* [RFC net] net: skbuff: fix stack variable out of bounds access
@ 2021-03-23 12:52 Arnd Bergmann
2021-03-23 14:42 ` Willem de Bruijn
0 siblings, 1 reply; 4+ messages in thread
From: Arnd Bergmann @ 2021-03-23 12:52 UTC (permalink / raw)
To: David S. Miller, Jakub Kicinski, Willem de Bruijn
Cc: Arnd Bergmann, Alexander Lobakin, Jonathan Lemon, Miaohe Lin,
Guillaume Nault, linux-kernel, netdev
From: Arnd Bergmann <arnd@arndb.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@arndb.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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [RFC net] net: skbuff: fix stack variable out of bounds access
2021-03-23 12:52 [RFC net] net: skbuff: fix stack variable out of bounds access Arnd Bergmann
@ 2021-03-23 14:42 ` Willem de Bruijn
2021-03-23 16:29 ` Arnd Bergmann
0 siblings, 1 reply; 4+ messages in thread
From: Willem de Bruijn @ 2021-03-23 14:42 UTC (permalink / raw)
To: Arnd Bergmann
Cc: David S. Miller, Jakub Kicinski, Arnd Bergmann,
Alexander Lobakin, Jonathan Lemon, Miaohe Lin, Guillaume Nault,
linux-kernel, Network Development
On Tue, Mar 23, 2021 at 8:52 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.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@arndb.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
>
Thanks for addressing this.
A similar fix already landed in 5.12-rc3: commit b228c9b05876 ("net:
expand textsearch ts_state to fit skb_seq_state"). That fix landed in
5.12-rc3.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC net] net: skbuff: fix stack variable out of bounds access
2021-03-23 14:42 ` Willem de Bruijn
@ 2021-03-23 16:29 ` Arnd Bergmann
2021-03-23 17:14 ` Willem de Bruijn
0 siblings, 1 reply; 4+ messages in thread
From: Arnd Bergmann @ 2021-03-23 16:29 UTC (permalink / raw)
To: Willem de Bruijn
Cc: David S. Miller, Jakub Kicinski, Alexander Lobakin,
Jonathan Lemon, Miaohe Lin, Guillaume Nault, linux-kernel,
Network Development
On Tue, Mar 23, 2021 at 3:42 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Tue, Mar 23, 2021 at 8:52 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >>
> A similar fix already landed in 5.12-rc3: commit b228c9b05876 ("net:
> expand textsearch ts_state to fit skb_seq_state"). That fix landed in
> 5.12-rc3.
Ah nice, even the same BUILD_BUG_ON() ;-)
Too bad it had to be found through runtime testing when it could have been
found by the compiler warning.
Arnd
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC net] net: skbuff: fix stack variable out of bounds access
2021-03-23 16:29 ` Arnd Bergmann
@ 2021-03-23 17:14 ` Willem de Bruijn
0 siblings, 0 replies; 4+ messages in thread
From: Willem de Bruijn @ 2021-03-23 17:14 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Willem de Bruijn, David S. Miller, Jakub Kicinski,
Alexander Lobakin, Jonathan Lemon, Miaohe Lin, Guillaume Nault,
linux-kernel, Network Development
On Tue, Mar 23, 2021 at 12:30 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Tue, Mar 23, 2021 at 3:42 PM Willem de Bruijn
> <willemdebruijn.kernel@gmail.com> wrote:
> >
> > On Tue, Mar 23, 2021 at 8:52 AM Arnd Bergmann <arnd@kernel.org> wrote:
> > >>
> > A similar fix already landed in 5.12-rc3: commit b228c9b05876 ("net:
> > expand textsearch ts_state to fit skb_seq_state"). That fix landed in
> > 5.12-rc3.
>
> Ah nice, even the same BUILD_BUG_ON() ;-)
Indeed :) Sorry that your work ended up essentially reproducing that.
> Too bad it had to be found through runtime testing when it could have been
> found by the compiler warning.
Definitely useful. Had I enabled it, it would have saved me a lot of debug time.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-03-23 17:16 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-03-23 12:52 [RFC net] net: skbuff: fix stack variable out of bounds access Arnd Bergmann
2021-03-23 14:42 ` Willem de Bruijn
2021-03-23 16:29 ` Arnd Bergmann
2021-03-23 17:14 ` Willem de Bruijn
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