[PATCH 6.6 022/299] smb: Work around Clang __bdos() type confusion

Greg Kroah-Hartman
2024-02-27T13:47:29Z

From: Kees Cook <keescook@chromium.org>

[ Upstream commit 8deb05c84b63b4fdb8549e08942867a68924a5b8 ]

Recent versions of Clang gets confused about the possible size of the
"user" allocation, and CONFIG_FORTIFY_SOURCE ends up emitting a
warning[1]:

repro.c:126:4: warning: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
126 | __write_overflow_field(p_size_field, size);
| ^

for this memset():

int len;
__le16 *user;
...
len = ses->user_name ? strlen(ses->user_name) : 0;
user = kmalloc(2 + (len * 2), GFP_KERNEL);
...
if (len) {
...
} else {
memset(user, '\0', 2);
}

While Clang works on this bug[2], switch to using a direct assignment,
which avoids memset() entirely which both simplifies the code and silences
the false positive warning. (Making "len" size_t also silences the
warning, but the direct assignment seems better.)

Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://github.com/ClangBuiltLinux/linux/issues/1966 [1]
Link: https://github.com/llvm/llvm-project/issues/77813 [2]
Cc: Steve French <sfrench@samba.org>
Cc: Paulo Alcantara <pc@manguebit.com>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: linux-cifs@vger.kernel.org
Cc: llvm@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/smb/client/cifsencrypt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/smb/client/cifsencrypt.c b/fs/smb/client/cifsencrypt.c
index ef4c2e3c9fa61..6322f0f68a176 100644
--- a/fs/smb/client/cifsencrypt.c
+++ b/fs/smb/client/cifsencrypt.c
@@ -572,7 +572,7 @@ static int calc_ntlmv2_hash(struct cifs_ses *ses, char *ntlmv2_hash,
len = cifs_strtoUTF16(user, ses->user_name, len, nls_cp);
UniStrupr(user);
} else {
- memset(user, '\0', 2);
+ *(u16 *)user = 0;
}

rc = crypto_shash_update(ses->server->secmech.hmacmd5,
--
2.43.0