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Passing a maximum attribute type to nlmsg_parse() that is larger than the size of the passed policy will result in an out-of-bounds access [1] when the attribute type is used as an index into the policy array. Fix by setting the maximum attribute type according to the policy size, as is already done for RTM_NEWNEXTHOP messages. Add a test case that triggers the bug. No regressions in fib nexthops tests: # ./fib_nexthops.sh [...] Tests passed: 236 Tests failed: 0 [1] BUG: KASAN: global-out-of-bounds in __nla_validate_parse+0x1e53/0x2940 Read of size 1 at addr ffffffff99ab4d20 by task ip/610 CPU: 3 PID: 610 Comm: ip Not tainted 6.8.0-rc7-custom-gd435d6e3e161 #9 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc38 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x8f/0xe0 print_report+0xcf/0x670 kasan_report+0xd8/0x110 __nla_validate_parse+0x1e53/0x2940 __nla_parse+0x40/0x50 rtm_del_nexthop+0x1bd/0x400 rtnetlink_rcv_msg+0x3cc/0xf20 netlink_rcv_skb+0x170/0x440 netlink_unicast+0x540/0x820 netlink_sendmsg+0x8d3/0xdb0 ____sys_sendmsg+0x31f/0xa60 ___sys_sendmsg+0x13a/0x1e0 __sys_sendmsg+0x11c/0x1f0 do_syscall_64+0xc5/0x1d0 entry_SYSCALL_64_after_hwframe+0x63/0x6b [...] The buggy address belongs to the variable: rtm_nh_policy_del+0x20/0x40 Fixes: 2118f9390d83 ("net: nexthop: Adjust netlink policy parsing for a new attribute") Reported-by: Eric Dumazet <edumazet@google.com> Closes: https://lore.kernel.org/netdev/CANn89i+UNcG0PJMW5X7gOMunF38ryMh=L1aeZUKH3kL4UdUqag@mail.gmail.com/ Reported-by: syzbot+65bb09a7208ce3d4a633@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/00000000000088981b06133bc07b@google.com/ Signed-off-by: Ido Schimmel <idosch@nvidia.com> Reviewed-by: David Ahern <dsahern@kernel.org> Link: https://lore.kernel.org/r/20240311162307.545385-4-idosch@nvidia.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.