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src/login.c: Fix off-by-one buggs

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Before 3b7cc05387 ("lib: replace `USER_NAME_MAX_LENGTH` macro"), this
code did use a length.  It used a utmp(5) fixed-width buffer, so the
length matches the buffer size (there was no terminating NUL byte).
However, sysconf(_SC_LOGIN_NAME_MAX) returns a buffer size that accounts
for the terminating null byte; see sysconf(3).  Thus, the commit that
introduced the call to sysconf(3), should have taken that detail into
account.

403a2e3771 ("lib/chkname.c: Take NUL byte into account"), by Tobias,
caught that bug in <lib/chkname.c>, but missed that the same commit that
introduced that bug, introduced the same bug in two other places.
This fixes all remaining calls to sysconf(_SC_LOGIN_NAME_MAX).

I still observe some suspicious code after this fix:

	if (do_rlogin(hostname, username, max_size - 1, term, sizeof(term)))

	...

	login_prompt(username, max_size - 1);

We're passing size-1 to functions that want a size.  But since the fix
to those will be different, let's do that in the following commits.

Link: <https://github.com/shadow-maint/shadow/pull/935>
Link: <https://github.com/shadow-maint/shadow/issues/920#issuecomment-1926002209>
Link: <https://github.com/shadow-maint/shadow/pull/757>
Link: <https://github.com/shadow-maint/shadow/issues/674>
See-also: 403a2e3771 ("lib/chkname.c: Take NUL byte into account")
Fixes: 3b7cc05387 ("lib: replace `USER_NAME_MAX_LENGTH` macro")
Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>
Cc: Tobias Stoeckmann <tobias@stoeckmann.org>
Cc: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
This commit is contained in:
Alejandro Colomar
2024-02-05 13:14:13 +01:00
committed by Serge Hallyn
parent 714b6a53d5
commit 6551709e96
1 changed files with 11 additions and 8 deletions
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19
src/login.c
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@@ -572,11 +572,13 @@ int main (int argc, char **argv)
}
#ifdef RLOGIN
if (rflg) {
size_t max_size = sysconf(_SC_LOGIN_NAME_MAX);
size_t max_size = sysconf(_SC_LOGIN_NAME_MAX);
assert (NULL == username);
username = XMALLOC(max_size + 1, char);
username[max_size] = '\0';
if (do_rlogin (hostname, username, max_size, term, sizeof term)) {
username = XMALLOC(max_size, char);
username[max_size - 1] = '\0';
if (do_rlogin(hostname, username, max_size - 1, term, sizeof(term)))
{
preauth_flag = true;
} else {
free (username);
@@ -879,15 +881,16 @@ int main (int argc, char **argv)
failed = false; /* haven't failed authentication yet */
if (NULL == username) { /* need to get a login id */
size_t max_size = sysconf(_SC_LOGIN_NAME_MAX);
size_t max_size = sysconf(_SC_LOGIN_NAME_MAX);
if (subroot) {
closelog ();
exit (1);
}
preauth_flag = false;
username = XMALLOC(max_size + 1, char);
username[max_size] = '\0';
login_prompt (username, max_size);
username = XMALLOC(max_size, char);
username[max_size - 1] = '\0';
login_prompt(username, max_size - 1);
if ('\0' == username[0]) {
/* Prompt for a new login */