From 0ac1d13a55eb37d398b63e6ff6db4a09a2c9128c Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Fri, 24 Nov 2023 17:48:31 +0100 Subject: btrfs: send: ensure send_fd is writable kernel_write() requires the caller to ensure that the file is writable. Let's do that directly after looking up the ->send_fd. We don't need a separate bailout path because the "out" path already does fput() if ->send_filp is non-NULL. This has no security impact for two reasons: - the ioctl requires CAP_SYS_ADMIN - __kernel_write() bails out on read-only files - but only since 5.8, see commit a01ac27be472 ("fs: check FMODE_WRITE in __kernel_write") Reported-and-tested-by: syzbot+12e098239d20385264d3@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=12e098239d20385264d3 Fixes: 31db9f7c23fb ("Btrfs: introduce BTRFS_IOC_SEND for btrfs send/receive") CC: stable@vger.kernel.org # 4.14+ Signed-off-by: Jann Horn Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/send.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/btrfs/send.c') diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c index 3b929f0e8f04..4e36550618e5 100644 --- a/fs/btrfs/send.c +++ b/fs/btrfs/send.c @@ -8158,7 +8158,7 @@ long btrfs_ioctl_send(struct inode *inode, struct btrfs_ioctl_send_args *arg) } sctx->send_filp = fget(arg->send_fd); - if (!sctx->send_filp) { + if (!sctx->send_filp || !(sctx->send_filp->f_mode & FMODE_WRITE)) { ret = -EBADF; goto out; } -- cgit