On Sat, Jul 07, 2018 at 09:41:03AM +0000, Bernd Edlinger wrote:
> The strncpy causes a warning [-Wstringop-truncation] here,
> which indicates that it never appends a NUL byte to the path.
> The NUL byte is only there because the buffer is allocated
> with kzalloc(PAGE_SIZE, GFP_KERNEL), but since the range-check
> is also off-by-one, and PAGE_SIZE==PATH_MAX the returned string
> will not be zero-terminated if it is exactly PATH_MAX characters.
> Furthermore also the initial loop may theoretically exceed PATH_MAX
> and cause a fault.
>
> Signed-off-by: Bernd Edlinger <bernd.edlin...@hotmail.de>
> ---
> fs/kernfs/symlink.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c
> index 08ccabd..c8b7d44a 100644
> --- a/fs/kernfs/symlink.c
> +++ b/fs/kernfs/symlink.c
> @@ -63,7 +63,10 @@ static int kernfs_get_target_path(struct kernfs_node
> if (base == kn)
> break;
>
> - strcpy(s, "../");
> + if ((s - path) + 3 >= PATH_MAX)
> + return -ENAMETOOLONG;
> +
> + memcpy(s, "../", 3);
> s += 3;
> base = base->parent;
> }
> @@ -79,16 +82,17 @@ static int kernfs_get_target_path(struct kernfs_node
> if (len < 2)
> return -EINVAL;
> len--;
> - if ((s - path) + len > PATH_MAX)
> + if ((s - path) + len >= PATH_MAX)
> return -ENAMETOOLONG;
>
> /* reverse fillup of target string from target to base */
> kn = target;
> + s[len] = '\0';
> while (kn->parent && kn != base) {
> int slen = strlen(kn->name);
>
> len -= slen;
> - strncpy(s + len, kn->name, slen);
> + memcpy(s + len, kn->name, slen);
> if (len)
> s[--len] = '/';
>
This last memcpy replacement has already been applied to my tree, from a
patch from soeone else, so are you sure all of the other changes are
also really needed? Why the extra \0 termination of a string that is
already terminated?
And why is the first memcpy replacement needed? gcc doesn't say
anything about that, does it?
thanks,
greg k-h
