From: John Fastabend john.fastabend@gmail.com
commit 6562e29cf6f0ddd368657d97a8d484ffc30df5ef upstream.
In the push, pull, and pop helpers operating on skmsg objects to make data writable or insert/remove data we use this bounds check to ensure specified data is valid,
/* Bounds checks: start and pop must be inside message */ if (start >= offset + l || last >= msg->sg.size) return -EINVAL;
The problem here is offset has already included the length of the current element the 'l' above. So start could be past the end of the scatterlist element in the case where start also points into an offset on the last skmsg element.
To fix do the accounting slightly different by adding the length of the previous entry to offset at the start of the iteration. And ensure its initialized to zero so that the first iteration does nothing.
Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface") Fixes: 6fff607e2f14b ("bpf: sk_msg program helper bpf_msg_push_data") Fixes: 7246d8ed4dcce ("bpf: helper to pop data from messages") Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Song Liu songliubraving@fb.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/bpf/20200111061206.8028-5-john.fastabend@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/core/filter.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
--- a/net/core/filter.c +++ b/net/core/filter.c @@ -2231,10 +2231,10 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_ /* First find the starting scatterlist element */ i = msg->sg.start; do { + offset += len; len = sk_msg_elem(msg, i)->length; if (start < offset + len) break; - offset += len; sk_msg_iter_var_next(i); } while (i != msg->sg.end);
@@ -2346,7 +2346,7 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_ u32, len, u64, flags) { struct scatterlist sge, nsge, nnsge, rsge = {0}, *psge; - u32 new, i = 0, l, space, copy = 0, offset = 0; + u32 new, i = 0, l = 0, space, copy = 0, offset = 0; u8 *raw, *to, *from; struct page *page;
@@ -2356,11 +2356,11 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_ /* First find the starting scatterlist element */ i = msg->sg.start; do { + offset += l; l = sk_msg_elem(msg, i)->length;
if (start < offset + l) break; - offset += l; sk_msg_iter_var_next(i); } while (i != msg->sg.end);
@@ -2506,7 +2506,7 @@ static void sk_msg_shift_right(struct sk BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start, u32, len, u64, flags) { - u32 i = 0, l, space, offset = 0; + u32 i = 0, l = 0, space, offset = 0; u64 last = start + len; int pop;
@@ -2516,11 +2516,11 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_m /* First find the starting scatterlist element */ i = msg->sg.start; do { + offset += l; l = sk_msg_elem(msg, i)->length;
if (start < offset + l) break; - offset += l; sk_msg_iter_var_next(i); } while (i != msg->sg.end);