On Mon, 2013-12-02 at 17:33 +0100, Lukas Slebodnik wrote: > On (02/12/13 09:38), Simo Sorce wrote: > >On Fri, 2013-11-29 at 15:25 +0100, Michal Židek wrote: > >> On 11/28/2013 08:40 PM, Simo Sorce wrote: > >> > On Thu, 2013-11-28 at 11:20 +0100, Jakub Hrozek wrote: > >> >> On Tue, Nov 19, 2013 at 04:08:40PM +0100, Michal Židek wrote: > >> >>> On 11/14/2013 01:14 PM, Lukas Slebodnik wrote:>>From > >> >>> 45336d3596b8d93ebf866c727c566169c404b60c Mon Sep 17 00:00:00 2001 > >> >>>>>> From: Michal Zidek<[email protected]> > >> >>>>>> Date: Tue, 10 Sep 2013 23:09:04 +0200 > >> >>>>>> Subject: [PATCH 6/7] Properly align buffer when storing pointers. > >> >>>>>> > >> >>>>>> Properly align buffer address to sizeof(char *) when storing > >> >>>>>> pointers to string and disable alignment warnings with #pragma. > >> >>>>>> > >> >>>>>> resolves: > >> >>>>>> https://fedorahosted.org/sssd/ticket/1359 > >> >>>>>> --- > >> >>>>>> src/sss_client/nss_group.c | 5 +++-- > >> >>>>>> src/sss_client/nss_mc_group.c | 3 +++ > >> >>>>>> src/sss_client/nss_services.c | 4 ++-- > >> >>>>>> 3 files changed, 8 insertions(+), 4 deletions(-) > >> >>>>>> > >> >>>>>> diff --git a/src/sss_client/nss_group.c b/src/sss_client/nss_group.c > >> >>>>>> index a7fb093..68e14d3 100644 > >> >>>>>> --- a/src/sss_client/nss_group.c > >> >>>>>> +++ b/src/sss_client/nss_group.c > >> >>>>>> @@ -233,14 +233,15 @@ static int sss_nss_getgr_readrep(struct > >> >>> sss_nss_gr_rep *pr, > >> >>>>>> NULL); > >> >>>>>> if (ret != EOK) return ret; > >> >>>>>> > >> >>>>>> - /* Make sure pr->buffer[i+pad] is 32 bit aligned */ > >> >>>>>> + /* Make sure pr->buffer[i+pad] is aligned to sizeof(char *) */ > >> >>>>>> pad = 0; > >> >>>>>> - while((i + pad) % 4) { > >> >>>>>> + while((i + pad) % sizeof(char *)) { > >> >>>> I am not sure about this. There was comment; > >> >>>> "Make sure pr->buffer[i+pad] is 32 bit aligned" > >> >>>> > >> >>>> And you changed alignment to 64-bits on x86_64 and to 32-bits on i386 > >> >>>> platform. > >> >>>> This is a client code, so some more experienced should tell what > >> >>>> is the right solution. > >> >>>> > >> >>> > >> >>> Aligning the address to 4 bytes and then using it as the beginning > >> >>> of array of pointers is simply wrong and should be fixed. So I think > >> >>> it was a mistake in both the code and the comment (maybe one led to > >> >>> the other). But is is possible that I am reading the code wrong. > >> >>> > >> >>> Michal > >> >> > >> >> Simo, can you check this patch, please? According to git history, you > >> >> added code that aligned to 32bits, do you remember what was the purpose? > >> > > >> > If I read this snippet correctly this is wrong. > >> > The pointer size differs between x86_64 and i686, so single handedly you > >> > are breaking backwards compatibility on x86_64 and breaking multilib > >> > compatibility. > >> > > >> > 32bit alignment is a conscious choice, do not change it. > >> > > >> > Michael we are not dealing with real addresses here, and what is the > >> > real arch pointer type is simply irrelevant. > >> > >> We are dealing with real addresses. > > > >Apologies, I did think it was dealing with the packet buffer and not the > >group structure buffer. > >I wonder if we should change some struct names here, after so long I had > >to dig quite a bit in the code to understand it fully again, and 100% of > >the issue was in the variable names used. > > > >> This is were the array of addresses starts (src/sss_client/nss_group.c) > >> 243 pr->result->gr_mem = (char **)&(pr->buffer[i+pad]); > > ^^^^^^^ > > > >Ok I do see the issue now, I forgot that the actual strings buffer had > >been 32bit aligned by a later patch, the original design did not do > >this. > > > >And I really wonder if this is needed. Do strings need to start on an > >aligned boundary in ARM ? > > > >> This is why i+pad needs to be aligned to sizeof(char*) not 4 bytes. > > > >Yes, if ARM requires the first element of a char array to be aligned > >then we need to align based on the arch pointer size I guess. I just > >find this strange. > > > >> Here we store terminating NULL > >> 250 pr->result->gr_mem[mem_num] = NULL; /* terminate array */ > >> > >> Here we copy all the members (look at line 253. we are really storing > >> the address): > >> 252 for (l = 0; l < mem_num; l++) { > >> 253 pr->result->gr_mem[l] = &(pr->buffer[ptmem]); > >> 254 ret = sss_readrep_copy_string(sbuf, &i, > >> 255 &slen, &dlen, > >> 256 &pr->result->gr_mem[l], > >> 257 &glen); > >> 258 if (ret != EOK) return ret; > >> 259 > >> 260 ptmem += glen + 1; > >> 261 } > >> > >> One important thing to note is that we are not changing the > >> client<-->responder protocol here (pr->buffer has nothing to do with > >> it). Maybe it will be more clear if we look at types we are working with: > >> > >> pr is pointer to > >> type = struct sss_nss_gr_rep { > >> struct group *result; > >> char *buffer; > >> size_t buflen; > >> } > > > >I think maybe we should change buffer -> mem_names_buf and buflen -> > >mem_names_size ? > > > >> pr->result is pointer to > >> type = struct group { > >> char *gr_name; > >> char *gr_passwd; > >> __gid_t gr_gid; > >> char **gr_mem; > >> } > >> > >> As you can see, gr_mem is really char **. The strings are stored in the > >> same buffer as the array of pointers that are pointing to them (because > >> where else would we store it, we have just one buffer from glibc, that > >> we can enlarge by returning ERANGE), but the pointers are not relative. > >> The whole is glibc structure, that we are filling in this function. > > > >True, I still am surprised ARM wants strings aligned, but if that is > >really required, then your patch is correct. > > > String needn't be aligned, but "array of char pointers" (char **gr_mem) must > be.
Ah, of course, palm -> head. > I checked source code of nslcd and result->gr_mem is aligned sizeof(char *) > > _nss_ldap_getgrnam_r > :-> read_group > :-> READ_BUF_STRINGLIST > :-> BUF_ALLOC > :-> BUF_ALIGN > > I am attaching two files nslcd_macros.c(some macros from nslcd) and > group_postproc.c (expanded version of function read_group) Please proceed in this direction. Simo. -- Simo Sorce * Red Hat, Inc * New York _______________________________________________ sssd-devel mailing list [email protected] https://lists.fedorahosted.org/mailman/listinfo/sssd-devel
