From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mimi Zohar Date: Thu, 31 May 2018 15:00:39 +0000 Subject: Re: [PATCH] EVM: prevent array underflow in evm_write_xattrs() Message-Id: <1527778839.3427.14.camel@linux.vnet.ibm.com> List-Id: References: <20180529131128.3rkzzv66uy6h5ts7@kili.mountain> In-Reply-To: <20180529131128.3rkzzv66uy6h5ts7@kili.mountain> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Dan Carpenter , Matthew Garrett Cc: James Morris , "Serge E. Hallyn" , linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, kernel-janitors@vger.kernel.org On Tue, 2018-05-29 at 16:11 +0300, Dan Carpenter wrote: > If the user sets xattr->name[0] to NUL then we would read one character > before the start of the array. This bug seems harmless as far as I can > see but perhaps it would trigger a warning in KASAN. > > Fixes: fa516b66a1bf ("EVM: Allow runtime modification of the set of verified xattrs") > Signed-off-by: Dan Carpenter Thanks, this patch is now queued in the next-integrity branch. Mimi > --- > The user can pass a zeroed buffer to memdup_user_nul() so we can't rely > on "count" to test this. > > diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c > index a7a0a1acae99..94c739180a0b 100644 > --- a/security/integrity/evm/evm_secfs.c > +++ b/security/integrity/evm/evm_secfs.c > @@ -207,7 +207,7 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf, > > /* Remove any trailing newline */ > len = strlen(xattr->name); > - if (xattr->name[len-1] = '\n') > + if (len && xattr->name[len-1] = '\n') > xattr->name[len-1] = '\0'; > > if (strcmp(xattr->name, ".") = 0) { >