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Message-ID: <CAH2r5mue5TxydZJFiV=z8eDPfYDDtnj-CfT7ac+tHyz+s5XYYQ@mail.gmail.com>
Date: Wed, 24 Feb 2021 12:21:35 -0600
From: Steve French <smfrench@...il.com>
To: Shyam Prasad N <nspmangalore@...il.com>
Cc: Shyam Prasad <Shyam.Prasad@...rosoft.com>,
rohiths msft <rohiths.msft@...il.com>,
Steve French <sfrench@...ba.org>,
Colin Ian King <colin.king@...onical.com>,
"samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>
Subject: Re: [EXTERNAL] re: cifs: Retain old ACEs when converting between mode
bits and ACL.
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@...ts.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@...rosoft.com> wrote:
> >
> > Hi Colin,
> >
> > Thanks for reporting this. I'll submit a fix.
> >
> > Regards,
> > Shyam
> >
> > -----Original Message-----
> > From: Colin Ian King <colin.king@...onical.com>
> > Sent: Wednesday, February 24, 2021 6:14 PM
> > To: Shyam Prasad <Shyam.Prasad@...rosoft.com>
> > Cc: Steve French <sfrench@...ba.org>; linux-cifs@...r.kernel.org; samba-technical@...ts.samba.org; linux-kernel@...r.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@...rosoft.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
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