zram: fix use-after-free in zram_bvec_write_partial()
In the Linux kernel, the following vulnerability has been resolved:
zram: fix use-after-free in zram_bvec_write_partial()
zram_read_page() picks the sync or async backing device read path based on
whether the parent bio is NULL. zram_bvec_write_partial() passes its
parent bio down, so for ZRAM_WB slots the read is dispatched
asynchronously and zram_read_page() returns 0 while the bio is still in
flight. The caller then runs memcpy_from_bvec(), zram_write_page() and
__free_page() on the buffer, leaving the async read to write into a freed
page.
zram_bvec_read_partial() was switched to NULL in commit 4e3c87b9421d
("zram: fix synchronous reads") for the same reason; the write_partial
counterpart was missed.
kernel: zram: fix use-after-free in zram_bvec_write_partial()
A flaw was found in the Linux kernel, specifically within the zram module. This vulnerability is a use-after-free error, where the system attempts to use a piece of memory after it has been freed. This occurs when the `zram_bvec_write_partial()` function allows an asynchronous read to write into a page that has already been deallocated. Such a flaw can lead to system instability, causing crashes, or in some scenarios, could be exploited by a local attacker to escalate privileges or execute arbitrary code.
To mitigate this issue, prevent module zram from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.