[PATCH 3/3] io_uring/zcrx: fix resource leak and double-free hazard in io_import_umem

[KobaK <kobak@nvidia.com>]

From: Koba Ko <kobak@nvidia.com>

io_import_umem() has two problems:

1. When io_account_mem() fails, the function returns an error but leaves
   live pinned pages and sg_table in the mem struct without cleaning them
   up. The caller happens to handle this today via io_zcrx_free_area() ->
   io_release_area_mem(), but the contract is fragile.

2. io_release_area_mem() doesn't NULL out mem->pages after kvfree(),
   making it unsafe to call twice. Since io_zcrx_free_area() always
   calls it during teardown, any earlier cleanup call would cause a
   double-free.

Fix both: populate mem fields before io_account_mem() so
io_release_area_mem() can do a proper cleanup on failure, and add
mem->pages = NULL in io_release_area_mem() to make it idempotent.

Fixes: 262ab205180d2 ("io_uring/zcrx: account area memory")
Signed-off-by: Koba Ko <kobak@nvidia.com>
---
 io_uring/zcrx.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index 62d693287457f..c9ed1139c7bcd 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -188,6 +188,8 @@ static unsigned long io_count_account_pages(struct page **pages, unsigned nr_pag
 	return res;
 }
 
+static void io_release_area_mem(struct io_zcrx_mem *mem);
+
 static int io_import_umem(struct io_zcrx_ifq *ifq,
 			  struct io_zcrx_mem *mem,
 			  struct io_uring_zcrx_area_reg *area_reg)
@@ -213,16 +215,20 @@ static int io_import_umem(struct io_zcrx_ifq *ifq,
 		return ret;
 	}
 
-	mem->account_pages = io_count_account_pages(pages, nr_pages);
-	ret = io_account_mem(ifq->user, ifq->mm_account, mem->account_pages);
-	if (ret < 0)
-		mem->account_pages = 0;
-
 	mem->sgt = &mem->page_sg_table;
 	mem->pages = pages;
 	mem->nr_folios = nr_pages;
 	mem->size = area_reg->len;
-	return ret;
+
+	mem->account_pages = io_count_account_pages(pages, nr_pages);
+	ret = io_account_mem(ifq->user, ifq->mm_account, mem->account_pages);
+	if (ret < 0) {
+		mem->account_pages = 0;
+		io_release_area_mem(mem);
+		return ret;
+	}
+
+	return 0;
 }
 
 static void io_release_area_mem(struct io_zcrx_mem *mem)
@@ -236,6 +242,7 @@ static void io_release_area_mem(struct io_zcrx_mem *mem)
 		sg_free_table(mem->sgt);
 		mem->sgt = NULL;
 		kvfree(mem->pages);
+		mem->pages = NULL;
 	}
 }
 
-- 
2.43.0