Description
In the Linux kernel, the following vulnerability has been resolved: bpf: NUL-terminate replaced sysctl value When writing to sysctls, proc_sys_call_handler() guarantees that the buffer passed to proc handlers is NUL-terminated. If bpf_sysctl_set_new_value() replaces the pending sysctl value, it can hand a replacement buffer directly to proc handlers. However, the helper currently copies only buf_len bytes into that buffer without appending a NUL terminator, leaving downstream parsers vulnerable to out-of-bounds access. Fix this by appending a '\0' after the replaced value to restore the expected sysctl semantics. Since the helper already rejects buf_len greater than PAGE_SIZE - 1, there is always room for the extra byte. Reproduced in a QEMU x86_64 guest booted with KASAN while exercising the sysctl replacement path with a cgroup/sysctl BPF program. The reproducer targets `/proc/sys/net/core/flow_limit_cpu_bitmap`, fills the original user write buffer with non-zero bytes, and overrides the sysctl value so the replacement buffer lacks a terminating NUL. Under that setup, the pre-fix kernel reported: BUG: KASAN: slab-out-of-bounds in strnchrnul+0x72/0x90 Read of size 1 at addr ffff88800de57000 by task repro_patch3/66 CPU: 0 UID: 0 PID: 66 Comm: repro_patch3 Not tainted 7.1.0-rc3-00269-g8370ca1f87cc #6 PREEMPT(lazy) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x68/0xa0 print_report+0xcb/0x5e0 ? __virt_addr_valid+0x21d/0x3f0 ? strnchrnul+0x72/0x90 ? strnchrnul+0x72/0x90 kasan_report+0xca/0x100 ? strnchrnul+0x72/0x90 strnchrnul+0x72/0x90 bitmap_parse+0x37/0x2e0 flow_limit_cpu_sysctl+0xc6/0x840 ? __pfx_flow_limit_cpu_sysctl+0x10/0x10 ? __kvmalloc_node_noprof+0x5ba/0x870 proc_sys_call_handler+0x31d/0x480 ? __pfx_proc_sys_call_handler+0x10/0x10 ? selinux_file_permission+0x39f/0x500 ? lock_is_held_type+0x9e/0x120 vfs_write+0x98e/0x1000 ... </TASK> The buggy address is located 0 bytes to the right of allocated 4096-byte region [ffff88800de56000, ffff88800de57000) With this fix applied, rerunning the same sysctl-targeted path yields no corresponding KASAN reports.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
Linux Linux
Default version status: unaffected
32927393dc1ccd60fb2bdc05b9e8e88753761469 to < bfcee1f79aaefa90679ad47690107fb7682724ecaffected32927393dc1ccd60fb2bdc05b9e8e88753761469 to < c73e4a04eedc677fe91a736d7a5db45100adba5eaffected32927393dc1ccd60fb2bdc05b9e8e88753761469 to < 36d3e9f62dc2beb9299d3bb6f589cb9e07f773feaffected32927393dc1ccd60fb2bdc05b9e8e88753761469 to < 31377675c3d75603d957c08e338a9ac27e9f6cd5affected32927393dc1ccd60fb2bdc05b9e8e88753761469 to < 76c14b10f50eb0afcc76e244562fa2d8c661e224affected32927393dc1ccd60fb2bdc05b9e8e88753761469 to < 3b2814dd842a565fcf9cc370156e1ba9eae16239affected32927393dc1ccd60fb2bdc05b9e8e88753761469 to < a66e3b5bacf38d6ab29fa05a9754f7a114485605affected
Linux Linux
Default version status: affected
5.8affected0 to < 5.8unaffected5.10.271 to ≤ 5.10.*unaffected5.15.222 to ≤ 5.15.*unaffected6.1.189 to ≤ 6.1.*unaffected6.6.158 to ≤ 6.6.*unaffected6.12.111 to ≤ 6.12.*unaffected6.18.53 to ≤ 6.18.*unaffected7.2 to ≤ *unaffected
References
- https://git.kernel.org/stable/c/bfcee1f79aaefa90679ad47690107fb7682724ec ↗
- https://git.kernel.org/stable/c/c73e4a04eedc677fe91a736d7a5db45100adba5e ↗
- https://git.kernel.org/stable/c/36d3e9f62dc2beb9299d3bb6f589cb9e07f773fe ↗
- https://git.kernel.org/stable/c/31377675c3d75603d957c08e338a9ac27e9f6cd5 ↗
- https://git.kernel.org/stable/c/76c14b10f50eb0afcc76e244562fa2d8c661e224 ↗
- https://git.kernel.org/stable/c/3b2814dd842a565fcf9cc370156e1ba9eae16239 ↗
- https://git.kernel.org/stable/c/a66e3b5bacf38d6ab29fa05a9754f7a114485605 ↗