The msg subsystem is a common target for exploiting[1][2][3][4][5][6] use-after-free type confusion flaws in the kernel for both read and write primitives. Avoid having a user-controlled size cache share the global kmalloc allocator by using a separate set of kmalloc buckets. After a fresh boot under Ubuntu 23.10, we can see the caches are already in use: # grep ^msg_msg /proc/slabinfo msg_msg-8k 0 0 8192 4 8 : ... msg_msg-4k 96 128 4096 8 8 : ... msg_msg-2k 64 64 2048 16 8 : ... msg_msg-1k 64 64 1024 16 4 : ... msg_msg-16 1024 1024 16 256 1 : ... msg_msg-8 0 0 8 512 1 : ... Link: https://blog.hacktivesecurity.com/index.php/2022/06/13/linux-kernel-exploit-development-1day-case-study/ [1] Link: https://hardenedvault.net/blog/2022-11-13-msg_msg-recon-mitigation-ved/ [2] Link: https://www.willsroot.io/2021/08/corctf-2021-fire-of-salvation-writeup.html [3] Link: https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html [4] Link: https://google.github.io/security-research/pocs/linux/cve-2021-22555/writeup.html [5] Link: https://zplin.me/papers/ELOISE.pdf [6] Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- --- ipc/msgutil.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/ipc/msgutil.c b/ipc/msgutil.c index d0a0e877cadd..36f1aa9ea1cf 100644 --- a/ipc/msgutil.c +++ b/ipc/msgutil.c @@ -42,6 +42,15 @@ struct msg_msgseg { #define DATALEN_MSG ((size_t)PAGE_SIZE-sizeof(struct msg_msg)) #define DATALEN_SEG ((size_t)PAGE_SIZE-sizeof(struct msg_msgseg)) +static struct kmem_buckets *msg_buckets __ro_after_init; + +static int __init init_msg_buckets(void) +{ + msg_buckets = kmem_buckets_create("msg_msg", 0, SLAB_ACCOUNT, 0, 0, NULL); + + return 0; +} +subsys_initcall(init_msg_buckets); static struct msg_msg *alloc_msg(size_t len) { @@ -50,7 +59,7 @@ static struct msg_msg *alloc_msg(size_t len) size_t alen; alen = min(len, DATALEN_MSG); - msg = kmalloc(sizeof(*msg) + alen, GFP_KERNEL_ACCOUNT); + msg = kmem_buckets_alloc(msg_buckets, sizeof(*msg) + alen, GFP_KERNEL); if (msg == NULL) return NULL; -- 2.34.1
