[PATCH v2] misc: fastrpc: validate overlap-derived invoke buffer ranges

[Pengpeng Hou]

fastrpc_get_args() derives rpra[i].buf.pv from the overlap offset that
was computed from user-controlled argument pointers and lengths. The
resulting destination pointer is later passed to copy_from_user() or
memcpy() without checking that the overlap-adjusted range still stays
inside the allocated invoke buffer.

Reject overlap-derived destinations that would point before the start of
the invoke buffer or that would extend past the end of the allocated
packet before storing rpra[i].buf.pv and before copying inline
arguments into the buffer.

Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
Found by static code analysis.
Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
v2:
- add the missing Signed-off-by line
- add a Fixes tag and note that the issue was found by static code analysis
- run checkpatch and keep the patch checkpatch-clean

 drivers/misc/fastrpc.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 47356a5d5804..7dfb5eb6dc92 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -993,6 +993,7 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 	u64 len, rlen, pkt_size;
 	u64 pg_start, pg_end;
 	uintptr_t args;
+	uintptr_t buf_start, buf_end;
 	int metalen;
 
 	inbufs = REMOTE_SCALARS_INBUFS(ctx->sc);
@@ -1016,6 +1017,8 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 	rpra = ctx->buf->virt;
 	list = fastrpc_invoke_buf_start(rpra, ctx->nscalars);
 	pages = fastrpc_phy_page_start(list, ctx->nscalars);
+	buf_start = (uintptr_t)ctx->buf->virt;
+	buf_end = buf_start + pkt_size;
 	args = (uintptr_t)ctx->buf->virt + metalen;
 	rlen = pkt_size - metalen;
 	ctx->rpra = rpra;
@@ -1053,6 +1056,7 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 			pages[i].size = (pg_end - pg_start + 1) * PAGE_SIZE;
 
 		} else {
+			uintptr_t dst;
 
 			if (ctx->olaps[oix].offset == 0) {
 				rlen -= ALIGN(args, FASTRPC_ALIGN) - args;
@@ -1064,7 +1068,18 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 			if (rlen < mlen)
 				goto bail;
 
-			rpra[i].buf.pv = args - ctx->olaps[oix].offset;
+			if (ctx->olaps[oix].offset > args - buf_start) {
+				err = -EINVAL;
+				goto bail;
+			}
+
+			dst = args - ctx->olaps[oix].offset;
+			if (len > buf_end - dst) {
+				err = -EINVAL;
+				goto bail;
+			}
+
+			rpra[i].buf.pv = dst;
 			pages[i].addr = ctx->buf->dma_addr -
 					ctx->olaps[oix].offset +
 					(pkt_size - rlen);
-- 
2.50.1 (Apple Git-155)