CVE-2022-49871

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().

Weakness

The product does not sufficiently track and release allocated memory after it has been used, which slowly consumes remaining memory.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/1118b2049d77ca0b505775fc1a8d1909cf19a7ec
• https://git.kernel.org/stable/c/223ef6a94e52331a6a7ef31e59921e0e82d2d40a
• https://git.kernel.org/stable/c/3401f964028ac941425b9b2c8ff8a022539ef44a
• https://git.kernel.org/stable/c/8b12a020b20a78f62bedc50f26db3bf4fadf8cb9
• https://git.kernel.org/stable/c/a4f73f6adc53fd7a3f9771cbc89a03ef39b0b755
• https://git.kernel.org/stable/c/d7569302a7a52a9305d2fb054df908ff985553bb