Hi Colin,
Thanks for reporting this. I'll submit a fix.
Regards,
Shyam
-----Original Message-----
From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Sent: Wednesday, February 24, 2021 6:14 PM
To: Shyam Prasad <Shyam.Prasad@xxxxxxxxxxxxx>
Cc: Steve French <sfrench@xxxxxxxxx>; linux-cifs@xxxxxxxxxxxxxxx; samba-technical@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
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@xxxxxxxxxxxxx>
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.
