Use After Free Affecting kernel package, versions <0:4.14.262-200.489.amzn2

Note: Versions mentioned in the description apply only to the upstream kernel package and not the kernel package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2 relevant fixed versions and status.

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

net/mlx4_en: Fix an use-after-free bug in mlx4_en_try_alloc_resources()

In mlx4_en_try_alloc_resources(), mlx4_en_copy_priv() is called and tmp->tx_cq will be freed on the error path of mlx4_en_copy_priv(). After that mlx4_en_alloc_resources() is called and there is a dereference of &tmp->tx_cq[t][i] in mlx4_en_alloc_resources(), which could lead to a use after free problem on failure of mlx4_en_copy_priv().

Fix this bug by adding a check of mlx4_en_copy_priv()

This bug was found by a static analyzer. The analysis employs differential checking to identify inconsistent security operations (e.g., checks or kfrees) between two code paths and confirms that the inconsistent operations are not recovered in the current function or the callers, so they constitute bugs.

Note that, as a bug found by static analysis, it can be a false positive or hard to trigger. Multiple researchers have cross-reviewed the bug.

Builds with CONFIG_MLX4_EN=m show no new warnings, and our static analyzer no longer warns about this code.

• http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-47541
• https://git.kernel.org/stable/c/676dc7d9b15bf8733233a2db1ec3f9091ab34275
• https://git.kernel.org/stable/c/75917372eef0dbfb290ae45474314d35f97aea18
• https://git.kernel.org/stable/c/addad7643142f500080417dd7272f49b7a185570
• https://git.kernel.org/stable/c/be12572c5ddc8ad7453bada4eec8fa46967dc757
• https://git.kernel.org/stable/c/e461a9816a1ac5b4aeb61621b817225b61e46a68
• https://git.kernel.org/stable/c/f1d43efa59f1edd3e7eca0e94559b4c6b1cd4e2b