Re: [PATCH ima-evm-utils] evmctl: fix memory leak in get_password

[Bruno Meneguele <bmeneg@redhat.com>]

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On Wed, Aug 11, 2021 at 10:52:00AM -0400, Mimi Zohar wrote:
> Hi Bruno,
> 
> On Tue, 2021-08-10 at 17:28 -0300, Bruno Meneguele wrote:
> > The variable "password" is not freed nor returned in case get_password()
> > succeeds. Instead of using an intermediary variable ("pwd") for returning
> > the value, use the same "password" var. Issue found by Coverity scan tool.
> > 
> > src/evmctl.c:2565: leaked_storage: Variable "password" going out of scope
> >     leaks the storage it points to.
> > 
> > Signed-off-by: Bruno Meneguele <bmeneg@redhat.com>
> > ---
> >  src/evmctl.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> > 
> > diff --git a/src/evmctl.c b/src/evmctl.c
> > index 7a6f2021aa92..b49c7910a4a7 100644
> > --- a/src/evmctl.c
> > +++ b/src/evmctl.c
> > @@ -2601,8 +2601,9 @@ static struct option opts[] = {
> >  static char *get_password(void)
> >  {
> >  	struct termios flags, tmp_flags;
> > -	char *password, *pwd;
> > +	char *password;
> >  	int passlen = 64;
> > +	bool err = false;
> >  
> >  	password = malloc(passlen);
> >  	if (!password) {
> > @@ -2622,16 +2623,24 @@ static char *get_password(void)
> >  	}
> >  
> >  	printf("PEM password: ");
> > -	pwd = fgets(password, passlen, stdin);
> > +	if (fgets(password, passlen, stdin) == NULL) {
> > +		perror("fgets");
> > +		/* we still need to restore the terminal */
> > +		err = true;
> > +	}
> 
> From the fgets manpage: 
>    fgets() returns s on success, and NULL on error
>    or  when  end  of  file
>    occurs while no characters have been read. 
> 

Yes, I was considering "end of file while no characters have been read"
as an invalid password. The error message is misleading though, which
can be fixed.

> >  	/* restore terminal */
> >  	if (tcsetattr(fileno(stdin), TCSANOW, &flags) != 0) {
> >  		perror("tcsetattr");
> > +		err = true;
> > +	}
> > +
> > +	if (err) {
> >  		free(password);
> >  		return NULL;
> >  	}
> > 
> > -	return pwd;
> > +	return password;
> 
> Wouldn't a simpler fix be to test "pwd" here?
>         if (!pwd)
>                 free(password);
>         return pwd;
> 

The problem is on success, when 'pwd' is actually not NULL.
With that, I can't free(password). I would need to asprintf(pwd, ...) or
strndup(password). Because of that, I thought it would be cleaner to
remove 'password' completely.

Your call ... :)

> thanks,
> 
> Mimi
> 
> >  }
> >  
> >  int main(int argc, char *argv[])
> 
> 

-- 
bmeneg 
PGP Key: http://bmeneg.com/pubkey.txt

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