[RFC net v7] net: skb_expand_head() adjust skb->truesize incorrectly
From: Jakub Kicinski <kuba@kernel.org>
Date: 2021-09-17 16:24:28
Subsystem:
networking [general], networking [sockets], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Kuniyuki Iwashima, Willem de Bruijn, Linus Torvalds
From: Vasily Averin <redacted> Christoph Paasch reports [1] about incorrect skb->truesize after skb_expand_head() call in ip6_xmit. This may happen because of two reasons: - skb_set_owner_w() for newly cloned skb is called too early, before pskb_expand_head() where truesize is adjusted for (!skb-sk) case. - pskb_expand_head() does not adjust truesize in (skb->sk) case. In this case sk->sk_wmem_alloc should be adjusted too. Eric cautions us against increasing sk_wmem_alloc if the old skb did not hold any wmem references. [1] https://lkml.org/lkml/2021/8/20/1082 Fixes: f1260ff15a71 ("skbuff: introduce skb_expand_head()") Reported-by: Christoph Paasch <redacted> Reported-by: Hao Sun <redacted> Signed-off-by: Vasily Averin <redacted> Signed-off-by: Jakub Kicinski <kuba@kernel.org> --- v7: - shift more magic into helpers - follow Eric's advice and don't inherit non-wmem sks for now Looks like we stalled here, let me try to push this forward. This builds, is it possible to repro without syzcaller? Anyone willing to test? --- include/net/sock.h | 2 ++ net/core/skbuff.c | 50 +++++++++++++++++++++++++++++++++++----------- net/core/sock.c | 10 ++++++++++ 3 files changed, 50 insertions(+), 12 deletions(-)
diff --git a/include/net/sock.h b/include/net/sock.h
index 66a9a90f9558..102e3e1009d1 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h@@ -1707,6 +1707,8 @@ void sock_pfree(struct sk_buff *skb); #define sock_edemux sock_efree #endif +bool is_skb_wmem(const struct sk_buff *skb); + int sock_setsockopt(struct socket *sock, int level, int op, sockptr_t optval, unsigned int optlen);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7c2ab27fcbf9..5093321c2b65 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c@@ -1786,6 +1786,24 @@ struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom) } EXPORT_SYMBOL(skb_realloc_headroom); +static void skb_owner_inherit(struct sk_buff *nskb, struct sk_buff *oskb) +{ + if (is_skb_wmem(oskb)) + skb_set_owner_w(nskb, oskb->sk); + + /* handle rmem sock etc. as needed .. */ +} + +static void skb_increase_truesize(struct sk_buff *skb, unsigned int add) +{ + if (is_skb_wmem(skb)) + refcount_add(add, &skb->sk->sk_wmem_alloc); + /* handle rmem sock etc. as needed .. */ + WARN_ON(skb->destructor == sock_rfree); + + skb->truesize += add; +} + /** * skb_expand_head - reallocate header of &sk_buff * @skb: buffer to reallocate
@@ -1801,6 +1819,7 @@ EXPORT_SYMBOL(skb_realloc_headroom); struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom) { int delta = headroom - skb_headroom(skb); + int osize = skb_end_offset(skb); if (WARN_ONCE(delta <= 0, "%s is expecting an increase in the headroom", __func__))
@@ -1810,21 +1829,28 @@ struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom) if (skb_shared(skb)) { struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC); - if (likely(nskb)) { - if (skb->sk) - skb_set_owner_w(nskb, skb->sk); - consume_skb(skb); - } else { - kfree_skb(skb); - } + if (unlikely(!nskb)) + goto err_free; + + skb_owner_inherit(nskb, skb); + consume_skb(skb); skb = nskb; } - if (skb && - pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) { - kfree_skb(skb); - skb = NULL; - } + + if (pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) + goto err_free; + delta = skb_end_offset(skb) - osize; + + /* pskb_expand_head() will adjust truesize itself for non-sk cases + * todo: move the adjustment there at some point? + */ + if (skb->sk && skb->destructor != sock_edemux) + skb_increase_truesize(skb, delta); + return skb; +err_free: + kfree_skb(skb); + return NULL; } EXPORT_SYMBOL(skb_expand_head);
diff --git a/net/core/sock.c b/net/core/sock.c
index 62627e868e03..1483b4f755ef 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c@@ -2227,6 +2227,16 @@ void skb_set_owner_w(struct sk_buff *skb, struct sock *sk) } EXPORT_SYMBOL(skb_set_owner_w); +/* Should clones of this skb count towards skb->sk->sk_wmem_alloc + * and use sock_wfree() as their destructor? + */ +bool is_skb_wmem(const struct sk_buff *skb) +{ + return skb->destructor == sock_wfree || + skb->destructor == __sock_wfree || + (IS_ENABLED(CONFIG_INET) && skb->destructor == tcp_wfree); +} + static bool can_skb_orphan_partial(const struct sk_buff *skb) { #ifdef CONFIG_TLS_DEVICE
--
2.31.1