Both memdup_user() and vmemdup_user() handle allocations that are
regularly used for exploiting use-after-free type confusion flaws in
the kernel (e.g. prctl() PR_SET_VMA_ANON_NAME[1] and setxattr[2][3][4]
respectively).
Since both are designed for contents coming from userspace, it allows
for userspace-controlled allocation sizes. Use a dedicated set of kmalloc
buckets so these allocations do not share caches with the global kmalloc
buckets.
After a fresh boot under Ubuntu 23.10, we can see the caches are already
in active use:
# grep ^memdup /proc/slabinfo
memdup_user-8k 4 4 8192 4 8 : ...
memdup_user-4k 8 8 4096 8 8 : ...
memdup_user-2k 16 16 2048 16 8 : ...
memdup_user-1k 0 0 1024 16 4 : ...
memdup_user-512 0 0 512 16 2 : ...
memdup_user-256 0 0 256 16 1 : ...
memdup_user-128 0 0 128 32 1 : ...
memdup_user-64 256 256 64 64 1 : ...
memdup_user-32 512 512 32 128 1 : ...
memdup_user-16 1024 1024 16 256 1 : ...
memdup_user-8 2048 2048 8 512 1 : ...
memdup_user-192 0 0 192 21 1 : ...
memdup_user-96 168 168 96 42 1 : ...
Link: https://starlabs.sg/blog/2023/07-prctl-anon_vma_name-an-amusing-heap-spray/ [1]
Link: https://duasynt.com/blog/linux-kernel-heap-spray [2]
Link: https://etenal.me/archives/1336 [3]
Link: https://github.com/a13xp0p0v/kernel-hack-drill/blob/master/drill_exploit_uaf.c [4]
Signed-off-by: Kees Cook <[email protected]>
---
Cc: "GONG, Ruiqi" <[email protected]>
Cc: Xiu Jianfeng <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Matteo Rizzo <[email protected]>
Cc: jvoisin <[email protected]>
Cc: [email protected]
---
mm/util.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/mm/util.c b/mm/util.c
index 53f7fc5912bd..f30460c82641 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -198,6 +198,16 @@ char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
}
EXPORT_SYMBOL(kmemdup_nul);
+static kmem_buckets *user_buckets __ro_after_init;
+
+static int __init init_user_buckets(void)
+{
+ user_buckets = kmem_buckets_create("memdup_user", 0, 0, 0, INT_MAX, NULL);
+
+ return 0;
+}
+subsys_initcall(init_user_buckets);
+
/**
* memdup_user - duplicate memory region from user space
*
@@ -211,7 +221,7 @@ void *memdup_user(const void __user *src, size_t len)
{
void *p;
- p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN);
+ p = kmem_buckets_alloc_track_caller(user_buckets, len, GFP_USER | __GFP_NOWARN);
if (!p)
return ERR_PTR(-ENOMEM);
@@ -237,7 +247,7 @@ void *vmemdup_user(const void __user *src, size_t len)
{
void *p;
- p = kvmalloc(len, GFP_USER);
+ p = kmem_buckets_valloc(user_buckets, len, GFP_USER);
if (!p)
return ERR_PTR(-ENOMEM);
--
2.34.1