Re: [Qemu-devel] [PATCH RFC v3 1/7] Fix segmentation fault when qemu_signal_init fails

[Peter Xu]

On Wed, Sep 19, 2018 at 09:35:17PM +0800, Fei Li wrote:
> Currently, when qemu_signal_init() fails it only returns a non-zero
> value but without propagating any Error. But its callers need a
> non-null err when runs error_report_err(err), or else 0->msg occurs.
> 
> To avoid such segmentation fault, add a new Error parameter to make
> the call trace to propagate the err to the final caller.
> 
> This patch also adds the omitted error handling when creating signalfd
> pipe fails in qemu_signalfd_compat().
> 
> Signed-off-by: Fei Li <address@hidden>

Hi, Fei,

Please do s/comc/com/ in the CC list, then I can receive your
emails. :)

Could you explain a bit how the segfault is triggered?  malloc() and
pipe() aren't something that will fault easily to me, so I would think
we just assert (especially it's in a very early phase of the process).

Thanks,

> ---
>  include/qemu/osdep.h |  2 +-
>  util/compatfd.c      |  9 ++++++---
>  util/main-loop.c     | 11 +++++------
>  3 files changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index a91068df0e..09ed85fcb8 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -421,7 +421,7 @@ struct qemu_signalfd_siginfo {
>                               additional fields in the future) */
>  };
>  
> -int qemu_signalfd(const sigset_t *mask);
> +int qemu_signalfd(const sigset_t *mask, Error **errp);
>  void sigaction_invoke(struct sigaction *action,
>                        struct qemu_signalfd_siginfo *info);
>  #endif
> diff --git a/util/compatfd.c b/util/compatfd.c
> index 980bd33e52..d3ed890405 100644
> --- a/util/compatfd.c
> +++ b/util/compatfd.c
> @@ -16,6 +16,7 @@
>  #include "qemu/osdep.h"
>  #include "qemu-common.h"
>  #include "qemu/thread.h"
> +#include "qapi/error.h"
>  
>  #include <sys/syscall.h>
>  
> @@ -65,7 +66,7 @@ static void *sigwait_compat(void *opaque)
>      }
>  }
>  
> -static int qemu_signalfd_compat(const sigset_t *mask)
> +static int qemu_signalfd_compat(const sigset_t *mask, Error **errp)
>  {
>      struct sigfd_compat_info *info;
>      QemuThread thread;
> @@ -73,11 +74,13 @@ static int qemu_signalfd_compat(const sigset_t *mask)
>  
>      info = malloc(sizeof(*info));
>      if (info == NULL) {
> +        error_setg(errp, "Failed to allocate signalfd memory");
>          errno = ENOMEM;
>          return -1;
>      }
>  
>      if (pipe(fds) == -1) {
> +        error_setg(errp, "Failed to create signalfd pipe");
>          free(info);
>          return -1;
>      }
> @@ -94,7 +97,7 @@ static int qemu_signalfd_compat(const sigset_t *mask)
>      return fds[0];
>  }
>  
> -int qemu_signalfd(const sigset_t *mask)
> +int qemu_signalfd(const sigset_t *mask, Error **errp)
>  {
>  #if defined(CONFIG_SIGNALFD)
>      int ret;
> @@ -106,5 +109,5 @@ int qemu_signalfd(const sigset_t *mask)
>      }
>  #endif
>  
> -    return qemu_signalfd_compat(mask);
> +    return qemu_signalfd_compat(mask, errp);
>  }
> diff --git a/util/main-loop.c b/util/main-loop.c
> index affe0403c5..b783f3c806 100644
> --- a/util/main-loop.c
> +++ b/util/main-loop.c
> @@ -71,7 +71,7 @@ static void sigfd_handler(void *opaque)
>      }
>  }
>  
> -static int qemu_signal_init(void)
> +static int qemu_signal_init(Error **errp)
>  {
>      int sigfd;
>      sigset_t set;
> @@ -94,10 +94,9 @@ static int qemu_signal_init(void)
>      pthread_sigmask(SIG_BLOCK, &set, NULL);
>  
>      sigdelset(&set, SIG_IPI);
> -    sigfd = qemu_signalfd(&set);
> +    sigfd = qemu_signalfd(&set, errp);
>      if (sigfd == -1) {
> -        fprintf(stderr, "failed to create signalfd\n");
> -        return -errno;
> +        return -1;
>      }
>  
>      fcntl_setfl(sigfd, O_NONBLOCK);
> @@ -109,7 +108,7 @@ static int qemu_signal_init(void)
>  
>  #else /* _WIN32 */
>  
> -static int qemu_signal_init(void)
> +static int qemu_signal_init(Error **errp)
>  {
>      return 0;
>  }
> @@ -148,7 +147,7 @@ int qemu_init_main_loop(Error **errp)
>  
>      init_clocks(qemu_timer_notify_cb);
>  
> -    ret = qemu_signal_init();
> +    ret = qemu_signal_init(errp);
>      if (ret) {
>          return ret;
>      }
> -- 
> 2.13.7
> 
> 

Regards,

-- 
Peter Xu