linux-kernel - [PATCH] memfd: Check for non-NULL file_seals in memfd

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Message-Id: <20230607132427.2867435-1-roberto.sassu@huaweicloud.com>
Date:   Wed,  7 Jun 2023 15:24:27 +0200
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>,
        stable@...r.kernel.org
Subject: [PATCH] memfd: Check for non-NULL file_seals in memfd_create() syscall

From: Roberto Sassu <roberto.sassu@...wei.com>

Ensure that file_seals is non-NULL before using it in the memfd_create()
syscall. One situation in which memfd_file_seals_ptr() could return a NULL
pointer is when CONFIG_SHMEM=n.

Cc: stable@...r.kernel.org # 4.16.x
Fixes: 47b9012ecdc7 ("shmem: add sealing support to hugetlb-backed memfd")
Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 mm/memfd.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/memfd.c b/mm/memfd.c
index 69b90c31d38..e763e76f110 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -371,12 +371,15 @@ SYSCALL_DEFINE2(memfd_create,
 
 		inode->i_mode &= ~0111;
 		file_seals = memfd_file_seals_ptr(file);
-		*file_seals &= ~F_SEAL_SEAL;
-		*file_seals |= F_SEAL_EXEC;
+		if (file_seals) {
+			*file_seals &= ~F_SEAL_SEAL;
+			*file_seals |= F_SEAL_EXEC;
+		}
 	} else if (flags & MFD_ALLOW_SEALING) {
 		/* MFD_EXEC and MFD_ALLOW_SEALING are set */
 		file_seals = memfd_file_seals_ptr(file);
-		*file_seals &= ~F_SEAL_SEAL;
+		if (file_seals)
+			*file_seals &= ~F_SEAL_SEAL;
 	}
 
 	fd_install(fd, file);
-- 
2.25.1