[PATCH] dwfl: fix potential overflow when reporting on kernel modules

[Dmitry V. Levin]

On Thu, Nov 18, 2021 at 07:44:50PM +0000, Matthias Maennich via Elfutils-devel wrote:
> dwfl_linux_kernel_report_modules_ has an outstanding ancient bug when
> reading kernel module information from a modules list file. The target
> buffer for the module name was sized too small to hold potential values.
> Fix that by increasing the value to account for the null termination.
> 
> In practice, this unlikely ever happened, but it now got diagnosed by
> LLVM as part of a stricter -Wfortify-source implementation [1]:
> 
> libdwfl/linux-kernel-modules.c:1019:7: error: 'sscanf' may overflow; destination buffer in argument 3 has size 128, but the corresponding specifier may require size 129 [-Werror,-Wfortify-source]
>                     modname, &modsz, &modaddr) == 3)
> 
> [1] https://github.com/llvm/llvm-project/commit/2db66f8d48beeea835cb9a6940e25bc04ab5d941
> 
> Suggested-by: Paul Pluzhnikov <ppluzhnikov@google.com>
> Signed-off-by: Matthias Maennich <maennich@google.com>
> Change-Id: I97b4fcb536273e5ccc4e37b0b9f0f8ffb7487909
> ---
>  libdwfl/linux-kernel-modules.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libdwfl/linux-kernel-modules.c b/libdwfl/linux-kernel-modules.c
> index c0f8dfa4aef2..58c0c417a597 100644
> --- a/libdwfl/linux-kernel-modules.c
> +++ b/libdwfl/linux-kernel-modules.c
> @@ -1008,7 +1008,7 @@ dwfl_linux_kernel_report_modules (Dwfl *dwfl)
>    int result = 0;
>    Dwarf_Addr modaddr;
>    unsigned long int modsz;
> -  char modname[128];
> +  char modname[128+1];
>    char *line = NULL;
>    size_t linesz = 0;
>    /* We can't just use fscanf here because it's not easy to distinguish \n

LGTM, thanks.


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