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Message-ID: <202210181110.CD92A00@keescook> Date: Tue, 18 Oct 2022 11:19:40 -0700 From: Kees Cook <keescook@...omium.org> To: sdf@...gle.com Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>, KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] bpf: Use kmalloc_size_roundup() to match ksize() usage On Tue, Oct 18, 2022 at 11:07:38AM -0700, sdf@...gle.com wrote: > On 10/18, Kees Cook wrote: > > Round up allocations with kmalloc_size_roundup() so that the verifier's > > use of ksize() is always accurate and no special handling of the memory > > is needed by KASAN, UBSAN_BOUNDS, nor FORTIFY_SOURCE. Pass the new size > > information back up to callers so they can use the space immediately, > > so array resizing to happen less frequently as well. Explicitly zero > > any trailing bytes in new allocations. > > > Additionally fix a memory allocation leak: if krealloc() fails, "arr" > > wasn't freed, but NULL was return to the caller of realloc_array() would > > be writing NULL to the lvalue, losing the reference to the original > > memory. > > > Cc: Alexei Starovoitov <ast@...nel.org> > > Cc: Daniel Borkmann <daniel@...earbox.net> > > Cc: John Fastabend <john.fastabend@...il.com> > > Cc: Andrii Nakryiko <andrii@...nel.org> > > Cc: Martin KaFai Lau <martin.lau@...ux.dev> > > Cc: Song Liu <song@...nel.org> > > Cc: Yonghong Song <yhs@...com> > > Cc: KP Singh <kpsingh@...nel.org> > > Cc: Stanislav Fomichev <sdf@...gle.com> > > Cc: Hao Luo <haoluo@...gle.com> > > Cc: Jiri Olsa <jolsa@...nel.org> > > Cc: bpf@...r.kernel.org > > Signed-off-by: Kees Cook <keescook@...omium.org> > > --- > > kernel/bpf/verifier.c | 49 +++++++++++++++++++++++++++---------------- > > 1 file changed, 31 insertions(+), 18 deletions(-) > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index 014ee0953dbd..8a0b60207d0e 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -1000,42 +1000,53 @@ static void print_insn_state(struct > > bpf_verifier_env *env, > > */ > > static void *copy_array(void *dst, const void *src, size_t n, size_t > > size, gfp_t flags) > > { > > - size_t bytes; > > + size_t src_bytes, dst_bytes; > > > if (ZERO_OR_NULL_PTR(src)) > > goto out; > > > - if (unlikely(check_mul_overflow(n, size, &bytes))) > > + if (unlikely(check_mul_overflow(n, size, &src_bytes))) > > return NULL; > > > - if (ksize(dst) < bytes) { > > + dst_bytes = kmalloc_size_roundup(src_bytes); > > + if (ksize(dst) < dst_bytes) { > > Why not simply do the following here? > > if (ksize(dst) < ksize(src)) { > > ? Yeah, if src always passes through rounding-up allocation path, that might work. I need to double-check that there isn't a case where "size" makes this go weird -- e.g. a rounded up "src" may be larger than "n * size", but I think that's okay because the memcpy/memset does the right thing. > It seems like we care about src_bytes/bytes only in this case, so maybe > move that check_mul_overflow under this branch as well? > > > > kfree(dst); > > - dst = kmalloc_track_caller(bytes, flags); > > + dst = kmalloc_track_caller(dst_bytes, flags); > > if (!dst) > > return NULL; > > } > > > - memcpy(dst, src, bytes); > > + memcpy(dst, src, src_bytes); > > + memset(dst + src_bytes, 0, dst_bytes - src_bytes); > > out: > > return dst ? dst : ZERO_SIZE_PTR; > > } > > > -/* resize an array from old_n items to new_n items. the array is > > reallocated if it's too > > - * small to hold new_n items. new items are zeroed out if the array > > grows. > > +/* Resize an array from old_n items to *new_n items. The array is > > reallocated if it's too > > + * small to hold *new_n items. New items are zeroed out if the array > > grows. Allocation > > + * is rounded up to next kmalloc bucket size to reduce frequency of > > resizing. *new_n > > + * contains the new total number of items that will fit. > > * > > - * Contrary to krealloc_array, does not free arr if new_n is zero. > > + * Contrary to krealloc, does not free arr if new_n is zero. > > */ > > -static void *realloc_array(void *arr, size_t old_n, size_t new_n, > > size_t size) > > +static void *realloc_array(void *arr, size_t old_n, size_t *new_n, > > size_t size) > > { > > - if (!new_n || old_n == new_n) > > + void *old_arr = arr; > > + size_t alloc_size; > > + > > + if (!new_n || !*new_n || old_n == *new_n) > > goto out; > > > [..] > > > - arr = krealloc_array(arr, new_n, size, GFP_KERNEL); > > - if (!arr) > > + alloc_size = kmalloc_size_roundup(size_mul(*new_n, size)); > > + arr = krealloc(old_arr, alloc_size, GFP_KERNEL); > > + if (!arr) { > > + kfree(old_arr); > > return NULL; > > + } > > Any reason not do hide this complexity behind krealloc_array? Why can't > it take care of those roundup details? It might be possible to do this with a macro, yes, but then callers aren't in a position to take advantage of the new size. Maybe we need something like: arr = krealloc_up(old_arr, alloc_size, &new_size, GFP_KERNEL); Thanks for looking this over! -- Kees Cook
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