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btrfs: send: ensure send_fd is writable
commit0ac1d13a55
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 commita01ac27be4
("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:31db9f7c23
("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>
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@ -6680,7 +6680,7 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
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sctx->flags = arg->flags;
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sctx->send_filp = fget(arg->send_fd);
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if (!sctx->send_filp) {
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if (!sctx->send_filp || !(sctx->send_filp->f_mode & FMODE_WRITE)) {
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ret = -EBADF;
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goto out;
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}
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