Re: [PATCH] libsemanage: direct_api: clamp write length in ERR_CHLD_STDERR()

On Wed, Jul 15, 2026 at 3:23 PM Stephen Smalley
<[email protected]> wrote:
>
> snprintf() returns the number of bytes it would have written on
> truncation, which can exceed the buffer size, and can potentially
> return < 0 on other error conditions. Clamp the write length to the
> buffer size less the terminator and only write if snprintf() actually
> wrote bytes to the buffer.
>
> Signed-off-by: Stephen Smalley <[email protected]>

Merged.

> ---
>  libsemanage/src/direct_api.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/libsemanage/src/direct_api.c b/libsemanage/src/direct_api.c
> index b87b87e7..6c84b23c 100644
> --- a/libsemanage/src/direct_api.c
> +++ b/libsemanage/src/direct_api.c
> @@ -618,11 +618,19 @@ static int read_from_pipe_to_data(semanage_handle_t *sh, size_t initial_len,
>                                   "libsemanage.semanage_pipe_data: ",          \
>                                   strlen("libsemanage.semanage_pipe_data: ")); \
>                 n = snprintf(buf, sizeof(buf), __VA_ARGS__);                   \
> -               (void)!write_full(err_fd[PIPE_WRITE], buf, n);                 \
> +               if (n > 0) {                                                   \
> +                       if ((size_t)n >= sizeof(buf))                          \
> +                               n = sizeof(buf) - 1;                           \
> +                       (void)!write_full(err_fd[PIPE_WRITE], buf, (size_t)n); \
> +               }                                                              \
>                 if (errsv) {                                                   \
>                         errno = errsv;                                         \
>                         n = snprintf(buf, sizeof(buf), " (%m).");              \
> -                       (void)!write_full(err_fd[PIPE_WRITE], buf, n);         \
> +                       if (n > 0) {                                           \
> +                               if ((size_t)n >= sizeof(buf))                  \
> +                                       n = sizeof(buf) - 1;                   \
> +                               (void)!write_full(err_fd[PIPE_WRITE], buf, n); \
> +                       }                                                      \
>                 }                                                              \
>                 (void)!write_full(err_fd[PIPE_WRITE], "\n", strlen("\n"));     \
>                 (void)!fsync(err_fd[PIPE_WRITE]);                              \
> --
> 2.55.0
>