tree 77291bd4eac2d16d5a5158ba95c19f7ce669b565
parent 0d02ec6b3136c73c09e7859f0d0e4e2c4c07b49b
author Christian Brauner <christian.brauner@ubuntu.com> 1617352176 +0200
committer Christian Brauner <christian.brauner@ubuntu.com> 1617365470 +0200
gpgsig -----BEGIN PGP SIGNATURE-----
 
 iHUEABYKAB0WIQRAhzRXHqcMeLMyaSiRxhvAZXjcogUCYGcJ3gAKCRCRxhvAZXjc
 og19APoDsAU/Z2J/YKHvANLFEAt3mYBKjhZ7dq3B03nBHoEGEAEA374hWMUeK3PS
 jrvdmJ40DdkH+cnTY4aFmDyIxxn+rgo=
 =XEQl
 -----END PGP SIGNATURE-----

file: fix close_range() for unshare+cloexec

syzbot reported a bug when putting the last reference to a tasks file
descriptor table. Debugging this showed we didn't recalculate the
current maximum fd number for CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC
after we unshared the file descriptors table. So max_fd could exceed the
current fdtable maximum causing us to set excessive bits. As a concrete
example, let's say the user requested everything from fd 4 to ~0UL to be
closed and their current fdtable size is 256 with their highest open fd
being 4. With CLOSE_RANGE_UNSHARE the caller will end up with a new
fdtable which has room for 64 file descriptors since that is the lowest
fdtable size we accept. But now max_fd will still point to 255 and needs
to be adjusted. Fix this by retrieving the correct maximum fd value in
__range_cloexec().

Reported-by: syzbot+283ce5a46486d6acdbaf@syzkaller.appspotmail.com
Fixes: 582f1fb6b721 ("fs, close_range: add flag CLOSE_RANGE_CLOEXEC")
Fixes: fec8a6a69103 ("close_range: unshare all fds for CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Giuseppe Scrivano <gscrivan@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>