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Message-Id: <20210323125233.1743957-1-arnd@kernel.org>
Date: Tue, 23 Mar 2021 13:52:24 +0100
From: Arnd Bergmann <arnd@...nel.org>
To: "David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Willem de Bruijn <willemb@...gle.com>
Cc: Arnd Bergmann <arnd@...db.de>, Alexander Lobakin <alobakin@...me>,
Jonathan Lemon <jonathan.lemon@...il.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Guillaume Nault <gnault@...hat.com>,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [RFC net] net: skbuff: fix stack variable out of bounds access
From: Arnd Bergmann <arnd@...db.de>
gcc-11 warns that the TS_SKB_CB(&state)) cast in skb_find_text()
leads to an out-of-bounds access in skb_prepare_seq_read() after
the addition of a new struct member made skb_seq_state longer
than ts_state:
net/core/skbuff.c: In function ‘skb_find_text’:
net/core/skbuff.c:3498:26: error: array subscript ‘struct skb_seq_state[0]’ is partly outside array bounds of ‘struct ts_state[1]’ [-Werror=array-bounds]
3498 | st->lower_offset = from;
| ~~~~~~~~~~~~~~~~~^~~~~~
net/core/skbuff.c:3659:25: note: while referencing ‘state’
3659 | struct ts_state state;
| ^~~~~
The warning is currently disabled globally, but I found this
instance during experimental build testing, and it seems
legitimate.
Make the textsearch buffer longer and add a compile-time check to
ensure the two remain the same length.
Fixes: 97550f6fa592 ("net: compound page support in skb_seq_read")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
include/linux/textsearch.h | 2 +-
net/core/skbuff.c | 1 +
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/textsearch.h b/include/linux/textsearch.h
index 13770cfe33ad..6673e4d4ac2e 100644
--- a/include/linux/textsearch.h
+++ b/include/linux/textsearch.h
@@ -23,7 +23,7 @@ struct ts_config;
struct ts_state
{
unsigned int offset;
- char cb[40];
+ char cb[48];
};
/**
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 545a472273a5..dd10d4c5f4bf 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3633,6 +3633,7 @@ static unsigned int skb_ts_get_next_block(unsigned int offset, const u8 **text,
struct ts_config *conf,
struct ts_state *state)
{
+ BUILD_BUG_ON(sizeof(struct skb_seq_state) > sizeof(state->cb));
return skb_seq_read(offset, text, TS_SKB_CB(state));
}
--
2.29.2
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