[EXTERNAL] re: cifs: Retain old ACEs when converting between mode bits and ACL.

[Steve French]

Add the RB from Rohith and merged into cifs-2.6.git for-next

On Wed, Feb 24, 2021 at 10:58 AM Shyam Prasad N via samba-technical
<samba-technical at lists.samba.org> wrote:
>
> Hi Steve,
>
> Please accept this fix for the bug that Colin pointed out.
> This can be hit if the server has a corrupted SD, or it got corrupted
> over the network.
> We used to ignore the ACL in such a case (which in combination with my
> patches caused the issue). But I think we should be returning an error
> immediately.
>
> Regards,
> Shyam
>
> On Wed, Feb 24, 2021 at 7:16 AM Shyam Prasad <Shyam.Prasad at microsoft.com> wrote:
> >
> > Hi Colin,
> >
> > Thanks for reporting this. I'll submit a fix.
> >
> > Regards,
> > Shyam
> >
> > -----Original Message-----
> > From: Colin Ian King <colin.king at canonical.com>
> > Sent: Wednesday, February 24, 2021 6:14 PM
> > To: Shyam Prasad <Shyam.Prasad at microsoft.com>
> > Cc: Steve French <sfrench at samba.org>; linux-cifs at vger.kernel.org; samba-technical at lists.samba.org; linux-kernel at vger.kernel.org
> > Subject: [EXTERNAL] re: cifs: Retain old ACEs when converting between mode bits and ACL.
> >
> > Hi,
> >
> > Static analysis on linux-next with Coverity had detected a potential null pointer dereference with the following commit:
> >
> > commit f5065508897a922327f32223082325d10b069ebc
> > Author: Shyam Prasad N <sprasad at microsoft.com>
> > Date:   Fri Feb 12 04:38:43 2021 -0800
> >
> >     cifs: Retain old ACEs when converting between mode bits and ACL.
> >
> > The analysis is as follows:
> >
> > 1258 /* Convert permission bits from mode to equivalent CIFS ACL */
> > 1259 static int build_sec_desc(struct cifs_ntsd *pntsd, struct cifs_ntsd *pnntsd,
> > 1260        __u32 secdesclen, __u32 *pnsecdesclen, __u64 *pnmode, kuid_t
> > uid, kgid_t gid,
> > 1261        bool mode_from_sid, bool id_from_sid, int *aclflag)
> > 1262 {
> > 1263        int rc = 0;
> > 1264        __u32 dacloffset;
> > 1265        __u32 ndacloffset;
> > 1266        __u32 sidsoffset;
> > 1267        struct cifs_sid *owner_sid_ptr, *group_sid_ptr;
> > 1268        struct cifs_sid *nowner_sid_ptr = NULL, *ngroup_sid_ptr = NULL;
> >
> >     1. assign_zero: Assigning: dacl_ptr = NULL.
> >
> > 1269        struct cifs_acl *dacl_ptr = NULL;  /* no need for SACL ptr */
> > 1270        struct cifs_acl *ndacl_ptr = NULL; /* no need for SACL ptr */
> > 1271        char *end_of_acl = ((char *)pntsd) + secdesclen;
> > 1272        u16 size = 0;
> > 1273
> > 1274        dacloffset = le32_to_cpu(pntsd->dacloffset);
> >
> >     2. Condition dacloffset, taking false branch.
> >
> > 1275        if (dacloffset) {
> > 1276                dacl_ptr = (struct cifs_acl *)((char *)pntsd +
> > dacloffset);
> > 1277                if (end_of_acl < (char *)dacl_ptr +
> > le16_to_cpu(dacl_ptr->size)) {
> > 1278                        cifs_dbg(VFS, "Existing ACL size is wrong.
> > Discarding old ACL\n");
> > 1279                        dacl_ptr = NULL;
> >
> > NOTE: dacl_ptr is set to NULL and dacloffset is true
> >
> > 1280                }
> > 1281        }
> > 1282
> > 1283        owner_sid_ptr = (struct cifs_sid *)((char *)pntsd +
> > 1284                        le32_to_cpu(pntsd->osidoffset));
> > 1285        group_sid_ptr = (struct cifs_sid *)((char *)pntsd +
> > 1286                        le32_to_cpu(pntsd->gsidoffset));
> > 1287
> >
> >     3. Condition pnmode, taking true branch.
> >     4. Condition *pnmode != 18446744073709551615ULL, taking false branch.
> >
> > 1288        if (pnmode && *pnmode != NO_CHANGE_64) { /* chmod */
> > 1289                ndacloffset = sizeof(struct cifs_ntsd);
> > 1290                ndacl_ptr = (struct cifs_acl *)((char *)pnntsd +
> > ndacloffset);
> > 1291                ndacl_ptr->revision =
> > 1292                        dacloffset ? dacl_ptr->revision :
> > cpu_to_le16(ACL_REVISION);
> > 1293
> > 1294                ndacl_ptr->size = cpu_to_le16(0);
> > 1295                ndacl_ptr->num_aces = cpu_to_le32(0);
> > 1296
> > 1297                rc = set_chmod_dacl(dacl_ptr, ndacl_ptr,
> > owner_sid_ptr, group_sid_ptr,
> > 1298                                    pnmode, mode_from_sid);
> > 1299
> > 1300                sidsoffset = ndacloffset + le16_to_cpu(ndacl_ptr->size);
> > 1301                /* copy the non-dacl portion of secdesc */
> > 1302                *pnsecdesclen = copy_sec_desc(pntsd, pnntsd, sidsoffset,
> > 1303                                NULL, NULL);
> > 1304
> > 1305                *aclflag |= CIFS_ACL_DACL;
> > 1306        } else {
> > 1307                ndacloffset = sizeof(struct cifs_ntsd);
> > 1308                ndacl_ptr = (struct cifs_acl *)((char *)pnntsd +
> > ndacloffset);
> >
> >     5. Condition dacloffset, taking false branch.
> >
> > 1309                ndacl_ptr->revision =
> > 1310                        dacloffset ? dacl_ptr->revision :
> > cpu_to_le16(ACL_REVISION);
> >
> >     Explicit null dereferenced (FORWARD_NULL)
> >
> >     6. var_deref_op: Dereferencing null pointer dacl_ptr.
> >
> > 1311                ndacl_ptr->num_aces = dacl_ptr->num_aces;
> >
> >
> > Line 1309..1311, when dacloffset and dacl_ptr is null we hit a null ptr dereference on dacl_ptr.
> >
>
>
> --
> Regards,
> Shyam



-- 
Thanks,

Steve