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watch_queue: Fix filter limit check

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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: c73be61ced ("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>
This commit is contained in:
David Howells 2022-03-11 13:23:31 +00:00 committed by Linus Torvalds
parent ffb217a13a
commit c993ee0f9f
2 changed files with 4 additions and 3 deletions
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3
include/linux/watch_queue.h
View File

@ -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[];

4
kernel/watch_queue.c
View File

@ -320,7 +320,7 @@ long watch_queue_set_filter(struct pipe_inode_info *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_inode_info *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;