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Date: Sat, 11 Jun 2011 07:41:13 -0400
From: Jeff Layton <jlayton@...hat.com>
To: Connor Hansen <cmdkhh@...il.com>
Cc: Suresh Jayaraman <sjayaraman@...e.de>,
Martijn Uffing <mp3project@...ijopen.student.utwente.nl>,
linux-cifs@...r.kernel.org, linux-kernel@...r.kernel.org,
sean finney <seanius@...nius.net>
Subject: Re: [OOPS] 3.0-rc1 cifs
On Fri, 10 Jun 2011 05:49:46 -0700
Connor Hansen <cmdkhh@...il.com> wrote:
> On Fri, Jun 10, 2011 at 5:14 AM, Suresh Jayaraman <sjayaraman@...e.de> wrote:
> > On 06/10/2011 05:33 PM, Connor Hansen wrote:
> >> On Fri, Jun 10, 2011 at 4:37 AM, Jeff Layton <jlayton@...hat.com> wrote:
> >>> On Fri, 10 Jun 2011 02:57:21 +0200 (CEST)
> >>> Uffing <mp3project@...ijopen.student.utwente.nl> 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
> >
> > Yes, I too was hovering around this code path today and it doesn't look
> > correct. Specifically, the call from cifs_dfs_path to CIFSTCon with
> > cifs_tcon as NULL seems wrong. I tried to do dig history a bit with `git
> > blame`, but couldn't figure out the commit that introduced this.
> >
> >
> > --
> > Suresh Jayaraman
> >
>
> git annotate fs/cifs/connect.c
> 1da177e4 (Linus Torvalds 2005-04-16 15:20:36 -0700 2268)
> rc = CIFSTCon(xid, pSesInfo, temp_unc, NULL, nls_codepage);
>
> this was valid at the time to simply get the rc, and the code was checked
> if ((rc == 0) && (tcon != NULL)) { // first use of tcon in
> CIFSTCon back then.....
>
>
> after a loooooong look, i found the patch which changed it
>
> 00e485b0
> commit 00e485b0198ea4f509341373f1d9adb0a5977a2f
> Author: Jeff Layton <jlayton@...hat.com>
> Date: Fri Dec 5 20:41:21 2008 -0500
>
> cifs: store password in tcon
>
> cifs: store password in tcon
>
> Each tcon has its own password for share-level security. Store it in
> the tcon and wipe it clean and free it when freeing the tcon. When
> doing the tree connect with share-level security, use the tcon password
> instead of the session password.
>
> Signed-off-by: Jeff Layton <jlayton@...hat.com>
> Signed-off-by: Steve French <sfrench@...ibm.com>
>
Yep, mea culpa. This patch should fix it. Martin, can you test it?
Anyone else have comments?
Thanks...
-----------------------[snip]--------------------
[PATCH] cifs: correctly handle NULL tcon pointer in CIFSTCon
Long ago (in commit 00e485b0), I added some code to handle share-level
passwords in CIFSTCon. That code ignored the fact that it's legit to
pass in a NULL tcon pointer when connecting to the IPC$ share on the
server.
This wasn't really a problem until recently as we only called CIFSTCon
this way when the server returned -EREMOTE. With the introduction of
commit c1508ca2 however, it gets called this way on every mount, causing
an oops when share-level security is in effect.
Fix this by simply treating a NULL tcon pointer as if user-level
security were in effect. I'm not aware of any servers that protect the
IPC$ share with a specific password anyway. Also, add a comment to the
top of CIFSTCon to ensure that we don't make the same mistake again.
Reported-by: Martijn Uffing <mp3project@...ijopen.student.utwente.nl>
Signed-off-by: Jeff Layton <jlayton@...hat.com>
---
fs/cifs/connect.c | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 7b6cad2..fa5a5d7 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3174,6 +3174,10 @@ out:
return rc;
}
+/*
+ * Issue a TREE_CONNECT request. Note that for IPC$ shares, that the tcon
+ * pointer may be NULL.
+ */
int
CIFSTCon(unsigned int xid, struct cifs_ses *ses,
const char *tree, struct cifs_tcon *tcon,
@@ -3208,7 +3212,7 @@ CIFSTCon(unsigned int xid, struct cifs_ses *ses,
pSMB->AndXCommand = 0xFF;
pSMB->Flags = cpu_to_le16(TCON_EXTENDED_SECINFO);
bcc_ptr = &pSMB->Password[0];
- if ((ses->server->sec_mode) & SECMODE_USER) {
+ if (!tcon || (ses->server->sec_mode & SECMODE_USER)) {
pSMB->PasswordLength = cpu_to_le16(1); /* minimum */
*bcc_ptr = 0; /* password is null byte */
bcc_ptr++; /* skip password */
--
1.7.5.2
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