Re: [Qemu-devel] [PATCH] linux-user: Add naive implementation of capget() syscall

[Blue Swirl]

On Wed, Sep 19, 2012 at 3:09 PM, Karol Lewandowski
<address@hidden> wrote:
> libcap, library used to manipulate posix file capabilities uses
> getcap() to query version of capabilities supported by running
> kernel. Information obtained from this syscall is then used to
> initialize data structures that can be used to set process
> or/and file capabilities.
>
> Providing capget() alone makes it possible to set posix file
> capabilities under qemu (using setcap(8)).
>
> Signed-off-by: Karol Lewandowski <address@hidden>
> ---
>  linux-user/syscall.c |   20 +++++++++++++++++++-
>  1 files changed, 19 insertions(+), 1 deletions(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 6257a04..bcd7a05 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -56,6 +56,7 @@ int __clone2(int (*fn)(void *), void *child_stack_base,
>  #include <utime.h>
>  #include <sys/sysinfo.h>
>  #include <sys/utsname.h>
> +#include <sys/capability.h>
>  //#include <sys/user.h>
>  #include <netinet/ip.h>
>  #include <netinet/tcp.h>
> @@ -97,6 +98,7 @@ int __clone2(int (*fn)(void *), void *child_stack_base,
>  #include <linux/fb.h>
>  #include <linux/vt.h>
>  #include <linux/dm-ioctl.h>
> +#include <linux/capability.h>
>  #include "linux_loop.h"
>  #include "cpu-uname.h"
>
> @@ -328,6 +330,11 @@ static int sys_getcwd1(char *buf, size_t size)
>    return strlen(buf)+1;
>  }
>
> +static int sys_capget(struct __user_cap_header_struct *hdr, struct 
> __user_cap_data_struct *data)
> +{
> +  return (capget(hdr, data));

This is not correct. The structure needs to be converted field by
field to host native format, especially endianness.

The parenthesis aren't useful.

> +}
> +
>  #ifdef CONFIG_ATFILE
>  /*
>   * Host system seems to have atfile syscall stubs available.  We
> @@ -7436,7 +7443,18 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          unlock_user(p, arg1, ret);
>          break;
>      case TARGET_NR_capget:
> -        goto unimplemented;
> +    {
> +       void *p2 = NULL;
> +       if (!(p = lock_user(VERIFY_WRITE, arg1, sizeof(struct 
> __user_cap_header_struct), 0)))
> +           goto efault;

Here and below you also assume that host structure size matches guest.

Missing braces, please read CODING_STYLE and use checkpatch.pl.

> +       if (arg2 && !(p2 = lock_user(VERIFY_WRITE, arg2, sizeof(struct 
> __user_cap_data_struct), 0)))
> +           goto efault;
> +       ret = get_errno(sys_capget(p, p2));
> +       unlock_user(p, arg1, sizeof(struct __user_cap_header_struct));
> +       if (arg2)
> +            unlock_user(p, arg2, sizeof(struct __user_cap_data_struct));
> +       break;
> +    }
>      case TARGET_NR_capset:
>          goto unimplemented;
>      case TARGET_NR_sigaltstack:
> --
> 1.7.5.4
>
>