEL_DS);
-        ret = kernel_waitid(which, pid, (siginfo_t __user *)&info, options,
-                         uru ? &ru : NULL);
-        set_fs(old_fs);
-
-        if ((ret < 0) || (info.si_signo == 0))
-                return ret;
-
-        if (uru) {
-                /* sys_waitid() overwrites everything in ru */
+        if (!err && uru) {
+                /* kernel_waitid() overwrites everything in ru */
                 if (COMPAT_USE_64BIT_TIME)
-                        ret = copy_to_user(uru, &ru, sizeof(ru));
+                        err = copy_to_user(uru, &ru, sizeof(ru));
                 else
-                        ret = put_compat_rusage(&ru, uru);
-                if (ret)
+                        err = put_compat_rusage(&ru, uru);
+                if (err)
                         return -EFAULT;
         }
 
-        BUG_ON(info.si_code & __SI_MASK);
-        info.si_code |= __SI_CHLD;
-        return copy_siginfo_to_user32(infop, &info);
+        if (put_user(err ? 0 : SIGCHLD, &infop->si_signo) ||
+            put_user(0, &infop->si_errno) ||
+            put_user((short)info.cause, &infop->si_code) ||
+            put_user(info.pid, &infop->si_pid) ||
+            put_user(info.uid, &infop->si_uid) ||
+            put_user(info.status, &infop->si_status))
+                err = -EFAULT;
+        return err;
 }
 #endif