Waiman Long <longman@xxxxxxxxxx> writes:
> A user can write arbitrary integer values to msgmni and shmmni sysctl
> parameters without getting error, but the actual limit is really
> IPCMNI (32k). This can mislead users as they think they can get a
> value that is not real.
>
> Enforcing the limit by failing the sysctl parameter write, however,
> can break existing user applications.
Which applications examples please.
I am seeing this patchset late but it looks like a whole lot of changes
to avoid a theoretical possibility.
Changes that have an impact on more than just the ipc code you are
patching.
That makes me feel very uncomfortable with these changes.
Eric
> Instead, the range clamping flag
> is set to enforce the limit without failing existing user code. Users
> can easily figure out if the sysctl parameter value is out of range
> by either reading back the parameter value or checking the kernel
> ring buffer for warning.
>
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> ---
> ipc/ipc_sysctl.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
> index 8ad93c2..1955dd4 100644
> --- a/ipc/ipc_sysctl.c
> +++ b/ipc/ipc_sysctl.c
> @@ -99,6 +99,7 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
> static int zero;
> static int one = 1;
> static int int_max = INT_MAX;
> +static int ipc_mni = IPCMNI;
>
> static struct ctl_table ipc_kern_table[] = {
> {
> @@ -120,7 +121,10 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
> .data = &init_ipc_ns.shm_ctlmni,
> .maxlen = sizeof(init_ipc_ns.shm_ctlmni),
> .mode = 0644,
> - .proc_handler = proc_ipc_dointvec,
> + .proc_handler = proc_ipc_dointvec_minmax,
> + .extra1 = &zero,
> + .extra2 = &ipc_mni,
> + .flags = CTL_FLAGS_CLAMP_RANGE,
> },
> {
> .procname = "shm_rmid_forced",
> @@ -147,7 +151,8 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
> .mode = 0644,
> .proc_handler = proc_ipc_dointvec_minmax,
> .extra1 = &zero,
> - .extra2 = &int_max,
> + .extra2 = &ipc_mni,
> + .flags = CTL_FLAGS_CLAMP_RANGE,
> },
> {
> .procname = "auto_msgmni",
