From: Petr Lautrbach <plautrba@redhat.com>
To: selinux@vger.kernel.org
Cc: Petr Lautrbach <plautrba@redhat.com>,
Nicolas Iooss <nicolas.iooss@m4x.org>
Subject: Re: [PATCH] libsemanage: genhomedircon - improve handling large groups
Date: Fri, 08 Feb 2019 17:46:15 +0100 [thread overview]
Message-ID: <pjdimxuxm7c.fsf@redhat.com> (raw)
In-Reply-To: <CAJfZ7=nBvZHQ6Uq4GXK=0mxf1iBt8TQEVCkOZd4mNoW4OV7NSg@mail.gmail.com>
Nicolas Iooss <nicolas.iooss@m4x.org> writes:
> On Wed, Feb 6, 2019 at 8:45 PM Petr Lautrbach
> <plautrba@redhat.com> wrote:
>>
>> getgrnam_r() uses a preallocated buffer to store a structure
>> containing
>> the broken-out fields of the record in the group database. The
>> size of
>> this buffer is usually sysconf(_SC_GETGR_R_SIZE_MAX) == 1024
>> and it is
>> not enough for groups with a large number of users. In these
>> cases,
>> getgrnam_r() returns -1 and sets errno to ERANGE and the caller
>> can
>> retry with a larger buffer.
>>
>> Fixes:
>> $ semanage login -a -s user_u -r s0-s0:c1.c2 '%largegroup'
>> libsemanage.semanage_direct_commit: semanage_genhomedircon
>> returned error code -1. (Numerical result out of range).
>> OSError: Numerical result out of range
>>
>> Signed-off-by: Petr Lautrbach <plautrba@redhat.com>
>> ---
>> libsemanage/src/genhomedircon.c | 16 +++++++++++++---
>> 1 file changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/libsemanage/src/genhomedircon.c
>> b/libsemanage/src/genhomedircon.c
>> index 591941fb..ac376671 100644
>> --- a/libsemanage/src/genhomedircon.c
>> +++ b/libsemanage/src/genhomedircon.c
>> @@ -1077,10 +1077,20 @@ static int
>> get_group_users(genhomedircon_settings_t * s,
>>
>> const char *grname = selogin + 1;
>>
>> - if (getgrnam_r(grname, &grstorage, grbuf,
>> - (size_t) grbuflen, &group) != 0) {
>> - goto cleanup;
>> + errno = 0;
>> + while (
>> + (retval = getgrnam_r(grname, &grstorage, grbuf,
>> (size_t) grbuflen, &group)) != 0 &&
>> + errno == ERANGE
>> + ) {
>> + char *new_grbuf;
>> + grbuflen *= 2;
>> + new_grbuf = realloc(grbuf, grbuflen);
>> + if (new_grbuf == NULL)
>> + goto cleanup;
>> + grbuf = new_grbuf;
>> }
>
> Hello,
> When reading this for loop, I am concerned about the case where
> the
> member list exceeds 2Go on a system with a 32-bit CPU (where
> sizeof(long) = 4). Even if it seems very unlikely, if this ever
> happens, the loop will become infinite. Would you agree with
> adding
> "&& grbuflen > 0" to the condition of the while statement?
Makes sense, I'll add it. Thanks.
> Anyway, if you do not agree, this patch looks good to me.
> Acked-by: Nicolas Iooss <nicolas.iooss@m4x.org>
>
> Thanks,
> Nicolas
>
>> + if (retval == -1)
>> + goto cleanup;
According to the man page this check is not correct. - "In case of
error, an error number is returned, and NULL is stored in
*result."
I'll fix it as well.
>> if (group == NULL) {
>> ERR(s->h_semanage, "Can't find group named
>> %s\n", grname);
>> --
>> 2.20.1
>>
next prev parent reply other threads:[~2019-02-08 16:46 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-06 19:45 [PATCH] libsemanage: genhomedircon - improve handling large groups Petr Lautrbach
2019-02-07 21:19 ` Nicolas Iooss
2019-02-08 16:46 ` Petr Lautrbach [this message]
2019-02-12 15:20 ` [PATCH v2] " Petr Lautrbach
2019-02-12 21:02 ` Nicolas Iooss
2019-02-15 13:56 ` Petr Lautrbach
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