Re: [PATCH v3 1/2] coredump: Fixes core_pipe_limit sysctl proc_handler

[Jan Kara]

On Tue 17-12-24 14:29:06, nicolas.bouchinet@xxxxxxxxxxx wrote:
> From: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
> 
> proc_dointvec converts a string to a vector of signed int, which is
> stored in the unsigned int .data core_pipe_limit.
> It was thus authorized to write a negative value to core_pipe_limit
> sysctl which once stored in core_pipe_limit, leads to the signed int
> dump_count check against core_pipe_limit never be true. The same can be
> achieved with core_pipe_limit set to INT_MAX.
> 
> Any negative write or >= to INT_MAX in core_pipe_limit sysctl would
> hypothetically allow a user to create very high load on the system by
> running processes that produces a coredump in case the core_pattern
> sysctl is configured to pipe core files to user space helper.
> Memory or PID exhaustion should happen before but it anyway breaks the
> core_pipe_limit semantic.
> 
> This commit fixes this by changing core_pipe_limit sysctl's proc_handler
> to proc_dointvec_minmax and bound checking between SYSCTL_ZERO and
> SYSCTL_INT_MAX.
> 
> Fixes: a293980c2e26 ("exec: let do_coredump() limit the number of concurrent dumps to pipes")
> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/coredump.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 7f12ff6ad1d3e..c3a74dd194e69 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -1024,7 +1024,9 @@ static struct ctl_table coredump_sysctls[] = {
>  		.data		= &core_pipe_limit,
>  		.maxlen		= sizeof(unsigned int),
>  		.mode		= 0644,
> -		.proc_handler	= proc_dointvec,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= SYSCTL_INT_MAX,
>  	},
>  	{
>  		.procname       = "core_file_note_size_limit",
> -- 
> 2.47.1
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR