erofs: fix out-of-bound access when z_erofs_gbuf_growsize() partially fails

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: erofs: fix out-of-bound access when z_erofs_gbuf_growsize() partially fails If z_erofs_gbuf_growsize() partially fails on a global buffer due to memory allocation failure or fault injection (as reported by syzbot [1]), new pages need to be freed by comparing to the existing pages to avoid memory leaks. However, the old gbuf->pages[] array may not be large enough, which can lead to null-ptr-deref or out-of-bound access. Fix this by checking against gbuf->nrpages in advance. [1] https://lore.kernel.org/r/000000000000f7b96e062018c6e3@google.com

References

• https://git.kernel.org/stable/c/49c0e081998008cde0c872c0ff9affa1ece4b878
• https://git.kernel.org/stable/c/0005e01e1e875c5e27130c5e2ed0189749d1e08a