On Tue, Mar 23, 2021 at 8:52 AM Arnd Bergmann <a...@kernel.org> wrote:
>
> From: Arnd Bergmann <a...@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 <a...@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.
