From 189b0ddc245139af81198d1a3637cac74f96e13a Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Thu, 26 May 2022 07:34:52 +0100
Subject: [PATCH] pipe: Fix missing lock in pipe_resize_ring()
Git-commit: 189b0ddc245139af81198d1a3637cac74f96e13a
Patch-mainline: v5.19-rc1
References: CVE-2022-2959 bsc#1202681
pipe_resize_ring() needs to take the pipe->rd_wait.lock spinlock to
prevent post_one_notification() from trying to insert into the ring
whilst the ring is being replaced.
The occupancy check must be done after the lock is taken, and the lock
must be taken after the new ring is allocated.
The bug can lead to an oops looking something like:
BUG: KASAN: use-after-free in post_one_notification.isra.0+0x62e/0x840
Read of size 4 at addr ffff88801cc72a70 by task poc/27196
...
Call Trace:
post_one_notification.isra.0+0x62e/0x840
__post_watch_notification+0x3b7/0x650
key_create_or_update+0xb8b/0xd20
__do_sys_add_key+0x175/0x340
__x64_sys_add_key+0xbe/0x140
do_syscall_64+0x5c/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xae
Reported by Selim Enes Karaduman @Enesdex working with Trend Micro Zero
Day Initiative.
Fixes: c73be61cede5 ("pipe: Add general notification queue support")
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-17291
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
fs/pipe.c | 31 ++++++++++++++++++-------------
1 file changed, 18 insertions(+), 13 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c
index e140ea150bbb..11358569a777 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1245,30 +1245,33 @@ unsigned int round_pipe_size(unsigned long size)
/*
* Resize the pipe ring to a number of slots.
+ *
+ * Note the pipe can be reduced in capacity, but only if the current
+ * occupancy doesn't exceed nr_slots; if it does, EBUSY will be
+ * returned instead.
*/
int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
{
struct pipe_buffer *bufs;
unsigned int head, tail, mask, n;
- /*
- * We can shrink the pipe, if arg is greater than the ring occupancy.
- * Since we don't expect a lot of shrink+grow operations, just free and
- * allocate again like we would do for growing. If the pipe currently
- * contains more buffers than arg, then return busy.
- */
- mask = pipe->ring_size - 1;
- head = pipe->head;
- tail = pipe->tail;
- n = pipe_occupancy(pipe->head, pipe->tail);
- if (nr_slots < n)
- return -EBUSY;
-
bufs = kcalloc(nr_slots, sizeof(*bufs),
GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
if (unlikely(!bufs))
return -ENOMEM;
+ spin_lock_irq(&pipe->rd_wait.lock);
+ mask = pipe->ring_size - 1;
+ head = pipe->head;
+ tail = pipe->tail;
+
+ n = pipe_occupancy(head, tail);
+ if (nr_slots < n) {
+ spin_unlock_irq(&pipe->rd_wait.lock);
+ kfree(bufs);
+ return -EBUSY;
+ }
+
/*
* The pipe array wraps around, so just start the new one at zero
* and adjust the indices.
@@ -1300,6 +1303,8 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
pipe->tail = tail;
pipe->head = head;
+ spin_unlock_irq(&pipe->rd_wait.lock);
+
/* This might have made more room for writers */
wake_up_interruptible(&pipe->wr_wait);
return 0;
--
2.35.3