From 36960e440ccf94349c09fb944930d3bfe4bc473f Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Sat, 3 Nov 2012 09:37:28 -0400 Subject: cifs: fix potential buffer overrun in cifs.idmap handling code The userspace cifs.idmap program generally works with the wbclient libs to generate binary SIDs in userspace. That program defines the struct that holds these values as having a max of 15 subauthorities. The kernel idmapping code however limits that value to 5. When the kernel copies those values around though, it doesn't sanity check the num_subauths value handed back from userspace or from the server. It's possible therefore for userspace to hand us back a bogus num_subauths value (or one that's valid, but greater than 5) that could cause the kernel to walk off the end of the cifs_sid->sub_auths array. Fix this by defining a new routine for copying sids and using that in all of the places that copy it. If we end up with a sid that's longer than expected then this approach will just lop off the "extra" subauths, but that's basically what the code does today already. Better approaches might be to fix this code to reject SIDs with >5 subauths, or fix it to handle the subauths array dynamically. At the same time, change the kernel to check the length of the data returned by userspace. If it's shorter than struct cifs_sid, reject it and return -EIO. If that happens we'll end up with fields that are basically uninitialized. Long term, it might make sense to redefine cifs_sid using a flexarray at the end, to allow for variable-length subauth lists, and teach the code to handle the case where the subauths array being passed in from userspace is shorter than 5 elements. Note too, that I don't consider this a security issue since you'd need a compromised cifs.idmap program. If you have that, you can do all sorts of nefarious stuff. Still, this is probably reasonable for stable. Cc: stable@kernel.org Reviewed-by: Shirish Pargaonkar Signed-off-by: Jeff Layton --- fs/cifs/cifsacl.c | 49 ++++++++++++++++++++----------------------------- 1 file changed, 20 insertions(+), 29 deletions(-) (limited to 'fs') diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c index fc783e264420..0fb15bbbe43c 100644 --- a/fs/cifs/cifsacl.c +++ b/fs/cifs/cifsacl.c @@ -224,6 +224,13 @@ sid_to_str(struct cifs_sid *sidptr, char *sidstr) } } +static void +cifs_copy_sid(struct cifs_sid *dst, const struct cifs_sid *src) +{ + memcpy(dst, src, sizeof(*dst)); + dst->num_subauth = min_t(u8, src->num_subauth, NUM_SUBAUTHS); +} + static void id_rb_insert(struct rb_root *root, struct cifs_sid *sidptr, struct cifs_sid_id **psidid, char *typestr) @@ -248,7 +255,7 @@ id_rb_insert(struct rb_root *root, struct cifs_sid *sidptr, } } - memcpy(&(*psidid)->sid, sidptr, sizeof(struct cifs_sid)); + cifs_copy_sid(&(*psidid)->sid, sidptr); (*psidid)->time = jiffies - (SID_MAP_RETRY + 1); (*psidid)->refcount = 0; @@ -354,7 +361,7 @@ id_to_sid(unsigned long cid, uint sidtype, struct cifs_sid *ssid) * any fields of the node after a reference is put . */ if (test_bit(SID_ID_MAPPED, &psidid->state)) { - memcpy(ssid, &psidid->sid, sizeof(struct cifs_sid)); + cifs_copy_sid(ssid, &psidid->sid); psidid->time = jiffies; /* update ts for accessing */ goto id_sid_out; } @@ -370,14 +377,14 @@ id_to_sid(unsigned long cid, uint sidtype, struct cifs_sid *ssid) if (IS_ERR(sidkey)) { rc = -EINVAL; cFYI(1, "%s: Can't map and id to a SID", __func__); + } else if (sidkey->datalen < sizeof(struct cifs_sid)) { + rc = -EIO; + cFYI(1, "%s: Downcall contained malformed key " + "(datalen=%hu)", __func__, sidkey->datalen); } else { lsid = (struct cifs_sid *)sidkey->payload.data; - memcpy(&psidid->sid, lsid, - sidkey->datalen < sizeof(struct cifs_sid) ? - sidkey->datalen : sizeof(struct cifs_sid)); - memcpy(ssid, &psidid->sid, - sidkey->datalen < sizeof(struct cifs_sid) ? - sidkey->datalen : sizeof(struct cifs_sid)); + cifs_copy_sid(&psidid->sid, lsid); + cifs_copy_sid(ssid, &psidid->sid); set_bit(SID_ID_MAPPED, &psidid->state); key_put(sidkey); kfree(psidid->sidstr); @@ -396,7 +403,7 @@ id_to_sid(unsigned long cid, uint sidtype, struct cifs_sid *ssid) return rc; } if (test_bit(SID_ID_MAPPED, &psidid->state)) - memcpy(ssid, &psidid->sid, sizeof(struct cifs_sid)); + cifs_copy_sid(ssid, &psidid->sid); else rc = -EINVAL; } @@ -675,8 +682,6 @@ int compare_sids(const struct cifs_sid *ctsid, const struct cifs_sid *cwsid) static void copy_sec_desc(const struct cifs_ntsd *pntsd, struct cifs_ntsd *pnntsd, __u32 sidsoffset) { - int i; - struct cifs_sid *owner_sid_ptr, *group_sid_ptr; struct cifs_sid *nowner_sid_ptr, *ngroup_sid_ptr; @@ -692,26 +697,14 @@ static void copy_sec_desc(const struct cifs_ntsd *pntsd, owner_sid_ptr = (struct cifs_sid *)((char *)pntsd + le32_to_cpu(pntsd->osidoffset)); nowner_sid_ptr = (struct cifs_sid *)((char *)pnntsd + sidsoffset); - - nowner_sid_ptr->revision = owner_sid_ptr->revision; - nowner_sid_ptr->num_subauth = owner_sid_ptr->num_subauth; - for (i = 0; i < 6; i++) - nowner_sid_ptr->authority[i] = owner_sid_ptr->authority[i]; - for (i = 0; i < 5; i++) - nowner_sid_ptr->sub_auth[i] = owner_sid_ptr->sub_auth[i]; + cifs_copy_sid(nowner_sid_ptr, owner_sid_ptr); /* copy group sid */ group_sid_ptr = (struct cifs_sid *)((char *)pntsd + le32_to_cpu(pntsd->gsidoffset)); ngroup_sid_ptr = (struct cifs_sid *)((char *)pnntsd + sidsoffset + sizeof(struct cifs_sid)); - - ngroup_sid_ptr->revision = group_sid_ptr->revision; - ngroup_sid_ptr->num_subauth = group_sid_ptr->num_subauth; - for (i = 0; i < 6; i++) - ngroup_sid_ptr->authority[i] = group_sid_ptr->authority[i]; - for (i = 0; i < 5; i++) - ngroup_sid_ptr->sub_auth[i] = group_sid_ptr->sub_auth[i]; + cifs_copy_sid(ngroup_sid_ptr, group_sid_ptr); return; } @@ -1120,8 +1113,7 @@ static int build_sec_desc(struct cifs_ntsd *pntsd, struct cifs_ntsd *pnntsd, kfree(nowner_sid_ptr); return rc; } - memcpy(owner_sid_ptr, nowner_sid_ptr, - sizeof(struct cifs_sid)); + cifs_copy_sid(owner_sid_ptr, nowner_sid_ptr); kfree(nowner_sid_ptr); *aclflag = CIFS_ACL_OWNER; } @@ -1139,8 +1131,7 @@ static int build_sec_desc(struct cifs_ntsd *pntsd, struct cifs_ntsd *pnntsd, kfree(ngroup_sid_ptr); return rc; } - memcpy(group_sid_ptr, ngroup_sid_ptr, - sizeof(struct cifs_sid)); + cifs_copy_sid(group_sid_ptr, ngroup_sid_ptr); kfree(ngroup_sid_ptr); *aclflag = CIFS_ACL_GROUP; } -- cgit v1.2.3-58-ga151 From 3798f47aa276b332c30da499cb4df4577e2f8872 Mon Sep 17 00:00:00 2001 From: Sachin Prabhu Date: Mon, 5 Nov 2012 11:39:32 +0000 Subject: cifs: Do not lookup hashed negative dentry in cifs_atomic_open We do not need to lookup a hashed negative directory since we have already revalidated it before and have found it to be fine. This also prevents a crash in cifs_lookup() when it attempts to rehash the already hashed negative lookup dentry. The patch has been tested using the reproducer at https://bugzilla.redhat.com/show_bug.cgi?id=867344#c28 Cc: # 3.6.x Reported-by: Vit Zahradka Signed-off-by: Sachin Prabhu --- fs/cifs/dir.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c index 7c0a81283645..d3671f2acb29 100644 --- a/fs/cifs/dir.c +++ b/fs/cifs/dir.c @@ -398,7 +398,16 @@ cifs_atomic_open(struct inode *inode, struct dentry *direntry, * in network traffic in the other paths. */ if (!(oflags & O_CREAT)) { - struct dentry *res = cifs_lookup(inode, direntry, 0); + struct dentry *res; + + /* + * Check for hashed negative dentry. We have already revalidated + * the dentry and it is fine. No need to perform another lookup. + */ + if (!d_unhashed(direntry)) + return -ENOENT; + + res = cifs_lookup(inode, direntry, 0); if (IS_ERR(res)) return PTR_ERR(res); -- cgit v1.2.3-58-ga151