On Mon, Aug 05, 2024 at 11:39:34AM +0200, Thomas Weißschuh wrote:
Adapt the internal and external APIs of the sysctl core to handle read-only instances of "struct ctl_table".
Finally getting around to this. Testing for this has been done on sysctl-testing base:v6.11-rc6 and now on base:v6.12-rc2. Putting this in sysctl-next so it will get further testing on its way to v6.13. First patch (bugfix) will be ignored as it is already upstream.
Best
Patch 1: Bugfix for the sysctl core, the bug can be reliably triggered with the series applied Patch 2: Trivial preparation commit for the sysctl BPF hook Patch 3: Adapts the internal sysctl APIs Patch 4: Adapts the external sysctl APIs Patch 5: Constifies the sysctl internal tables as proof that it works Patch 6: Updates scripts/const_structs.checkpatch for "struct ctl_table"
Motivation
Moving structures containing function pointers into unmodifiable .rodata prevents attackers or bugs from corrupting and diverting those pointers.
Also the "struct ctl_table" exposed by the sysctl core were never meant to be mutated by users.
For this goal changes to both the sysctl core and "const" qualifiers for various sysctl APIs are necessary.
Full Process
- Drop ctl_table modifications from the sysctl core ([0], in mainline)
- Constify arguments to ctl_table_root::{set_ownership,permissions} ([1], in mainline)
- Migrate users of "ctl_table_header::ctl_table_arg" to "const". (in mainline)
- Afterwards convert "ctl_table_header::ctl_table_arg" itself to const. (in mainline)
- Prepare helpers used to implement proc_handlers throughout the tree to use "const struct ctl_table *". ([2], in mainline)
- Afterwards switch over all proc_handlers callbacks to use "const struct ctl_table *" in one commit. (in mainline)
- Switch over the internals of the sysctl core to "const struct ctl_table *" (this series)
- Switch include/linux/sysctl.h to "const struct ctl_table *" (this series)
- Transition instances of "struct ctl_table" through the tree to const (to be done)
This series is meant to be applied through the sysctl tree.
Signed-off-by: Thomas Weißschuh linux@weissschuh.net
Changes in v2:
- Avoid spurious permanent empty tables (patch 1)
- Link to v1: https://lore.kernel.org/r/20240729-sysctl-const-api-v1-0-ca628c7a942c@weisss...
Thomas Weißschuh (6): sysctl: avoid spurious permanent empty tables bpf: Constify ctl_table argument of filter function sysctl: move internal interfaces to const struct ctl_table sysctl: allow registration of const struct ctl_table sysctl: make internal ctl_tables const const_structs.checkpatch: add ctl_table
fs/proc/internal.h | 2 +- fs/proc/proc_sysctl.c | 100 +++++++++++++++++++++------------------ include/linux/bpf-cgroup.h | 2 +- include/linux/sysctl.h | 12 ++--- kernel/bpf/cgroup.c | 2 +- scripts/const_structs.checkpatch | 1 + 6 files changed, 63 insertions(+), 56 deletions(-)
base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b change-id: 20240729-sysctl-const-api-73954f3d62c1
Best regards,
Thomas Weißschuh linux@weissschuh.net