[PATCH] cifs: check kmalloc before use

[Nicholas Mc Guire]

The kmalloc was not being checked - if it fails issue a warning
and return -ENOMEM to the caller.

Signed-off-by: Nicholas Mc Guire <hofrat@xxxxxxxxx>
Fixes: b8da344b74c8 ("cifs: dynamic allocation of ntlmssp blob")
---

Problem was located with an experimental coccinelle script

Both call-sites will expect non-0 to indicate error so -ENOMEM
should be OK here. Setting buflen to 0 seems to be the expected
behavior on failure although it will not be checked/used at
the call-sites - probably this could be removed here as well as
in the handling of authentication error (preceding this change)
it was just retained for consistency.

Patch was compile tested with: x86_64_defconfig + CONFIG_CIFS=y
(with sparse and smatch warning unrelated to proposed change)

Patch is against 4.18 (localversion-next is next-20180823)

 fs/cifs/sess.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index 8b0502c..aa23c00 100644
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -398,6 +398,12 @@ int build_ntlmssp_auth_blob(unsigned char **pbuffer,
 		goto setup_ntlmv2_ret;
 	}
 	*pbuffer = kmalloc(size_of_ntlmssp_blob(ses), GFP_KERNEL);
+	if (!*pbuffer) {
+		rc = -ENOMEM;
+		cifs_dbg(VFS, "Error %d during NTLMSSP allocation\n", rc);
+		*buflen = 0;
+		goto setup_ntlmv2_ret;
+	}
 	sec_blob = (AUTHENTICATE_MESSAGE *)*pbuffer;
 
 	memcpy(sec_blob->Signature, NTLMSSP_SIGNATURE, 8);
-- 
2.1.4