Date: Fri, 21 Oct 2011 18:53:33 +0200 From: "Christopher J. Ruwe" <cjr@cruwe.de> To: <freebsd-questions@freebsd.org> Subject: trying to learn systems programming, fear I have not understood and thus messed up Message-ID: <20111021185333.7c197a2a@dijkstra>
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To improve on my C and to learn something about systems programming, I
have begun to pick out "bite-size bits" from the bin-PRs. Currently, I
am dispairing about bin/149972, which is about 1) adding error handling
to pw being invoced "pw -u <username>" and 2) trying to get a uid from
the (incorrectly) passed username. Currently, I cannot accomplish want
I wanted to do, so I turn here for hints or help.
Three developers which I have failed to reach by mail (gpf@, kibab@,
bcr@) have added the necessary code
if ((arg =3D getarg(args, 'u')) !=3D NULL) {
if(isdigit((unsigned char)*arg->val)) {
pwd->pw_uid =3D (uid_t) atol(arg->val);
edited =3D 1;
if (pwd->pw_uid !=3D 0 && strcmp(pwd->pw_name, "root") =3D=3D 0)
errx(EX_DATAERR, "can't change uid of `root' account");
if (pwd->pw_uid =3D=3D 0 && strcmp(pwd->pw_name, "root") !=3D 0)
warnx("WARNING: account `%s' will have a uid of 0 (superuser
access!)", pwd->pw_name); } else {
/* Found something, but not a number */
/*
* XXX Shouldn't we try to map the passed string to the username?
* man page however says that we're expecting numeric uid...
*/
errx(EX_DATAERR, "Expected numeric user id as an argument to -u\n");
}
}
I have tried to follow the suggestion from the comment by modifiying
the else-statement thus:
} else {
struct passwd *trgpwd;
if (!(trgpwd =3D GETPWNAM(arg->val)))
errx(EX_DATAERR, "User %s does not exist", arg->val);
=20
if (strcmp(a_name->val,"root") =3D=3D 0)
errx(EX_DATAERR, "can't change uid of `root' account");
if (strcmp(trgpwd->pw_name, "root") =3D=3D 0)
warnx("WARNING: account `%s' will have a uid of 0 (superuser
access!)", pwd->pw_name);
pwd->pw_uid =3D (uid_t) (trgpwd->pw_uid); =20
edited =3D 1;
}=20
What happens is not what I intended. I invoke as "sudo ./pw usermod
testuser1 -u testuser2". I can get testuser2's pwd-entry by GETPWNAM
allright, but when I assign the pw_uid, so as to make testuser2's uid
the same as testuser1's and imgaining to retain all other values, ./pw
reports "pw: user 'testuser2' disappeared during update" and the
testuser2's /etc/passwd entry is replaced by testuser1's.
I fear I have not understood GETPWNAM correctly, as it seems to replace
the struct pwd as some sort of sideeffect. I could manually set all
pwd-members to the correct ones (those of testuser2), but I fear that I
have messed something up beforehand.
I am grateful for any suggestions and/or correction.=20
--=20
Christopher J. Ruwe
TZ GMT + 2
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