The ses->auth_key.len field should be zeroed out during error paths,
along with the 'response' field.
Rationale:
It is possible with a specially crafted SMB2 server to cause the setup
to free the key but keep the session. When the session is recovered
(after a connection drop, for example), the following condition turn
out to be true:
ses->auth_key.len != 0 && ses->auth_key.response == NULL
This will cause the following memcpy() in setup_ntlmv2_rsp() to GPF,
because tiblob == NULL and tilen != 0 (these are the old auth_key values):
memcpy(ses->auth_key.response + baselen, tiblob, tilen);
As seen here (Fedora 20 kernel build 3.16.3-200.fc20.x86_64):
[985673.540019] BUG: unable to handle kernel NULL pointer dereference at (null)
[985673.540049] IP: [<ffffffff8136b7a6>] memcpy+0x6/0x110
[...]
[985673.540957] [<ffffffffa09d28e5>] ? setup_ntlmv2_rsp+0x235/0x9d0 [cifs]
[985673.540980] [<ffffffffa09ccc8a>] ? cifs_small_buf_get+0x1a/0x30 [cifs]
[985673.541003] [<ffffffffa09dfe05>] ? small_smb2_init+0x285/0x510 [cifs]
[985673.541025] [<ffffffffa09d5331>] build_ntlmssp_auth_blob+0x91/0x290 [cifs]
[985673.541047] [<ffffffffa09e06a0>] SMB2_sess_setup+0x1f0/0x590 [cifs]
[...]
Commit applies to 3.18-rc1 and various preceding stable versions.
Signed-off-by: Dan Aloni <dan@xxxxxxxxxxxx>
CC: Steve French <smfrench@xxxxxxxxx>
CC: linux-cifs@xxxxxxxxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
---
fs/cifs/smb2pdu.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 8f1672bb82d5..e0304f258533 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -551,6 +551,7 @@ SMB2_sess_setup(const unsigned int xid, struct cifs_ses *ses,
*/
kfree(ses->auth_key.response);
ses->auth_key.response = NULL;
+ ses->auth_key.len = 0;
/*
* If memory allocation is successful, caller of this function
@@ -713,6 +714,7 @@ ssetup_exit:
rc = server->ops->generate_signingkey(ses);
kfree(ses->auth_key.response);
ses->auth_key.response = NULL;
+ ses->auth_key.len = 0;
if (rc) {
cifs_dbg(FYI,
"SMB3 session key generation failed\n");
@@ -737,6 +739,7 @@ keygen_exit:
if (!server->sign) {
kfree(ses->auth_key.response);
ses->auth_key.response = NULL;
+ ses->auth_key.len = 0;
}
kfree(ses->ntlmssp);
--
1.9.3
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