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Subject[PATCH v1 3/4] ipc: Check permissions for checkpoint_restart sysctls at open time
Date
As Eric Biederman pointed out, it is possible not to use a custom
proc_handler and check permissions for every write, but to use a
.permission handler. That will allow the checkpoint_restart sysctls to
perform all of their permission checks at open time, and not need any
other special code.

Link: https://lore.kernel.org/lkml/87czib9g38.fsf@email.froward.int.ebiederm.org/
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Alexey Gladkov <legion@kernel.org>
---
ipc/ipc_sysctl.c | 54 ++++++++++++++++++++++++++----------------------
1 file changed, 29 insertions(+), 25 deletions(-)

diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index ff99d0305a5b..5a58598d48c8 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -68,25 +68,6 @@ static int proc_ipc_sem_dointvec(struct ctl_table *table, int write,
return ret;
}

-#ifdef CONFIG_CHECKPOINT_RESTORE
-static int proc_ipc_dointvec_minmax_checkpoint_restore(struct ctl_table *table,
- int write, void *buffer, size_t *lenp, loff_t *ppos)
-{
- struct ipc_namespace *ns = current->nsproxy->ipc_ns;
- struct ctl_table ipc_table;
-
- if (write && !checkpoint_restore_ns_capable(ns->user_ns))
- return -EPERM;
-
- memcpy(&ipc_table, table, sizeof(ipc_table));
-
- ipc_table.extra1 = SYSCTL_ZERO;
- ipc_table.extra2 = SYSCTL_INT_MAX;
-
- return proc_dointvec_minmax(&ipc_table, write, buffer, lenp, ppos);
-}
-#endif
-
int ipc_mni = IPCMNI;
int ipc_mni_shift = IPCMNI_SHIFT;
int ipc_min_cycle = RADIX_TREE_MAP_SIZE;
@@ -172,22 +153,28 @@ static struct ctl_table ipc_sysctls[] = {
.procname = "sem_next_id",
.data = &init_ipc_ns.ids[IPC_SEM_IDS].next_id,
.maxlen = sizeof(init_ipc_ns.ids[IPC_SEM_IDS].next_id),
- .mode = 0666,
- .proc_handler = proc_ipc_dointvec_minmax_checkpoint_restore,
+ .mode = 0444,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_INT_MAX,
},
{
.procname = "msg_next_id",
.data = &init_ipc_ns.ids[IPC_MSG_IDS].next_id,
.maxlen = sizeof(init_ipc_ns.ids[IPC_MSG_IDS].next_id),
- .mode = 0666,
- .proc_handler = proc_ipc_dointvec_minmax_checkpoint_restore,
+ .mode = 0444,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_INT_MAX,
},
{
.procname = "shm_next_id",
.data = &init_ipc_ns.ids[IPC_SHM_IDS].next_id,
.maxlen = sizeof(init_ipc_ns.ids[IPC_SHM_IDS].next_id),
- .mode = 0666,
- .proc_handler = proc_ipc_dointvec_minmax_checkpoint_restore,
+ .mode = 0444,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_INT_MAX,
},
#endif
{}
@@ -203,8 +190,25 @@ static int set_is_seen(struct ctl_table_set *set)
return &current->nsproxy->ipc_ns->ipc_set == set;
}

+static int ipc_permissions(struct ctl_table_header *head, struct ctl_table *table)
+{
+ int mode = table->mode;
+
+#ifdef CONFIG_CHECKPOINT_RESTORE
+ struct ipc_namespace *ns = current->nsproxy->ipc_ns;
+
+ if (((table->data == &ns->ids[IPC_SEM_IDS].next_id) ||
+ (table->data == &ns->ids[IPC_MSG_IDS].next_id) ||
+ (table->data == &ns->ids[IPC_SHM_IDS].next_id)) &&
+ checkpoint_restore_ns_capable(ns->user_ns))
+ mode = 0666;
+#endif
+ return mode;
+}
+
static struct ctl_table_root set_root = {
.lookup = set_lookup,
+ .permissions = ipc_permissions,
};

bool setup_ipc_sysctls(struct ipc_namespace *ns)
--
2.33.2
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