TLDRVuln - Cybersecurity Vulnerabilities Made Simple

In the Linux kernel, the following vulnerability has been resolved:

net: tun: Fix memory leaks of napi_get_frags

kmemleak reports after running test_progs:

unreferenced object 0xffff8881b1672dc0 (size 232):

comm "test_progs", pid 394388, jiffies 4354712116 (age 841.975s)

hex dump (first 32 bytes):

e0 84 d7 a8 81 88 ff ff 80 2c 67 b1 81 88 ff ff .........,g.....

00 40 c5 9b 81 88 ff ff 00 00 00 00 00 00 00 00 .@..............

backtrace:

[<00000000c8f01748>] napi_skb_cache_get+0xd4/0x150

[<0000000041c7fc09>] __napi_build_skb+0x15/0x50

[<00000000431c7079>] __napi_alloc_skb+0x26e/0x540

[<000000003ecfa30e>] napi_get_frags+0x59/0x140

[<0000000099b2199e>] tun_get_user+0x183d/0x3bb0 [tun]

[<000000008a5adef0>] tun_chr_write_iter+0xc0/0x1b1 [tun]

[<0000000049993ff4>] do_iter_readv_writev+0x19f/0x320

[<000000008f338ea2>] do_iter_write+0x135/0x630

[<000000008a3377a4>] vfs_writev+0x12e/0x440

[<00000000a6b5639a>] do_writev+0x104/0x280

[<00000000ccf065d8>] do_syscall_64+0x3b/0x90

[<00000000d776e329>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

The issue occurs in the following scenarios:

tun_get_user()

napi_gro_frags()

napi_frags_finish()

case GRO_NORMAL:

gro_normal_one()

list_add_tail(&skb->list, &napi->rx_list);

<-- While napi->rx_count < READ_ONCE(gro_normal_batch),

<-- gro_normal_list() is not called, napi->rx_list is not empty

<-- not ask to complete the gro work, will cause memory leaks in

<-- following tun_napi_del()

...

tun_napi_del()

netif_napi_del()

__netif_napi_del()

<-- &napi->rx_list is not empty, which caused memory leaks

To fix, add napi_complete() after napi_gro_frags().