4.14-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
commit 0ac1d13a55eb37d398b63e6ff6db4a09a2c9128c upstream.
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 jannh@google.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/send.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/btrfs/send.c +++ b/fs/btrfs/send.c @@ -6680,7 +6680,7 @@ long btrfs_ioctl_send(struct file *mnt_f sctx->flags = arg->flags;
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; }