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Date: Tue, 8 Mar 2022 17:09:58 +0100
From: Christian Göttsche <cgzones@...glemail.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: SElinux list <selinux@...r.kernel.org>,
Paul Moore <paul@...l-moore.com>,
Stephen Smalley <stephen.smalley.work@...il.com>,
Eric Paris <eparis@...isplace.org>,
Nathan Chancellor <nathan@...nel.org>,
Ondrej Mosnacek <omosnace@...hat.com>,
Serge Hallyn <serge@...lyn.com>,
Austin Kim <austin.kim@....com>,
Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>,
Casey Schaufler <casey@...aufler-ca.com>,
Yang Li <yang.lee@...ux.alibaba.com>,
Linux kernel mailing list <linux-kernel@...r.kernel.org>,
llvm@...ts.linux.dev
Subject: Re: [PATCH 5/5] selinux: drop unnecessary NULL check
On Fri, 18 Feb 2022 at 18:31, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> On Thu, Feb 17, 2022 at 6:22 AM Christian Göttsche
> <cgzones@...glemail.com> wrote:
> >
> > Commit e3489f8974e1 ("selinux: kill selinux_sb_get_mnt_opts()")
> > introduced a NULL check on the context after a successful call to
> > security_sid_to_context(). This is on the one hand redundant after
> > checking for success and on the other hand insufficient on an actual
> > NULL pointer, since the context is passed to seq_escape() leading to a
> > call of strlen() on it.
> >
> > Reported by Clang analyzer:
> >
> > In file included from security/selinux/hooks.c:28:
> > In file included from ./include/linux/tracehook.h:50:
> > In file included from ./include/linux/memcontrol.h:13:
> > In file included from ./include/linux/cgroup.h:18:
> > ./include/linux/seq_file.h:136:25: warning: Null pointer passed as 1st argument to string length function [unix.cstring.NullArg]
> > seq_escape_mem(m, src, strlen(src), flags, esc);
> > ^~~~~~~~~~~
>
> I'm guessing there was more to this trace for this instance of this warning?
Yes, complete output appended at the end.
>
> >
> > Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> > ---
> > security/selinux/hooks.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 1e69f88eb326..ac802b99d36c 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -1020,7 +1020,7 @@ static int show_sid(struct seq_file *m, u32 sid)
> > rc = security_sid_to_context(&selinux_state, sid,
> > &context, &len);
> > if (!rc) {
>
> ^ perhaps changing this condition to:
>
> if (!rc && context) {
>
> It might be nice to retain the null ptr check should the semantics of
> security_sid_to_context ever change.
If I read the implementation of security_sid_to_context() and its callees
correctly it should never return 0 (success) and not have populated its 3
argument, unless the passed pointer was zero, which by passing the address
of a stack variable - &context - is not the case).
>
> > - bool has_comma = context && strchr(context, ',');
> > + bool has_comma = strchr(context, ',');
> >
> > seq_putc(m, '=');
> > if (has_comma)
> > --
> > 2.35.1
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers
clang-tidy report:
./include/linux/seq_file.h:136:25: warning: Null pointer passed as 1st
argument to string length function
[clang-analyzer-unix.cstring.NullArg]
seq_escape_mem(m, src, strlen(src), flags, esc);
^
./security/selinux/hooks.c:1041:6: note: Assuming the condition is false
if (!(sbsec->flags & SE_SBINITIALIZED))
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./security/selinux/hooks.c:1041:2: note: Taking false branch
if (!(sbsec->flags & SE_SBINITIALIZED))
^
./security/selinux/hooks.c:1044:6: note: Assuming the condition is false
if (!selinux_initialized(&selinux_state))
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./security/selinux/hooks.c:1044:2: note: Taking false branch
if (!selinux_initialized(&selinux_state))
^
./security/selinux/hooks.c:1047:6: note: Assuming the condition is true
if (sbsec->flags & FSCONTEXT_MNT) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./security/selinux/hooks.c:1047:2: note: Taking true branch
if (sbsec->flags & FSCONTEXT_MNT) {
^
./security/selinux/hooks.c:1050:8: note: Calling 'show_sid'
rc = show_sid(m, sbsec->sid);
^~~~~~~~~~~~~~~~~~~~~~~
./security/selinux/hooks.c:1020:7: note: Value assigned to 'context'
rc = security_sid_to_context(&selinux_state, sid,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./security/selinux/hooks.c:1022:6: note: Assuming 'rc' is 0
if (!rc) {
^~~
./security/selinux/hooks.c:1022:2: note: Taking true branch
if (!rc) {
^
./security/selinux/hooks.c:1023:20: note: Assuming 'context' is null
bool has_comma = context && strchr(context, ',');
^~~~~~~
./security/selinux/hooks.c:1023:28: note: Left side of '&&' is false
bool has_comma = context && strchr(context, ',');
^
./security/selinux/hooks.c:1026:7: note: 'has_comma' is false
if (has_comma)
^~~~~~~~~
./security/selinux/hooks.c:1026:3: note: Taking false branch
if (has_comma)
^
./security/selinux/hooks.c:1028:17: note: Passing null pointer value
via 2nd parameter 's'
seq_escape(m, context, "\"\n\\");
^~~~~~~
./security/selinux/hooks.c:1028:3: note: Calling 'seq_escape'
seq_escape(m, context, "\"\n\\");
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
././include/linux/seq_file.h:152:20: note: Passing null pointer value
via 2nd parameter 'src'
seq_escape_str(m, s, ESCAPE_OCTAL, esc);
^
././include/linux/seq_file.h:152:2: note: Calling 'seq_escape_str'
seq_escape_str(m, s, ESCAPE_OCTAL, esc);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
././include/linux/seq_file.h:136:25: note: Null pointer passed as 1st
argument to string length function
seq_escape_mem(m, src, strlen(src), flags, esc);
^ ~~~
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