Re: [PATCH 05/12] perf jitdump: Check snprintf return before computing header size

On Wed, Aug 5, 2026 at 6:31 AM Arnaldo Carvalho de Melo <[email protected]> wrote:
>
> From: Arnaldo Carvalho de Melo <[email protected]>
>
> snprintf() returns the would-have-been length on truncation.  When the
> jitted filename exceeds PATH_MAX, the unclamped 'size' value inflates
> sizeof(event->mmap2.filename) - size into a massive underflow, causing
> the header.size computation to write an oversized header.  The
> subsequent write to 'id = event + header.size - idr_size' then corrupts
> the heap.
>
> Clamp size to PATH_MAX - 1 after snprintf in both jit_repipe_code_load()
> and jit_repipe_code_move().
>
> Fixes: 9b07e27f88b9 ("perf inject: Add jitdump mmap injection support")
> Reported-by: sashiko-bot <[email protected]>
> Cc: Stephane Eranian <[email protected]>
> Assisted-by: Claude:claude-opus-4.6
> Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
> ---
>  tools/perf/util/jitdump.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
> index 078d3304d2b7ebce..fd11e07bf00b7978 100644
> --- a/tools/perf/util/jitdump.c
> +++ b/tools/perf/util/jitdump.c
> @@ -493,6 +493,9 @@ static int jit_repipe_code_load(struct jit_buf_desc *jd, union jr_entry *jr)
>                         jd->dir,
>                         nspid,
>                         count);
> +       /* snprintf returns would-be length on truncation, clamp to buffer */
> +       if (size >= PATH_MAX)
> +               size = PATH_MAX - 1;

Given the recent fixes to reading /proc/pid/maps where it was assumed
the file paths would be limited to PATH_MAX and it turns out that
PATH_MAX doesn't really do that and we had potential buffer overruns
during synthesis, I wonder it would be more intention revealing here
to use "sizeof(event->mmap2.filename)" rather than PATH_MAX. Other
than the constant used, I agree with the change and using PATH_MAX
isn't wrong.

Reviewed-by: Ian Rogers <[email protected]>

Thanks,
Ian

>
>         size++; /* for \0 */
>
> @@ -623,6 +626,9 @@ static int jit_repipe_code_move(struct jit_buf_desc *jd, union jr_entry *jr)
>                  jd->dir,
>                  nspid,
>                  jr->move.code_index);
> +       /* snprintf returns would-be length on truncation, clamp to buffer */
> +       if (size >= PATH_MAX)
> +               size = PATH_MAX - 1;
>
>         size++; /* for \0 */
>
> --
> 2.55.0
>