Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-5.2-pull-request' into staging

Fixes for epoll_ctl and stack_t

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* remotes/vivier2/tags/linux-user-for-5.2-pull-request:
  linux-user: Prevent crash in epoll_ctl
  linux-user: Correct definition of stack_t

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 17 insertions, 9 deletions

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 3160a9ba06..27adee908e 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -12590,17 +12590,25 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
         struct epoll_event ep;
         struct epoll_event *epp = 0;
         if (arg4) {
-            struct target_epoll_event *target_ep;
-            if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
-                return -TARGET_EFAULT;
+            if (arg2 != EPOLL_CTL_DEL) {
+                struct target_epoll_event *target_ep;
+                if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
+                    return -TARGET_EFAULT;
+                }
+                ep.events = tswap32(target_ep->events);
+                /*
+                 * The epoll_data_t union is just opaque data to the kernel,
+                 * so we transfer all 64 bits across and need not worry what
+                 * actual data type it is.
+                 */
+                ep.data.u64 = tswap64(target_ep->data.u64);
+                unlock_user_struct(target_ep, arg4, 0);
             }
-            ep.events = tswap32(target_ep->events);
-            /* The epoll_data_t union is just opaque data to the kernel,
-             * so we transfer all 64 bits across and need not worry what
-             * actual data type it is.
+            /*
+             * before kernel 2.6.9, EPOLL_CTL_DEL operation required a
+             * non-null pointer, even though this argument is ignored.
+             *
              */
-            ep.data.u64 = tswap64(target_ep->data.u64);
-            unlock_user_struct(target_ep, arg4, 0);
             epp = &ep;
         }
         return get_errno(epoll_ctl(arg1, arg2, arg3, epp));