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btrfs: send: ensure send_fd is writable

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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 a01ac27be4 ("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>
This commit is contained in:
Jann Horn 2023-11-24 17:48:31 +01:00 committed by Greg Kroah-Hartman
parent 86742a963f
commit 4fc9c61c02
1 changed files with 1 additions and 1 deletions
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2
fs/btrfs/send.c
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@ -7885,7 +7885,7 @@ 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;
}