[PATCH 5.15 093/110] watch_queue: Fix filter limit check

Greg Kroah-Hartman
2022-03-14T12:12:24Z

From: David Howells <dhowells@redhat.com>

commit c993ee0f9f81caf5767a50d1faeba39a0dc82af2 upstream.

In watch_queue_set_filter(), there are a couple of places where we check
that the filter type value does not exceed what the type_filter 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->type_filter) * BITS_PER_LONG)

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

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

Fix this by just using the proper WATCH_TYPE__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 watch_queue_set_filter+0x659/0x740
Write of size 4 at addr ffff88800d2c66bc by task watch_queue_oob/611
...
Call Trace:
<TASK>
dump_stack_lvl+0x45/0x59
print_address_description.constprop.0+0x1f/0x150
...
kasan_report.cold+0x7f/0x11b
...
watch_queue_set_filter+0x659/0x740
...
__x64_sys_ioctl+0x127/0x190
do_syscall_64+0x43/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae

Allocated by task 611:
kasan_save_stack+0x1e/0x40
__kasan_kmalloc+0x81/0xa0
watch_queue_set_filter+0x23a/0x740
__x64_sys_ioctl+0x127/0x190
do_syscall_64+0x43/0x90
entry_SYSCALL_64_after_hwframe+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)

Fixes: c73be61cede5 ("pipe: Add general notification queue support")
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/watch_queue.h | 3 ++-
kernel/watch_queue.c | 4 ++--
2 files changed, 4 insertions(+), 3 deletions(-)

--- a/include/linux/watch_queue.h
+++ b/include/linux/watch_queue.h
@@ -28,7 +28,8 @@ struct watch_type_filter {
struct watch_filter {
union {
struct rcu_head rcu;
- unsigned long type_filter[2]; /* Bitmask of accepted types */
+ /* Bitmask of accepted types */
+ DECLARE_BITMAP(type_filter, WATCH_TYPE__NR);
};
u32 nr_filters; /* Number of filters */
struct watch_type_filter filters[];
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -320,7 +320,7 @@ long watch_queue_set_filter(struct pipe_
tf[i].info_mask & WATCH_INFO_LENGTH)
goto err_filter;
/* Ignore any unknown types */
- if (tf[i].type >= sizeof(wfilter->type_filter) * 8)
+ if (tf[i].type >= WATCH_TYPE__NR)
continue;
nr_filter++;
}
@@ -336,7 +336,7 @@ long watch_queue_set_filter(struct pipe_

q = wfilter->filters;
for (i = 0; i < filter.nr_filters; i++) {
- if (tf[i].type >= sizeof(wfilter->type_filter) * BITS_PER_LONG)
+ if (tf[i].type >= WATCH_TYPE__NR)
continue;

q->type = tf[i].type;