On Wed, 24 Jan 2024 at 00:47, Kees Cook <[email protected]> wrote: > > 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 <[email protected]> > Closes: https://github.com/ClangBuiltLinux/linux/issues/1966 [1] > Link: https://github.com/llvm/llvm-project/issues/77813 [2] > Cc: Steve French <[email protected]> > Cc: Paulo Alcantara <[email protected]> > Cc: Ronnie Sahlberg <[email protected]> > Cc: Shyam Prasad N <[email protected]> > Cc: Tom Talpey <[email protected]> > Cc: [email protected] > Cc: [email protected] > Signed-off-by: Kees Cook <[email protected]> > --- > 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 ef4c2e3c9fa6..6322f0f68a17 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;
Is 'user' guaranteed to be 16-bit aligned? > } > > rc = crypto_shash_update(ses->server->secmech.hmacmd5, > -- > 2.34.1 > >
