Re: [OOPS] 3.0-rc1 cifs

[Connor Hansen]

On Fri, Jun 10, 2011 at 4:37 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> On Fri, 10 Jun 2011 02:57:21 +0200 (CEST)
>  Uffing <mp3project@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>
>> <snip>
>> > call in get_dfs_path()
>> > rc = CIFSTCon(xid, pSesInfo, temp_unc, NULL, nls_codepage);
>> >
>> > function header for CIFSTCon
>> > int  CIFSTCon(unsigned int xid, struct cifs_ses *ses,
>> >          const char *tree, struct cifs_tcon *tcon,
>> >          const struct nls_table *nls_codepage)
>> >
>> > get_dfs_path() is passing struct cifs_tcon *tcon as NULL
>> >
>> > from config:  CONFIG_CIFS_WEAK_PW_HASH=y
>> >
>> > in CIFSTCon
>> >
>> > #ifdef CONFIG_CIFS_WEAK_PW_HASH
>> > 3222                 if ((global_secflags & CIFSSEC_MAY_LANMAN) &&
>> > 3223                     (ses->server->secType == LANMAN))
>> > 3224                         calc_lanman_hash(tcon->password,
>> > ses->server->cryptkey,
>> >
>> > in calc_lanman_hash tcon is dereferenced(tcon->password) without being
>> > checked if null
>> >
>> > 3225                                          ses->server->sec_mode &
>> > 3226                                             SECMODE_PW_ENCRYPT ?
>> > true : false,
>> > 3227                                          bcc_ptr);
>> > 3228                 else
>> > 3229 #endif /* CIFS_WEAK_PW_HASH */
>> >
>> > Connor
>>
>>
>> Ave all
>>
>> I recompiled  kernel 3.0-rc1 (hadn't enabled CONFIG_DEBUG_INFO=y) and put
>> the oops (with the new adresses) through gdb per instruction of Jeff. And
>> Connor was spot on!
>>
>> <qoute oops>
>> BUG: unable to handle kernel NULL pointer dereference at 00000000000000a0
>> IP: [<ffffffffa041e286>] CIFSTCon+0xf6/0x4d0 [cifs]
>> </qoute oops>
>>
>> <qoute gdb>
>> This GDB was configured as "x86_64-linux-gnu".
>> For bug reporting instructions, please see:
>> <http://www.gnu.org/software/gdb/bugs/>...
>> Reading symbols from
>> /lib/modules/3.0.0-rc1-debug/kernel/fs/cifs/cifs.ko...done.
>> (gdb) list *(CIFSTCon+0xf6)
>> 0xc2b6 is in CIFSTCon (fs/cifs/connect.c:3230).
>> 3225                                             ses->server->sec_mode &
>> 3226                                                SECMODE_PW_ENCRYPT ?
>> true : false,
>> 3227                                             bcc_ptr);
>> 3228                    else
>> 3229    #endif /* CIFS_WEAK_PW_HASH */
>> 3230                    rc = SMBNTencrypt(tcon->password,
>> ses->server->cryptkey,
>> 3231                                            bcc_ptr);
>> 3232
>> 3233                    bcc_ptr += CIFS_AUTH_RESP_SIZE;
>> 3234                    if (ses->capabilities & CAP_UNICODE) {
>> (gdb)
>> </qoute gdb>
>>
>
> (cc'ing Sean F. since I suspect this regression is due to his changes)
>
> Thanks for the analysis, Martijn and Connor...
>
> What sort of server are you mounting here? It looks like it's using
> share-level security, so it's either very old or is a samba server
> configured that way.
>
> I suspect that commit c1508ca236 is the culprit. With that, we call
> into expand_dfs_referral on every mount attempt. Previously we only
> called into there when we got back  an EREMOTE error and that would
> have been unlikely on a share-level security connection.
>
> I think there are several possible solutions, but since Sean was in
> here most recently I'd like to have his opinion.

I don't know enough about cifs but this call in fs/cifs/connect.c

2268: rc = CIFSTCon(xid, pSesInfo, temp_unc, NULL, nls_codepage);

will always result in a null pointer derefence as CIFSTCon uses the
cifs_tcon struct for passwords without verification

either we need to check for tcon for null in CIFSTCon before use, or
change get_dfs_path to get the cifs_tcon info and pass it to the
CIFSTCon function. But again I don't know enough about cifs to know
the best approach

Connor
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
>
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