Commit aa8df3f0 authored by Liang Chen's avatar Liang Chen Committed by Jiantao Xiao
Browse files

skbuff: Fix a race between coalescing and releasing SKBs 

mainline inclusion
from mainline-v6.3-rc7
commit 0646dc31
category: bugfix
bugzilla: https://gitee/com/openeuler/kernel/issues/I718LV
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0646dc31ca886693274df5749cd0c8c1eaaeb5ca



----------------------------------------------------------------------

Commit 1effe8ca ("skbuff: fix coalescing for page_pool fragment
recycling") allowed coalescing to proceed with non page pool page and page
pool page when @from is cloned, i.e.

to->pp_recycle    --> false
from->pp_recycle  --> true
skb_cloned(from)  --> true

However, it actually requires skb_cloned(@from) to hold true until
coalescing finishes in this situation. If the other cloned SKB is
released while the merging is in process, from_shinfo->nr_frags will be
set to 0 toward the end of the function, causing the increment of frag
page _refcount to be unexpectedly skipped resulting in inconsistent
reference counts. Later when SKB(@to) is released, it frees the page
directly even though the page pool page is still in use, leading to
use-after-free or double-free errors. So it should be prohibited.

The double-free error message below prompted us to investigate:
BUG: Bad page state in process swapper/1  pfn:0e0d1
page:00000000c6548b28 refcount:-1 mapcount:0 mapping:0000000000000000
index:0x2 pfn:0xe0d1
flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc0000000 0000000000000000 ffffffff00000101 0000000000000000
raw: 0000000000000002 0000000000000000 ffffffffffffffff 0000000000000000
page dumped because: nonzero _refcount

CPU: 1 PID: 0 Comm: swapper/1 Tainted: G            E      6.2.0+
Call Trace:
 <IRQ>
dump_stack_lvl+0x32/0x50
bad_page+0x69/0xf0
free_pcp_prepare+0x260/0x2f0
free_unref_page+0x20/0x1c0
skb_release_data+0x10b/0x1a0
napi_consume_skb+0x56/0x150
net_rx_action+0xf0/0x350
? __napi_schedule+0x79/0x90
__do_softirq+0xc8/0x2b1
__irq_exit_rcu+0xb9/0xf0
common_interrupt+0x82/0xa0
</IRQ>
<TASK>
asm_common_interrupt+0x22/0x40
RIP: 0010:default_idle+0xb/0x20

Fixes: 53e0961d ("page_pool: add frag page recycling support in page pool")
Signed-off-by: default avatarLiang Chen <liangchen.linux@gmail.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230413090353.14448-1-liangchen.linux@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
Signed-off-by: default avatarJiantao Xiao <xiaojiantao1@h-partners.com>
parent 139aa37a

net/core/skbuff.c

+8 −8
Original line number Diff line number Diff line
@@ -5261,18 +5261,18 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from, 
	if (skb_cloned(to))

		return false;



	/* In general, avoid mixing slab allocated and page_pool allocated

	 * pages within the same SKB. However when @to is not pp_recycle and

	 * @from is cloned, we can transition frag pages from page_pool to

	 * reference counted.

	 *

	 * On the other hand, don't allow coalescing two pp_recycle SKBs if

	 * @from is cloned, in case the SKB is using page_pool fragment

	/* In general, avoid mixing page_pool and non-page_pool allocated

	 * pages within the same SKB. Additionally avoid dealing with clones

	 * with page_pool pages, in case the SKB is using page_pool fragment

	 * references (PP_FLAG_PAGE_FRAG). Since we only take full page

	 * references for cloned SKBs at the moment that would result in

	 * inconsistent reference counts.

	 * In theory we could take full references if @from is cloned and

	 * !@to->pp_recycle but its tricky (due to potential race with

	 * the clone disappearing) and rare, so not worth dealing with.

	 */

	if (to->pp_recycle != (from->pp_recycle && !skb_cloned(from)))

	if (to->pp_recycle != from->pp_recycle ||

	    (from->pp_recycle && skb_cloned(from)))

		return false;



	if (len <= skb_tailroom(to)) {