[PATCH v1] misc: fastrpc: avoid duplicate DMA mappings in fastrpc_create_maps()

[Jianping Li <jianping.li@oss.qualcomm.com>]

fastrpc_create_maps() performs map lookup only for buffer
arguments (i < ctx->nbufs) via fastrpc_map_create(). For
arguments beyond this range, no lookup is performed, which
can result in duplicate DMA mappings for the same file
descriptor.

Additionally, if the same file descriptor is passed multiple
times within a single invocation, performing lookups with
reference counting would increment the reference multiple
times, while fastrpc_put_args() would release it only once,
leading to an imbalanced reference count.

Fix this by allowing fastrpc_map_create() to control whether
the lookup should take a reference. For arguments beyond
ctx->nbufs, the lookup is performed without taking a
reference, ensuring that existing mappings are reused
without introducing duplicate DMA mappings or reference
count imbalance.

Fixes: 10df039834f84 ("misc: fastrpc: Skip reference for DMA handles")
Cc: stable@kernel.org
Signed-off-by: Jianping Li <jianping.li@oss.qualcomm.com>
---
 drivers/misc/fastrpc.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index a9b2ae44c06f..2622a1360a65 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -924,9 +924,9 @@ static int fastrpc_map_attach(struct fastrpc_user *fl, int fd,
 }
 
 static int fastrpc_map_create(struct fastrpc_user *fl, int fd,
-			      u64 len, u32 attr, struct fastrpc_map **ppmap)
+			      u64 len, u32 attr, struct fastrpc_map **ppmap, bool take_ref)
 {
-	if (!fastrpc_map_lookup(fl, fd, ppmap, true))
+	if (!fastrpc_map_lookup(fl, fd, ppmap, take_ref))
 		return 0;
 
 	return fastrpc_map_attach(fl, fd, len, attr, ppmap);
@@ -999,23 +999,23 @@ static int fastrpc_create_maps(struct fastrpc_invoke_ctx *ctx)
 	int i, err;
 
 	for (i = 0; i < ctx->nscalars; ++i) {
+		bool take_ref = true;
 
 		if (ctx->args[i].fd == 0 || ctx->args[i].fd == -1 ||
 		    ctx->args[i].length == 0)
 			continue;
 
-		if (i < ctx->nbufs)
-			err = fastrpc_map_create(ctx->fl, ctx->args[i].fd,
-				 ctx->args[i].length, ctx->args[i].attr, &ctx->maps[i]);
-		else
-			err = fastrpc_map_attach(ctx->fl, ctx->args[i].fd,
-				 ctx->args[i].length, ctx->args[i].attr, &ctx->maps[i]);
+		if (i >= ctx->nbufs)
+			take_ref = false;
+
+		err = fastrpc_map_create(ctx->fl, ctx->args[i].fd, ctx->args[i].length,
+			 ctx->args[i].attr, &ctx->maps[i], take_ref);
 		if (err) {
 			dev_err(dev, "Error Creating map %d\n", err);
 			return -EINVAL;
 		}
-
 	}
+
 	return 0;
 }
 
@@ -1508,7 +1508,7 @@ static int fastrpc_init_create_process(struct fastrpc_user *fl,
 	fl->pd = USER_PD;
 
 	if (init.filelen && init.filefd) {
-		err = fastrpc_map_create(fl, init.filefd, init.filelen, 0, &map);
+		err = fastrpc_map_create(fl, init.filefd, init.filelen, 0, &map, true);
 		if (err)
 			goto err;
 	}
@@ -2100,7 +2100,7 @@ static int fastrpc_req_mem_map(struct fastrpc_user *fl, char __user *argp)
 		return -EFAULT;
 
 	/* create SMMU mapping */
-	err = fastrpc_map_create(fl, req.fd, req.length, 0, &map);
+	err = fastrpc_map_create(fl, req.fd, req.length, 0, &map, true);
 	if (err) {
 		dev_err(dev, "failed to map buffer, fd = %d\n", req.fd);
 		return err;
-- 
2.43.0