Jason Gunthorpe
2022-Jun-28 00:40 UTC
[PATCH][next] treewide: uapi: Replace zero-length arrays with flexible-array members
On Mon, Jun 27, 2022 at 08:27:37PM +0200, Daniel Borkmann wrote:> On 6/27/22 8:04 PM, Gustavo A. R. Silva wrote: > > There is a regular need in the kernel to provide a way to declare > > having a dynamically sized set of trailing elements in a structure. > > Kernel code should always use ?flexible array members?[1] for these > > cases. The older style of one-element or zero-length arrays should > > no longer be used[2]. > > > > This code was transformed with the help of Coccinelle: > > (linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch) > > > > @@ > > identifier S, member, array; > > type T1, T2; > > @@ > > > > struct S { > > ... > > T1 member; > > T2 array[ > > - 0 > > ]; > > }; > > > > -fstrict-flex-arrays=3 is coming and we need to land these changes > > to prevent issues like these in the short future: > > > > ../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0, > > but the source string has length 2 (including NUL byte) [-Wfortify-source] > > strcpy(de3->name, "."); > > ^ > > > > Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If > > this breaks anything, we can use a union with a new member name. > > > > [1] https://en.wikipedia.org/wiki/Flexible_array_member > > [2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays > > > > Link: https://github.com/KSPP/linux/issues/78 > > Build-tested-by: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp at intel.com/ > > Signed-off-by: Gustavo A. R. Silva <gustavoars at kernel.org> > > --- > > Hi all! > > > > JFYI: I'm adding this to my -next tree. :) > > Fyi, this breaks BPF CI: > > https://github.com/kernel-patches/bpf/runs/7078719372?check_suite_focus=true > > [...] > progs/map_ptr_kern.c:314:26: error: field 'trie_key' with variable sized type 'struct bpf_lpm_trie_key' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > struct bpf_lpm_trie_key trie_key; > ^This will break the rdma-core userspace as well, with a similar error: /usr/bin/clang-13 -DVERBS_DEBUG -Dibverbs_EXPORTS -Iinclude -I/usr/include/libnl3 -I/usr/include/drm -g -O2 -fdebug-prefix-map=/__w/1/s=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -Wmissing-prototypes -Wmissing-declarations -Wwrite-strings -Wformat=2 -Wcast-function-type -Wformat-nonliteral -Wdate-time -Wnested-externs -Wshadow -Wstrict-prototypes -Wold-style-definition -Werror -Wredundant-decls -g -fPIC -std=gnu11 -MD -MT libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o -MF libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o.d -o libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o -c ../libibverbs/cmd_flow.c In file included from ../libibverbs/cmd_flow.c:33: In file included from include/infiniband/cmd_write.h:36: In file included from include/infiniband/cmd_ioctl.h:41: In file included from include/infiniband/verbs.h:48: In file included from include/infiniband/verbs_api.h:66: In file included from include/infiniband/ib_user_ioctl_verbs.h:38: include/rdma/ib_user_verbs.h:436:34: error: field 'base' with variable sized type 'struct ib_uverbs_create_cq_resp' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] struct ib_uverbs_create_cq_resp base; ^ include/rdma/ib_user_verbs.h:644:34: error: field 'base' with variable sized type 'struct ib_uverbs_create_qp_resp' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] struct ib_uverbs_create_qp_resp base; Which is why I gave up trying to change these.. Though maybe we could just switch off -Wgnu-variable-sized-type-not-at-end during configuration ? Jason
Kees Cook
2022-Jun-28 17:54 UTC
[PATCH][next] treewide: uapi: Replace zero-length arrays with flexible-array members
On Mon, Jun 27, 2022 at 09:40:52PM -0300, Jason Gunthorpe wrote:> On Mon, Jun 27, 2022 at 08:27:37PM +0200, Daniel Borkmann wrote: > > [...] > > Fyi, this breaks BPF CI: > > > > https://github.com/kernel-patches/bpf/runs/7078719372?check_suite_focus=true > > > > [...] > > progs/map_ptr_kern.c:314:26: error: field 'trie_key' with variable sized type 'struct bpf_lpm_trie_key' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > struct bpf_lpm_trie_key trie_key; > > ^The issue here seems to be a collision between "unknown array size" and known sizes: struct bpf_lpm_trie_key { __u32 prefixlen; /* up to 32 for AF_INET, 128 for AF_INET6 */ __u8 data[0]; /* Arbitrary size */ }; struct lpm_key { struct bpf_lpm_trie_key trie_key; __u32 data; }; This is treating trie_key as a header, which it's not: it's a complete structure. :) Perhaps: struct lpm_key { __u32 prefixlen; __u32 data; }; I don't see anything else trying to include bpf_lpm_trie_key.> > This will break the rdma-core userspace as well, with a similar > error: > > /usr/bin/clang-13 -DVERBS_DEBUG -Dibverbs_EXPORTS -Iinclude -I/usr/include/libnl3 -I/usr/include/drm -g -O2 -fdebug-prefix-map=/__w/1/s=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -Wmissing-prototypes -Wmissing-declarations -Wwrite-strings -Wformat=2 -Wcast-function-type -Wformat-nonliteral -Wdate-time -Wnested-externs -Wshadow -Wstrict-prototypes -Wold-style-definition -Werror -Wredundant-decls -g -fPIC -std=gnu11 -MD -MT libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o -MF libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o.d -o libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o -c ../libibverbs/cmd_flow.c > In file included from ../libibverbs/cmd_flow.c:33: > In file included from include/infiniband/cmd_write.h:36: > In file included from include/infiniband/cmd_ioctl.h:41: > In file included from include/infiniband/verbs.h:48: > In file included from include/infiniband/verbs_api.h:66: > In file included from include/infiniband/ib_user_ioctl_verbs.h:38: > include/rdma/ib_user_verbs.h:436:34: error: field 'base' with variable sized type 'struct ib_uverbs_create_cq_resp' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > struct ib_uverbs_create_cq_resp base; > ^ > include/rdma/ib_user_verbs.h:644:34: error: field 'base' with variable sized type 'struct ib_uverbs_create_qp_resp' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > struct ib_uverbs_create_qp_resp base;This looks very similar, a struct of unknown size is being treated as a header struct: struct ib_uverbs_create_cq_resp { __u32 cq_handle; __u32 cqe; __aligned_u64 driver_data[0]; }; struct ib_uverbs_ex_create_cq_resp { struct ib_uverbs_create_cq_resp base; __u32 comp_mask; __u32 response_length; }; And it only gets used here: DECLARE_UVERBS_WRITE(IB_USER_VERBS_CMD_CREATE_CQ, ib_uverbs_create_cq, UAPI_DEF_WRITE_UDATA_IO( struct ib_uverbs_create_cq, struct ib_uverbs_create_cq_resp), ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ UAPI_DEF_METHOD_NEEDS_FN(create_cq)), which must also be assuming it's a header. So probably better to just drop the driver_data field? I don't see anything using it (that I can find) besides as a sanity-check that the field exists and is at the end of the struct. -- Kees Cook