Re: [PATCH] selftests/x86/lam: Zero out buffer for readlink()

[Binbin Wu]

On 9/27/2023 7:02 PM, kirill.shutemov@xxxxxxxxxxxxxxx wrote:
> On Sun, Sep 24, 2023 at 07:33:46AM +0800, Binbin Wu wrote:
> > Zero out the buffer for readlink() since readlink() does not append a
> > terminating null byte to the buffer.
> >
> > Fixes: 833c12ce0f430 ("selftests/x86/lam: Add inherit test cases for linear-address masking")
> >
> > Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
> > ---
> >   tools/testing/selftests/x86/lam.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
> > index eb0e46905bf9..9f06942a8e25 100644
> > --- a/tools/testing/selftests/x86/lam.c
> > +++ b/tools/testing/selftests/x86/lam.c
> > @@ -680,7 +680,7 @@ static int handle_execve(struct testcases *test)
> >   		perror("Fork failed.");
> >   		ret = 1;
> >   	} else if (pid == 0) {
> > -		char path[PATH_MAX];
> > +		char path[PATH_MAX] = {0};
> Shouldn't it be PATH_MAX+1 to handle the case when readlink(2) stores
> exactly PATH_MAX bytes into the buffer?
According to the definition of PATH_MAX in include/uapi/linux/limits.h
#define PATH_MAX        4096    /* # chars in a path name including nul */

IIUC, Linux limits the path length to 4095 and PATH_MAX includes the 
terminating nul.


> >   
> >   		/* Set LAM mode in parent process */
> >   		if (set_lam(lam) != 0)
> >
> > base-commit: ce9ecca0238b140b88f43859b211c9fdfd8e5b70
> > --
> > 2.25.1