xfrm: Update ipcomp_scratches with NULL when freed

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: Update ipcomp_scratches with NULL when freed Currently if ipcomp_alloc_scratches() fails to allocate memory ipcomp_scratches holds obsolete address. So when we try to free the percpu scratches using ipcomp_free_scratches() it tries to vfree non existent vm area. Described below: static void * __percpu *ipcomp_alloc_scratches(void) { ... scratches = alloc_percpu(void *); if (!scratches) return NULL; ipcomp_scratches does not know about this allocation failure. Therefore holding the old obsolete address. ... } So when we free, static void ipcomp_free_scratches(void) { ... scratches = ipcomp_scratches; Assigning obsolete address from ipcomp_scratches if (!scratches) return; for_each_possible_cpu(i) vfree(*per_cpu_ptr(scratches, i)); Trying to free non existent page, causing warning: trying to vfree existent vm area. ... } Fix this breakage by updating ipcomp_scrtches with NULL when scratches is freed

References

• https://git.kernel.org/stable/c/debca61df6bc2f65e020656c9c5b878d6b38d30f
• https://git.kernel.org/stable/c/a39f456d62810c0efb43cead22f98d95b53e4b1a
• https://git.kernel.org/stable/c/1e8abde895b3ac6a368cbdb372e8800c49e73a28
• https://git.kernel.org/stable/c/18373ed500f7cd53e24d9b0bd0f1c09d78dba87e
• https://git.kernel.org/stable/c/be81c44242b20fc3bdcc73480ef8aaee56f5d0b6
• https://git.kernel.org/stable/c/03155680191ef0f004b1d6a5714c5b8cd271ab61
• https://git.kernel.org/stable/c/f3bdba4440d82e0da2b1bfc35d3836c8a8e00677
• https://git.kernel.org/stable/c/2c19945ce8095d065df550e7fe350cd5cc40c6e6
• https://git.kernel.org/stable/c/8a04d2fc700f717104bfb95b0f6694e448a4537f