| Message ID | 20231124164831.2191549-1-jannh@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: send: Ensure send_fd is writable | expand |
On Fri, Nov 24, 2023 at 05:48:31PM +0100, Jann Horn wrote: > 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 > Signed-off-by: Jann Horn <jannh@google.com> Added to misc-next, thanks.
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; }
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 Signed-off-by: Jann Horn <jannh@google.com> --- fs/btrfs/send.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) base-commit: 98b1cc82c4affc16f5598d4fa14b1858671b2263