Re: [Qemu-devel] [PATCH] linux-user, fix getgroups/getgroups32 when both args are zero.

[Kirill A. Shutemov]

On [Sat, 23.02.2008 12:00], Takashi Yoshii wrote:
> getgroups() and getgroups32() returns NGROUPS_MAX when both its two args are
> zero. But because we pass a ptr to allocated space as 2nd arg, this function
> are interfered. The patch attached fixed it.
> /yoshii
> ---
>     linux-user/syscall.c: fix getgroups{,32} when both args are zero.
> 

My version of patch to fix same problem:

    getgroups: return total number of supplementary group IDs for the
    process if size == 0

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index ad97871..96a11a9 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5029,6 +5029,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 
             grouplist = alloca(gidsetsize * sizeof(gid_t));
             ret = get_errno(getgroups(gidsetsize, grouplist));
+            if (gidsetsize == 0)
+                break;
             if (!is_error(ret)) {
                 target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 
2, 0);
                 if (!target_grouplist)
@@ -5179,6 +5181,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 
             grouplist = alloca(gidsetsize * sizeof(gid_t));
             ret = get_errno(getgroups(gidsetsize, grouplist));
+            if (gidsetsize == 0)
+                break;
             if (!is_error(ret)) {
                 target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 
4, 0);
                 if (!target_grouplist) {

Another patch for getgroups:

    Trivial optimization of getgroups syscall implementation:
    swap only returned groups, not all group in list.

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 6f2872f..ad97871 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5033,7 +5033,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                 target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 
2, 0);
                 if (!target_grouplist)
                     goto efault;
-                for(i = 0;i < gidsetsize; i++)
+                for(i = 0;i < ret; i++)
                     target_grouplist[i] = tswap16(grouplist[i]);
                 unlock_user(target_grouplist, arg2, gidsetsize * 2);
             }
@@ -5185,7 +5185,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                     ret = -TARGET_EFAULT;
                     goto fail;
                 }
-                for(i = 0;i < gidsetsize; i++)
+                for(i = 0;i < ret; i++)
                     target_grouplist[i] = tswap32(grouplist[i]);
                 unlock_user(target_grouplist, arg2, gidsetsize * 4);
             }

It makes getgroups much faster in some cases.

-- 
Regards,  Kirill A. Shutemov
 + Belarus, Minsk
 + Velesys Ltd, http://www.velesys.com/
 + ALT Linux Team, http://www.altlinux.com/

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