kernel: backport fix for a page pool related race condition
Signed-off-by: Felix Fietkau <nbd@nbd.name>
This commit is contained in:
Felix Fietkau
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From: Liang Chen <liangchen.linux@gmail.com>
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Date: Thu, 13 Apr 2023 17:03:53 +0800
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Subject: [PATCH] skbuff: Fix a race between coalescing and releasing SKBs
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Commit 1effe8ca4e34 ("skbuff: fix coalescing for page_pool fragment
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recycling") allowed coalescing to proceed with non page pool page and page
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pool page when @from is cloned, i.e.
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to->pp_recycle --> false
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from->pp_recycle --> true
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skb_cloned(from) --> true
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However, it actually requires skb_cloned(@from) to hold true until
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coalescing finishes in this situation. If the other cloned SKB is
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released while the merging is in process, from_shinfo->nr_frags will be
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set to 0 toward the end of the function, causing the increment of frag
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page _refcount to be unexpectedly skipped resulting in inconsistent
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reference counts. Later when SKB(@to) is released, it frees the page
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directly even though the page pool page is still in use, leading to
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use-after-free or double-free errors. So it should be prohibited.
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The double-free error message below prompted us to investigate:
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BUG: Bad page state in process swapper/1 pfn:0e0d1
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page:00000000c6548b28 refcount:-1 mapcount:0 mapping:0000000000000000
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index:0x2 pfn:0xe0d1
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flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff)
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raw: 000fffffc0000000 0000000000000000 ffffffff00000101 0000000000000000
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raw: 0000000000000002 0000000000000000 ffffffffffffffff 0000000000000000
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page dumped because: nonzero _refcount
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CPU: 1 PID: 0 Comm: swapper/1 Tainted: G E 6.2.0+
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Call Trace:
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<IRQ>
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dump_stack_lvl+0x32/0x50
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bad_page+0x69/0xf0
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free_pcp_prepare+0x260/0x2f0
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free_unref_page+0x20/0x1c0
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skb_release_data+0x10b/0x1a0
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napi_consume_skb+0x56/0x150
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net_rx_action+0xf0/0x350
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? __napi_schedule+0x79/0x90
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__do_softirq+0xc8/0x2b1
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__irq_exit_rcu+0xb9/0xf0
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common_interrupt+0x82/0xa0
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</IRQ>
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<TASK>
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asm_common_interrupt+0x22/0x40
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RIP: 0010:default_idle+0xb/0x20
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Fixes: 53e0961da1c7 ("page_pool: add frag page recycling support in page pool")
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Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
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Reviewed-by: Eric Dumazet <edumazet@google.com>
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Link: https://lore.kernel.org/r/20230413090353.14448-1-liangchen.linux@gmail.com
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Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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---
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--- a/net/core/skbuff.c
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+++ b/net/core/skbuff.c
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@@ -5208,18 +5208,18 @@ bool skb_try_coalesce(struct sk_buff *to
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if (skb_cloned(to))
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return false;
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- /* In general, avoid mixing slab allocated and page_pool allocated
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- * pages within the same SKB. However when @to is not pp_recycle and
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- * @from is cloned, we can transition frag pages from page_pool to
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- * reference counted.
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- *
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- * On the other hand, don't allow coalescing two pp_recycle SKBs if
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- * @from is cloned, in case the SKB is using page_pool fragment
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+ /* In general, avoid mixing page_pool and non-page_pool allocated
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+ * pages within the same SKB. Additionally avoid dealing with clones
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+ * with page_pool pages, in case the SKB is using page_pool fragment
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* references (PP_FLAG_PAGE_FRAG). Since we only take full page
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* references for cloned SKBs at the moment that would result in
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* inconsistent reference counts.
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+ * In theory we could take full references if @from is cloned and
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+ * !@to->pp_recycle but its tricky (due to potential race with
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+ * the clone disappearing) and rare, so not worth dealing with.
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*/
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- if (to->pp_recycle != (from->pp_recycle && !skb_cloned(from)))
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+ if (to->pp_recycle != from->pp_recycle ||
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+ (from->pp_recycle && skb_cloned(from)))
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return false;
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if (len <= skb_tailroom(to)) {
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@ -0,0 +1,85 @@
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From: Liang Chen <liangchen.linux@gmail.com>
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Date: Thu, 13 Apr 2023 17:03:53 +0800
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Subject: [PATCH] skbuff: Fix a race between coalescing and releasing SKBs
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Commit 1effe8ca4e34 ("skbuff: fix coalescing for page_pool fragment
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recycling") allowed coalescing to proceed with non page pool page and page
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pool page when @from is cloned, i.e.
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to->pp_recycle --> false
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from->pp_recycle --> true
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skb_cloned(from) --> true
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However, it actually requires skb_cloned(@from) to hold true until
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coalescing finishes in this situation. If the other cloned SKB is
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released while the merging is in process, from_shinfo->nr_frags will be
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set to 0 toward the end of the function, causing the increment of frag
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page _refcount to be unexpectedly skipped resulting in inconsistent
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reference counts. Later when SKB(@to) is released, it frees the page
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directly even though the page pool page is still in use, leading to
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use-after-free or double-free errors. So it should be prohibited.
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The double-free error message below prompted us to investigate:
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BUG: Bad page state in process swapper/1 pfn:0e0d1
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page:00000000c6548b28 refcount:-1 mapcount:0 mapping:0000000000000000
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index:0x2 pfn:0xe0d1
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flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff)
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raw: 000fffffc0000000 0000000000000000 ffffffff00000101 0000000000000000
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raw: 0000000000000002 0000000000000000 ffffffffffffffff 0000000000000000
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page dumped because: nonzero _refcount
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CPU: 1 PID: 0 Comm: swapper/1 Tainted: G E 6.2.0+
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Call Trace:
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<IRQ>
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dump_stack_lvl+0x32/0x50
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bad_page+0x69/0xf0
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free_pcp_prepare+0x260/0x2f0
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free_unref_page+0x20/0x1c0
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skb_release_data+0x10b/0x1a0
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napi_consume_skb+0x56/0x150
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net_rx_action+0xf0/0x350
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? __napi_schedule+0x79/0x90
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__do_softirq+0xc8/0x2b1
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__irq_exit_rcu+0xb9/0xf0
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common_interrupt+0x82/0xa0
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</IRQ>
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<TASK>
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asm_common_interrupt+0x22/0x40
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RIP: 0010:default_idle+0xb/0x20
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Fixes: 53e0961da1c7 ("page_pool: add frag page recycling support in page pool")
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Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
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Reviewed-by: Eric Dumazet <edumazet@google.com>
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Link: https://lore.kernel.org/r/20230413090353.14448-1-liangchen.linux@gmail.com
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Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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---
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--- a/net/core/skbuff.c
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+++ b/net/core/skbuff.c
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@@ -5397,18 +5397,18 @@ bool skb_try_coalesce(struct sk_buff *to
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if (skb_cloned(to))
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return false;
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- /* In general, avoid mixing slab allocated and page_pool allocated
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- * pages within the same SKB. However when @to is not pp_recycle and
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- * @from is cloned, we can transition frag pages from page_pool to
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- * reference counted.
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- *
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- * On the other hand, don't allow coalescing two pp_recycle SKBs if
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- * @from is cloned, in case the SKB is using page_pool fragment
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+ /* In general, avoid mixing page_pool and non-page_pool allocated
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+ * pages within the same SKB. Additionally avoid dealing with clones
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+ * with page_pool pages, in case the SKB is using page_pool fragment
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* references (PP_FLAG_PAGE_FRAG). Since we only take full page
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* references for cloned SKBs at the moment that would result in
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* inconsistent reference counts.
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+ * In theory we could take full references if @from is cloned and
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+ * !@to->pp_recycle but its tricky (due to potential race with
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+ * the clone disappearing) and rare, so not worth dealing with.
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*/
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- if (to->pp_recycle != (from->pp_recycle && !skb_cloned(from)))
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+ if (to->pp_recycle != from->pp_recycle ||
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+ (from->pp_recycle && skb_cloned(from)))
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return false;
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if (len <= skb_tailroom(to)) {
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