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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-486f4b74abdsm41889235e9.5.2026.03.18.11.27.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 11:27:03 -0700 (PDT) From: David Carlier To: Miklos Szeredi Cc: linux-fsdevel@vger.kernel.org, David Carlier Subject: [PATCH] fuse: add missing NULL check for fget() in fuse_parse_param() Date: Wed, 18 Mar 2026 18:27:01 +0000 Message-ID: <20260318182701.21697-1-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In the OPT_FD case of fuse_parse_param(), when using the old mount API, fget() is called on the user-supplied file descriptor but its return value is not checked for NULL before being passed to fuse_opt_fd(). fuse_opt_fd() unconditionally dereferences file->f_op, causing a kernel NULL pointer dereference. This is user-triggerable via: mount -t fuse -o fd=99999 dummy /mnt where fd 99999 is not open. The new mount API path (FSCONFIG_SET_FD) is not affected because fsopen.c validates the fd with fget_raw() + NULL check before setting param->file. Add a NULL check after fget() and return an error via invalfc() when the fd is invalid. Fixes: 3f2496deff35 ("fuse: don't require /dev/fuse fd to be kept open during mount") Signed-off-by: David Carlier --- fs/fuse/inode.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c index af8ad96829fd..39b635651165 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -862,6 +862,8 @@ static int fuse_parse_param(struct fs_context *fsc, struct fs_parameter *param) return fuse_opt_fd(fsc, param->file); } else { struct file *file __free(fput) = fget(result.uint_32); + if (!file) + return invalfc(fsc, "Invalid fuse fd"); return fuse_opt_fd(fsc, file); } -- 2.53.0