[lttng-dev] [PATCH lttng-tools 01/24] Implement lttng_strncpy safe string copy

[Jérémie Galarneau]

On Mon, May 16, 2016 at 9:42 PM, Mathieu Desnoyers
<mathieu.desnoyers at efficios.com> wrote:
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
>  src/common/macros.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/src/common/macros.h b/src/common/macros.h
> index 308d3d5..6147eff 100644
> --- a/src/common/macros.h
> +++ b/src/common/macros.h
> @@ -20,6 +20,7 @@
>  #define _MACROS_H
>
>  #include <stdlib.h>
> +#include <string.h>
>
>  /*
>   * Takes a pointer x and transform it so we can use it to access members
> @@ -76,4 +77,25 @@ void *zmalloc(size_t len)
>  #define LTTNG_HIDDEN __attribute__((visibility("hidden")))
>  #endif
>
> +/*
> + * lttng_strncpy returns 0 on success, or nonzero on failure.
> + * It checks that the @src string fits into @dest_len before performing
> + * the copy. On failure, no copy has been performed.

Added comment to mention that dest_len includes the NULL delimiter.

> + */
> +static inline
> +int lttng_strncpy(char *dest, const char *src, size_t dest_len)
> +{
> +       if (strlen(src) >= dest_len) {

Switching strlen() to strnlen() to protect against cases such as in
"Fix: illegal memory access in init_ust_event_from_agent_event" where
the source may not be NULL-terminated (even though it should be). I
don't want to change the behavior this close to the release.

A lot of code currently assumes names/identifiers to be bounded by
LTTNG_SYMBOL_NAME_LEN which could cause the strlen() run
to overrun here.

Jérémie

> +               return -1;
> +       }
> +       strncpy(dest, src, dest_len);
> +       /*
> +        * Be extra careful and put final \0 at the end after strncpy(),
> +        * even though we checked the length before. This makes Coverity
> +        * happy.
> +        */
> +       dest[dest_len - 1] = '\0';
> +       return 0;
> +}
> +
>  #endif /* _MACROS_H */
> --
> 2.1.4
>



-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com