Re: [EXTERNAL] re: cifs: Retain old ACEs when converting between mode bits and ACL.
From: Steve French
Date: Wed Feb 24 2021 - 13:22:56 EST
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@xxxxxxxxxxxxxxx> wrote:
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Hi Steve,
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Please accept this fix for the bug that Colin pointed out.
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This can be hit if the server has a corrupted SD, or it got corrupted
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over the network.
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We used to ignore the ACL in such a case (which in combination with my
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patches caused the issue). But I think we should be returning an error
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immediately.
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Regards,
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Shyam
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On Wed, Feb 24, 2021 at 7:16 AM Shyam Prasad <Shyam.Prasad@xxxxxxxxxxxxx> wrote:
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> Hi Colin,
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> Thanks for reporting this. I'll submit a fix.
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> Regards,
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> Shyam
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> -----Original Message-----
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> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
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> Sent: Wednesday, February 24, 2021 6:14 PM
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> To: Shyam Prasad <Shyam.Prasad@xxxxxxxxxxxxx>
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> Cc: Steve French <sfrench@xxxxxxxxx>; linux-cifs@xxxxxxxxxxxxxxx; samba-technical@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
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> Subject: [EXTERNAL] re: cifs: Retain old ACEs when converting between mode bits and ACL.
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> Hi,
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> Static analysis on linux-next with Coverity had detected a potential null pointer dereference with the following commit:
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> commit f5065508897a922327f32223082325d10b069ebc
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> Author: Shyam Prasad N <sprasad@xxxxxxxxxxxxx>
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> Date: Fri Feb 12 04:38:43 2021 -0800
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> cifs: Retain old ACEs when converting between mode bits and ACL.
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> The analysis is as follows:
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> 1258 /* Convert permission bits from mode to equivalent CIFS ACL */
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> 1259 static int build_sec_desc(struct cifs_ntsd *pntsd, struct cifs_ntsd *pnntsd,
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> 1260 __u32 secdesclen, __u32 *pnsecdesclen, __u64 *pnmode, kuid_t
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> uid, kgid_t gid,
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> 1261 bool mode_from_sid, bool id_from_sid, int *aclflag)
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> 1262 {
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> 1263 int rc = 0;
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> 1264 __u32 dacloffset;
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> 1265 __u32 ndacloffset;
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> 1266 __u32 sidsoffset;
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> 1267 struct cifs_sid *owner_sid_ptr, *group_sid_ptr;
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> 1268 struct cifs_sid *nowner_sid_ptr = NULL, *ngroup_sid_ptr = NULL;
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> 1. assign_zero: Assigning: dacl_ptr = NULL.
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> 1269 struct cifs_acl *dacl_ptr = NULL; /* no need for SACL ptr */
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> 1270 struct cifs_acl *ndacl_ptr = NULL; /* no need for SACL ptr */
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> 1271 char *end_of_acl = ((char *)pntsd) + secdesclen;
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> 1272 u16 size = 0;
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> 1273
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> 1274 dacloffset = le32_to_cpu(pntsd->dacloffset);
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> 2. Condition dacloffset, taking false branch.
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> 1275 if (dacloffset) {
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> 1276 dacl_ptr = (struct cifs_acl *)((char *)pntsd +
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> dacloffset);
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> 1277 if (end_of_acl < (char *)dacl_ptr +
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> le16_to_cpu(dacl_ptr->size)) {
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> 1278 cifs_dbg(VFS, "Existing ACL size is wrong.
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> Discarding old ACL\n");
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> 1279 dacl_ptr = NULL;
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> NOTE: dacl_ptr is set to NULL and dacloffset is true
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> 1280 }
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> 1281 }
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> 1282
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> 1283 owner_sid_ptr = (struct cifs_sid *)((char *)pntsd +
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> 1284 le32_to_cpu(pntsd->osidoffset));
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> 1285 group_sid_ptr = (struct cifs_sid *)((char *)pntsd +
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> 1286 le32_to_cpu(pntsd->gsidoffset));
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> 1287
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> 3. Condition pnmode, taking true branch.
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> 4. Condition *pnmode != 18446744073709551615ULL, taking false branch.
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> 1288 if (pnmode && *pnmode != NO_CHANGE_64) { /* chmod */
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> 1289 ndacloffset = sizeof(struct cifs_ntsd);
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> 1290 ndacl_ptr = (struct cifs_acl *)((char *)pnntsd +
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> ndacloffset);
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> 1291 ndacl_ptr->revision =
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> 1292 dacloffset ? dacl_ptr->revision :
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> cpu_to_le16(ACL_REVISION);
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> 1293
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> 1294 ndacl_ptr->size = cpu_to_le16(0);
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> 1295 ndacl_ptr->num_aces = cpu_to_le32(0);
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> 1296
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> 1297 rc = set_chmod_dacl(dacl_ptr, ndacl_ptr,
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> owner_sid_ptr, group_sid_ptr,
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> 1298 pnmode, mode_from_sid);
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> 1299
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> 1300 sidsoffset = ndacloffset + le16_to_cpu(ndacl_ptr->size);
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> 1301 /* copy the non-dacl portion of secdesc */
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> 1302 *pnsecdesclen = copy_sec_desc(pntsd, pnntsd, sidsoffset,
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> 1303 NULL, NULL);
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> 1304
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> 1305 *aclflag |= CIFS_ACL_DACL;
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> 1306 } else {
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> 1307 ndacloffset = sizeof(struct cifs_ntsd);
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> 1308 ndacl_ptr = (struct cifs_acl *)((char *)pnntsd +
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> ndacloffset);
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> 5. Condition dacloffset, taking false branch.
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> 1309 ndacl_ptr->revision =
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> 1310 dacloffset ? dacl_ptr->revision :
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> cpu_to_le16(ACL_REVISION);
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> Explicit null dereferenced (FORWARD_NULL)
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> 6. var_deref_op: Dereferencing null pointer dacl_ptr.
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> 1311 ndacl_ptr->num_aces = dacl_ptr->num_aces;
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> Line 1309..1311, when dacloffset and dacl_ptr is null we hit a null ptr dereference on dacl_ptr.
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--
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Regards,
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Shyam
--
Thanks,
Steve