CVE-2022-49464

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

erofs: fix buffer copy overflow of ztailpacking feature

I got some KASAN report as below:

[ 46.959738] ================================================================== [ 46.960430] BUG: KASAN: use-after-free in z_erofs_shifted_transform+0x2bd/0x370 [ 46.960430] Read of size 4074 at addr ffff8880300c2f8e by task fssum/188 … [ 46.960430] Call Trace: [ 46.960430] [ 46.960430] dump_stack_lvl+0x41/0x5e [ 46.960430] print_report.cold+0xb2/0x6b7 [ 46.960430] ? z_erofs_shifted_transform+0x2bd/0x370 [ 46.960430] kasan_report+0x8a/0x140 [ 46.960430] ? z_erofs_shifted_transform+0x2bd/0x370 [ 46.960430] kasan_check_range+0x14d/0x1d0 [ 46.960430] memcpy+0x20/0x60 [ 46.960430] z_erofs_shifted_transform+0x2bd/0x370 [ 46.960430] z_erofs_decompress_pcluster+0xaae/0x1080

The root cause is that the tail pcluster wont be a complete filesystem block anymore. So if ztailpacking is used, the second part of an uncompressed tail pcluster may not be rq->pageofs_out.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/4d53a625f29074e7b8236c2c0e0922edb7608df9
• https://git.kernel.org/stable/c/6b59e1907f58cf877c563dcf013159eb9f994b64
• https://git.kernel.org/stable/c/dcbe6803fffd387f72b48c2373b5f5ed12a5804b