CVE-2022-48847

In the Linux kernel, the following vulnerability has been resolved:

watch_queue: Fix filter limit check

In watchqueuesetfilter(), there are a couple of places where we check that the filter type value does not exceed what the typefilter bitmap can hold. One place calculates the number of bits by:

if (tf[i].type >= sizeof(wfilter->type_filter) * 8)

which is fine, but the second does:

if (tf[i].type >= sizeof(wfilter->typefilter) * BITSPER_LONG)

which is not. This can lead to a couple of out-of-bounds writes due to a too-large type:

(1) __setbit() on wfilter->typefilter (2) Writing more elements in wfilter->filters[] than we allocated.

Fix this by just using the proper WATCHTYPE_NR instead, which is the number of types we actually know about.

The bug may cause an oops looking something like:

BUG: KASAN: slab-out-of-bounds in watchqueuesetfilter+0x659/0x740 Write of size 4 at addr ffff88800d2c66bc by task watchqueueoob/611 ... Call Trace: <TASK> dumpstacklvl+0x45/0x59 printaddressdescription.constprop.0+0x1f/0x150 ... kasanreport.cold+0x7f/0x11b ... watchqueueset_filter+0x659/0x740 ... __x64sysioctl+0x127/0x190 dosyscall64+0x43/0x90 entrySYSCALL64afterhwframe+0x44/0xae

Allocated by task 611: kasansavestack+0x1e/0x40 __kasankmalloc+0x81/0xa0 watchqueuesetfilter+0x23a/0x740 __x64sysioctl+0x127/0x190 dosyscall64+0x43/0x90 entrySYSCALL64afterhwframe+0x44/0xae

The buggy address belongs to the object at ffff88800d2c66a0 which belongs to the cache kmalloc-32 of size 32 The buggy address is located 28 bytes inside of 32-byte region [ffff88800d2c66a0, ffff88800d2c66c0)