| Message ID | 20210323125233.1743957-1-arnd@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | [RFC,net] net: skbuff: fix stack variable out of bounds access | expand |
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.
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
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.
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)); }