Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> Ian Jackson  writes:
> > qemu_strtoul fails (returns an error) if the delimiter (that is, the
> > first character which is not processed as digit by strtoul) is not
> > '\0'.
> 
> It does that *only* when its @endptr argument is null.  Since you pass
> , it should work fine here.

I have just read it again and you are right.  Sorry.  I will fix this
then.

> > Does that all make sense ?
> 
> Your code makes sense to me.  It's just the comment that confuses me.
> Does ID mean "implementation-defined behavior"?  That would be wrong:

Yes, that's what I meant by ID.

>6.3.1.3  Signed and unsigned integers
> 
>[#1] When a value with integer type is converted to  another
>integer   type  other  than  _Bool,  if  the  value  can  be
>represented by the new type, it is unchanged.
> 
>[#2] Otherwise, if the new type is unsigned,  the  value  is
>converted  by repeatedly adding or subtracting one more than
>the maximum value that can be represented in  the  new  type
>until the value is in the range of the new type.

That applies if the new type (uid_t, here) is unsigned.  But I think
uid_t's signedness is not specified, so it might be signed.  (SuS
says, in the section on types.h, only

  Additionally:
 * nlink_t, uid_t, gid_t, and id_t shall be integer types.

C99 6.3.1.3 continues:

 Otherwise, the new type is signed and the value cannot be
 represented in it; either the result is
 implementation-defined or an implementation-defined signal is
 raised.

So the type of uid_t is ID too.

> One more thing: please report errors with error_report().  Here:

> error_report("Could not obtain uid");
> 
> No need to quote optarg back at the user, because error_report() already
> does.

Ah, I will do that.  Thanks.

Regards,
Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Markus Armbruster]

Ian Jackson  writes:

> Hi.  Thanks for the (re)-review.
>
> Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
> -runasid option"):
>> Ian Jackson  writes:
>> > +case QEMU_OPTION_runasid:
>> > +errno = 0;
>> > +lv = strtoul(optarg, , 0); /* can't qemu_strtoul, want 
>> > *ep=='.' */
>> 
>> I'm afraid I can't see why qemu_strtoul() wouldn't work here.  Can you
>> enlighten me?
>
> qemu_strtoul fails (returns an error) if the delimiter (that is, the
> first character which is not processed as digit by strtoul) is not
> '\0'.

It does that *only* when its @endptr argument is null.  Since you pass
, it should work fine here.

>Normally this is desirable, because it correctly rejects
> strings like "123blather".  But here we are trying to process a string
> whose first non-digit is ':', and we will handle the tail part
> explicitly.
>
> It would be possible to use strchr and then to write a '\0' over the
> ':' but I dislike that processing style (and it is forbidden by the
> const annotations on os_parse_cmd_args etc.)

I'd dislike that, too.

>> > +user_uid = lv; /* overflow here is ID in C99 */
>> 
>> I don't get the comment.  You check for overflow the obvious way below.
>> Sure you need a comment?
>
> This relates to overflow in the assignment, only.  lv is an unsigned
> long and user_uid is a uid_t (which may be smaller).  Normally, signed
> integer overflow is UB, but this is not the case when converting from
> another integer type.
>
> There are two possible overflows: 1. a string that strtoul cannot get
> to fit in an unsigned long, which produces a nonzero errno; and, 2. a
> value which fits in an unsigned long but not a uid_t.  In the latter
> case, we convert it _back_ into an unsigned long, as an implicit
> conversion in this middle test:
>
>> > +if (errno || *ep != '.' || user_uid != lv || user_uid == 
>> > (uid_t)-1) {
>
> If that succeeds, we know we can round-trip it so it is valid.  The
> remaining check needed is that it doesn't round trip to the sentinel
> uid value.
>
> Does that all make sense ?

Your code makes sense to me.  It's just the comment that confuses me.
Does ID mean "implementation-defined behavior"?  That would be wrong:

   6.3.1.3  Signed and unsigned integers

   [#1] When a value with integer type is converted to  another
   integer   type  other  than  _Bool,  if  the  value  can  be
   represented by the new type, it is unchanged.

   [#2] Otherwise, if the new type is unsigned,  the  value  is
   converted  by repeatedly adding or subtracting one more than
   the maximum value that can be represented in  the  new  type
   until the value is in the range of the new type.

> I'm not sure how much of this to document
> in comments.  It's deeply annoying that C is such a puzzle language
> here and that therefore such complicated reasoning and
> not-immediately-obvious code is needed, to do something so simple.
>
> If you would like me to remove the comment, I can drop it, of course.
> I don't really mind.

I'd drop it.

You might find this variation of your code slightly more obvious, or
slightly less:

if (errno || *ep != '.' || (uid_t)lv != lv || user_uid == (uid_t)-1) {
fprintf(stderr, "Could not obtain uid from \"%s\"", optarg);
exit(1);
}
user_uid = lv;

Your choice.

One more thing: please report errors with error_report().  Here:

error_report("Could not obtain uid");

No need to quote optarg back at the user, because error_report() already
does.

>> > +#ifndef _WIN32
>> > +DEF("runasid", HAS_ARG, QEMU_OPTION_runasid, \
>> > +"-runasid uid.gid change to numeric uid and gid just before 
>> > starting the VM\n",
>> > +QEMU_ARCH_ALL)
>> > +#endif
>> > +STEXI
>> > +@item -runasid @var{uid}.@var{gid}
>> 
>> Didn't we agree on using ':' instead of '.' as separator?
>> 
>> Sure we need yet another option?  Why can't we compatibly extend -runas?
>
> For some reason you are looking at an old version of the patch.  That
> may be my fault - there were a few mis-posts.  Sorry about that.

It could be just as well my fault: my inbox spun out of control before
KVM Forum.

> The final version does indeed have ':' and does reuse the -runas
> option.
>
>> If we truly need both, the rationale belongs into the commit message,
>> and we need to consider how they interact.  I'd recommend left-to-right
>> semantics, i.e. if you specify both, the last one wins.  Not what your
>> current code does, if I read it correctly.
>
> Happily this is now irrelevant.
>
> I will repost this series after I hear from you about strtoul and the
> overflow comment.

Thanks!

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

Hi.  Thanks for the (re)-review.

Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> Ian Jackson  writes:
> > +case QEMU_OPTION_runasid:
> > +errno = 0;
> > +lv = strtoul(optarg, , 0); /* can't qemu_strtoul, want *ep=='.' 
> > */
> 
> I'm afraid I can't see why qemu_strtoul() wouldn't work here.  Can you
> enlighten me?

qemu_strtoul fails (returns an error) if the delimiter (that is, the
first character which is not processed as digit by strtoul) is not
'\0'.  Normally this is desirable, because it correctly rejects
strings like "123blather".  But here we are trying to process a string
whose first non-digit is ':', and we will handle the tail part
explicitly.

It would be possible to use strchr and then to write a '\0' over the
':' but I dislike that processing style (and it is forbidden by the
const annotations on os_parse_cmd_args etc.)

> > +user_uid = lv; /* overflow here is ID in C99 */
> 
> I don't get the comment.  You check for overflow the obvious way below.
> Sure you need a comment?

This relates to overflow in the assignment, only.  lv is an unsigned
long and user_uid is a uid_t (which may be smaller).  Normally, signed
integer overflow is UB, but this is not the case when converting from
another integer type.

There are two possible overflows: 1. a string that strtoul cannot get
to fit in an unsigned long, which produces a nonzero errno; and, 2. a
value which fits in an unsigned long but not a uid_t.  In the latter
case, we convert it _back_ into an unsigned long, as an implicit
conversion in this middle test:

> > +if (errno || *ep != '.' || user_uid != lv || user_uid == 
> > (uid_t)-1) {

If that succeeds, we know we can round-trip it so it is valid.  The
remaining check needed is that it doesn't round trip to the sentinel
uid value.

Does that all make sense ?  I'm not sure how much of this to document
in comments.  It's deeply annoying that C is such a puzzle language
here and that therefore such complicated reasoning and
not-immediately-obvious code is needed, to do something so simple.

If you would like me to remove the comment, I can drop it, of course.
I don't really mind.

> > +#ifndef _WIN32
> > +DEF("runasid", HAS_ARG, QEMU_OPTION_runasid, \
> > +"-runasid uid.gid change to numeric uid and gid just before 
> > starting the VM\n",
> > +QEMU_ARCH_ALL)
> > +#endif
> > +STEXI
> > +@item -runasid @var{uid}.@var{gid}
> 
> Didn't we agree on using ':' instead of '.' as separator?
> 
> Sure we need yet another option?  Why can't we compatibly extend -runas?

For some reason you are looking at an old version of the patch.  That
may be my fault - there were a few mis-posts.  Sorry about that.

The final version does indeed have ':' and does reuse the -runas
option.

> If we truly need both, the rationale belongs into the commit message,
> and we need to consider how they interact.  I'd recommend left-to-right
> semantics, i.e. if you specify both, the last one wins.  Not what your
> current code does, if I read it correctly.

Happily this is now irrelevant.

I will repost this series after I hear from you about strtoul and the
overflow comment.

Regards,
Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Markus Armbruster]

Sorry for the slow response.

Ian Jackson  writes:

> This allows the caller to specify a uid and gid to use, even if there
> is no corresponding password entry.  This will be useful in certain
> Xen configurations.
>
> Signed-off-by: Ian Jackson 
> ---
> v3: Error messages fixed.  Thanks to Peter Maydell and Ross Lagerwall.
> v2: Coding style fixes.
> ---
>  os-posix.c  | 49 -
>  qemu-options.hx | 12 
>  2 files changed, 52 insertions(+), 9 deletions(-)
>
> diff --git a/os-posix.c b/os-posix.c
> index 92e9d85..6cc5868 100644
> --- a/os-posix.c
> +++ b/os-posix.c
> @@ -43,6 +43,8 @@
>  #endif
>  
>  static struct passwd *user_pwd;
> +static uid_t user_uid = (uid_t)-1;
> +static gid_t user_gid = (gid_t)-1;
>  static const char *chroot_dir;
>  static int daemonize;
>  static int daemon_pipe;
> @@ -134,6 +136,9 @@ void os_set_proc_name(const char *s)
>   */
>  void os_parse_cmd_args(int index, const char *optarg)
>  {
> +unsigned long lv;
> +char *ep;
> +int rc;
>  switch (index) {
>  #ifdef CONFIG_SLIRP
>  case QEMU_OPTION_smb:
> @@ -150,6 +155,22 @@ void os_parse_cmd_args(int index, const char *optarg)
>  exit(1);
>  }
>  break;
> +case QEMU_OPTION_runasid:
> +errno = 0;
> +lv = strtoul(optarg, , 0); /* can't qemu_strtoul, want *ep=='.' */

I'm afraid I can't see why qemu_strtoul() wouldn't work here.  Can you
enlighten me?

> +user_uid = lv; /* overflow here is ID in C99 */

I don't get the comment.  You check for overflow the obvious way below.
Sure you need a comment?

> +if (errno || *ep != '.' || user_uid != lv || user_uid == (uid_t)-1) {
> +fprintf(stderr, "Could not obtain uid from \"%s\"", optarg);
> +exit(1);
> +}
> +lv = 0;
> +rc = qemu_strtoul(ep + 1, 0, 0, );
> +user_gid = lv; /* overflow here is ID in C99 */

Likewise.

> +if (rc || user_gid != lv || user_gid == (gid_t)-1) {
> +fprintf(stderr, "Could not obtain gid from \"%s\"", optarg);
> +exit(1);
> +}
> +break;
>  case QEMU_OPTION_chroot:
>  chroot_dir = optarg;
>  break;
> @@ -166,18 +187,28 @@ void os_parse_cmd_args(int index, const char *optarg)
>  
>  static void change_process_uid(void)
>  {
> -if (user_pwd) {
> -if (setgid(user_pwd->pw_gid) < 0) {
> -fprintf(stderr, "Failed to setgid(%d)\n", user_pwd->pw_gid);
> +if (user_pwd || user_uid != (uid_t)-1) {
> +gid_t intended_gid = user_pwd ? user_pwd->pw_gid : user_gid;
> +uid_t intended_uid = user_pwd ? user_pwd->pw_uid : user_uid;
> +if (setgid(intended_gid) < 0) {
> +fprintf(stderr, "Failed to setgid(%d)\n", intended_gid);
>  exit(1);
>  }
> -if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
> -fprintf(stderr, "Failed to initgroups(\"%s\", %d)\n",
> -user_pwd->pw_name, user_pwd->pw_gid);
> -exit(1);
> +if (user_pwd) {
> +if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
> +fprintf(stderr, "Failed to initgroups(\"%s\", %d)\n",
> +user_pwd->pw_name, user_pwd->pw_gid);
> +exit(1);
> +}
> +} else {
> +if (setgroups(1, _gid) < 0) {
> +fprintf(stderr, "Failed to setgroups(1, [%d])",
> +user_gid);
> +exit(1);
> +}
>  }
> -if (setuid(user_pwd->pw_uid) < 0) {
> -fprintf(stderr, "Failed to setuid(%d)\n", user_pwd->pw_uid);
> +if (setuid(intended_uid) < 0) {
> +fprintf(stderr, "Failed to setuid(%d)\n", intended_uid);
>  exit(1);
>  }
>  if (setuid(0) != -1) {
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 9f6e2ad..34a5329 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -3968,6 +3968,18 @@ Immediately before starting guest execution, drop root 
> privileges, switching
>  to the specified user.
>  ETEXI
>  
> +#ifndef _WIN32
> +DEF("runasid", HAS_ARG, QEMU_OPTION_runasid, \
> +"-runasid uid.gid change to numeric uid and gid just before starting 
> the VM\n",
> +QEMU_ARCH_ALL)
> +#endif
> +STEXI
> +@item -runasid @var{uid}.@var{gid}

Didn't we agree on using ':' instead of '.' as separator?

Sure we need yet another option?  Why can't we compatibly extend -runas?

If we truly need both, the rationale belongs into the commit message,
and we need to consider how they interact.  I'd recommend left-to-right
semantics, i.e. if you specify both, the last one wins.  Not what your
current code does, if I read it correctly.

> +@findex -runasid
> +Immediately before starting guest execution, drop root privileges, switching
> +to the specified uid and 

Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> Actually, a numeric UID without group name or ID could be made to work
> just fine as long as it maps to a user name.  The use case may not be
> worth the bother, though.

In libxl's use case, it wouldn't map to a name.

> Using '.' to separate user and group is suboptimal, because POSIX
> portable user and group names may contain it:
...
> Coreutils uses ':'.  Let's follow its lead.

I'm happy to change it to use `:'.

Can you confirm that this command line interface is then OK ?
We would like to stablise the corresponding code in libxl...

Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> Actually, a numeric UID without group name or ID could be made to work
> just fine as long as it maps to a user name.  The use case may not be
> worth the bother, though.

In libxl's use case, it wouldn't map to a name.

> Using '.' to separate user and group is suboptimal, because POSIX
> portable user and group names may contain it:
...
> Coreutils uses ':'.  Let's follow its lead.

I'm happy to change it to use `:'.

Can you confirm that this command line interface is then OK ?
We would like to stablise the corresponding code in libxl...

Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Markus Armbruster]

Ian Jackson  writes:

> Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
> -runasid option"):
>> The last thing the QEMU command line needs is more exotic options.  Are
>> you sure we need a new one here?  Can we make existing -runas serve?
>> Precedence: Coreutils[*].  Pseudo-code:
>> 
>> if argument is a decimal number starting with '+':
>> user ID
>> else if argument is a valid user name:
>> user name
>> else if argument is a valid user ID:
>> user ID
>> else:
>> error
>
> I can do this.  So -runas . then.  I don't think it makes
> sense to try to -runas  because: you wouldn't have a username
> to pass to initgroups: not calling initgroups would be a bear trap;
> and otherwise we wouldn't know what gid to use.

Actually, a numeric UID without group name or ID could be made to work
just fine as long as it maps to a user name.  The use case may not be
worth the bother, though.

Using '.' to separate user and group is suboptimal, because POSIX
portable user and group names may contain it:

3.426 User Name

A string that is used to identify a user; see also User Database.
To be portable across systems conforming to IEEE Std 1003.1-2001,
the value is composed of characters from the portable filename
character set.  The hyphen should not be used as the first character
of a portable user name.

and

3.276 Portable Filename Character Set

The set of characters from which portable filenames are constructed.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t u v w x y z
0 1 2 3 4 5 6 7 8 9 . _ -

http://pubs.opengroup.org/onlinepubs/95399/basedefs/xbd_chap03.html

Coreutils uses ':'.  Let's follow its lead.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

(resending, more competently this time)

Daniel P. Berrange writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> Just use  getpwuid() to get the "struct passwd *", then change_process_uid()
> doesn't need any changes at all AFAICT.

See my comments in the commit message.  There may be multiple passwd
entries referring to a particular uid.  I think in this area it would
be better to expect the caller to be explicit, rather than taking
getpwuid's notion of the first one.

Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

Daniel P. Berrange writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> Just use  getpwuid() to get the "struct passwd *", then change_process_uid()
> doesn't need any changes at all AFAICT.

See my comments in the commit message.  There may be multiple passwd
entries referring to a particular uid.  I think in this area it would
be better to expect the caller to be explicit, rather than taking
getpwuid's notion of the first one.

Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Daniel P. Berrange]

On Mon, Oct 09, 2017 at 04:05:10PM +0100, Ian Jackson wrote:
> Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
> -runasid option"):
> > The last thing the QEMU command line needs is more exotic options.  Are
> > you sure we need a new one here?  Can we make existing -runas serve?
> > Precedence: Coreutils[*].  Pseudo-code:
> > 
> > if argument is a decimal number starting with '+':
> > user ID
> > else if argument is a valid user name:
> > user name
> > else if argument is a valid user ID:
> > user ID
> > else:
> > error
> 
> I can do this.  So -runas . then.  I don't think it makes
> sense to try to -runas  because: you wouldn't have a username
> to pass to initgroups: not calling initgroups would be a bear trap;
> and otherwise we wouldn't know what gid to use.

Just use  getpwuid() to get the "struct passwd *", then change_process_uid()
doesn't need any changes at all AFAICT.


Regards,
Daniel
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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

(resending to right address for xen-devel)

Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> The last thing the QEMU command line needs is more exotic options.  Are
> you sure we need a new one here?  Can we make existing -runas serve?
> Precedence: Coreutils[*].  Pseudo-code:
> 
> if argument is a decimal number starting with '+':
> user ID
> else if argument is a valid user name:
> user name
> else if argument is a valid user ID:
> user ID
> else:
> error

I can do this.  So -runas . then.  I don't think it makes
sense to try to -runas  because: you wouldn't have a username
to pass to initgroups: not calling initgroups would be a bear trap;
and otherwise we wouldn't know what gid to use.

Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

Markus Armbruster writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> The last thing the QEMU command line needs is more exotic options.  Are
> you sure we need a new one here?  Can we make existing -runas serve?
> Precedence: Coreutils[*].  Pseudo-code:
> 
> if argument is a decimal number starting with '+':
> user ID
> else if argument is a valid user name:
> user name
> else if argument is a valid user ID:
> user ID
> else:
> error

I can do this.  So -runas . then.  I don't think it makes
sense to try to -runas  because: you wouldn't have a username
to pass to initgroups: not calling initgroups would be a bear trap;
and otherwise we wouldn't know what gid to use.

Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Markus Armbruster]

Ian Jackson  writes:

> This allows the caller to specify a uid and gid to use, even if there
> is no corresponding password entry.  This will be useful in certain
> Xen configurations.
>
> Signed-off-by: Ian Jackson 
[...]
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 9f6e2ad..34a5329 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -3968,6 +3968,18 @@ Immediately before starting guest execution, drop root 
> privileges, switching
>  to the specified user.
>  ETEXI
>  
> +#ifndef _WIN32
> +DEF("runasid", HAS_ARG, QEMU_OPTION_runasid, \
> +"-runasid uid.gid change to numeric uid and gid just before starting 
> the VM\n",
> +QEMU_ARCH_ALL)
> +#endif
> +STEXI
> +@item -runasid @var{uid}.@var{gid}
> +@findex -runasid
> +Immediately before starting guest execution, drop root privileges, switching
> +to the specified uid and gid.
> +ETEXI
> +
>  DEF("prom-env", HAS_ARG, QEMU_OPTION_prom_env,
>  "-prom-env variable=value\n"
>  "set OpenBIOS nvram variables\n",

The last thing the QEMU command line needs is more exotic options.  Are
you sure we need a new one here?  Can we make existing -runas serve?
Precedence: Coreutils[*].  Pseudo-code:

if argument is a decimal number starting with '+':
user ID
else if argument is a valid user name:
user name
else if argument is a valid user ID:
user ID
else:
error

[*] 
https://www.gnu.org/software/coreutils/manual/html_node/Disambiguating-names-and-IDs.html

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

(resending to fix xen-devel CC)

Peter Maydell writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> On 4 October 2017 at 17:18, Ian Jackson  wrote:
> >  static void change_process_uid(void)
> >  {
> > -if (user_pwd) {
> > -if (setgid(user_pwd->pw_gid) < 0) {
> > +if (user_pwd || user_uid != (uid_t)-1) {
> > +if (setgid(user_pwd ? user_pwd->pw_gid : user_gid) < 0) {
> >  fprintf(stderr, "Failed to setgid(%d)\n", user_pwd->pw_gid);
> 
> If you're changing the gid we pass to setgid() I think you should
> also change the value we tell the user we tried to use in the
> error message, or it could be rather confusing.

Thanks for the review.  Sorry about the mess here.  I have fixed all
these problems.

Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Ian Jackson]

Peter Maydell writes ("Re: [Qemu-devel] [PATCH 7/8] os-posix: Provide new 
-runasid option"):
> On 4 October 2017 at 17:18, Ian Jackson  wrote:
> >  static void change_process_uid(void)
> >  {
> > -if (user_pwd) {
> > -if (setgid(user_pwd->pw_gid) < 0) {
> > +if (user_pwd || user_uid != (uid_t)-1) {
> > +if (setgid(user_pwd ? user_pwd->pw_gid : user_gid) < 0) {
> >  fprintf(stderr, "Failed to setgid(%d)\n", user_pwd->pw_gid);
> 
> If you're changing the gid we pass to setgid() I think you should
> also change the value we tell the user we tried to use in the
> error message, or it could be rather confusing.

Thanks for the review.  Sorry about the mess here.  I have fixed all
these problems.

Ian.

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Re: [Xen-devel] [Qemu-devel] [PATCH 7/8] os-posix: Provide new -runasid option

[Peter Maydell]

On 4 October 2017 at 17:18, Ian Jackson  wrote:
> This allows the caller to specify a uid and gid to use, even if there
> is no corresponding password entry.  This will be useful in certain
> Xen configurations.
>
> Signed-off-by: Ian Jackson 
> ---


> @@ -166,17 +187,19 @@ void os_parse_cmd_args(int index, const char *optarg)
>
>  static void change_process_uid(void)
>  {
> -if (user_pwd) {
> -if (setgid(user_pwd->pw_gid) < 0) {
> +if (user_pwd || user_uid != (uid_t)-1) {
> +if (setgid(user_pwd ? user_pwd->pw_gid : user_gid) < 0) {
>  fprintf(stderr, "Failed to setgid(%d)\n", user_pwd->pw_gid);

If you're changing the gid we pass to setgid() I think you should
also change the value we tell the user we tried to use in the
error message, or it could be rather confusing.

>  exit(1);
>  }
> -if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
> +if ((user_pwd
> + ? initgroups(user_pwd->pw_name, user_pwd->pw_gid)
> + : setgroups(1, _gid)) < 0) {
>  fprintf(stderr, "Failed to initgroups(\"%s\", %d)\n",
>  user_pwd->pw_name, user_pwd->pw_gid);

...and here we might claim we failed initgroups() when we actually
failed setgroups().

>  exit(1);
>  }
> -if (setuid(user_pwd->pw_uid) < 0) {
> +if (setuid(user_pwd ? user_pwd->pw_uid : user_gid) < 0) {
>  fprintf(stderr, "Failed to setuid(%d)\n", user_pwd->pw_uid);

This error message should be updated too.

thanks
-- PMM

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