[Qemu-devel] [PATCH] Avoid crash in epoll_ctl with EPOLL_CTL_DEL

[Giuseppe Musacchio <thatlemon@gmail.com>]

The `event` parameter is ignored by the kernel if `op` is EPOLL_CTL_DEL,
do the same and avoid returning EFAULT if garbage is passed instead of a
valid pointer.

Signed-off-by: Giuseppe Musacchio <thatlemon@gmail.com>
---
  linux-user/syscall.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 5e29e675e9..32d463d58d 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -11329,7 +11329,7 @@ static abi_long do_syscall1(void *cpu_env, int 
num, abi_long arg1,
      {
          struct epoll_event ep;
          struct epoll_event *epp = 0;
-        if (arg4) {
+        if (arg2 != EPOLL_CTL_DEL && arg4) {
              struct target_epoll_event *target_ep;
              if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
                  return -TARGET_EFAULT;
-- 
2.20.1