nilfs2: fix null-ptr-deref in block_touch_buffer tracepoint

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nilfs2: fix null-ptr-deref in block_touch_buffer tracepoint Patch series "nilfs2: fix null-ptr-deref bugs on block tracepoints". This series fixes null pointer dereference bugs that occur when using nilfs2 and two block-related tracepoints. This patch (of 2): It has been reported that when using "block:block_touch_buffer" tracepoint, touch_buffer() called from __nilfs_get_folio_block() causes a NULL pointer dereference, or a general protection fault when KASAN is enabled. This happens because since the tracepoint was added in touch_buffer(), it references the dev_t member bh->b_bdev->bd_dev regardless of whether the buffer head has a pointer to a block_device structure. In the current implementation, the block_device structure is set after the function returns to the caller. Here, touch_buffer() is used to mark the folio/page that owns the buffer head as accessed, but the common search helper for folio/page used by the caller function was optimized to mark the folio/page as accessed when it was reimplemented a long time ago, eliminating the need to call touch_buffer() here in the first place. So this solves the issue by eliminating the touch_buffer() call itself.

References

• https://git.kernel.org/stable/c/085556bf8c70e2629e02e79268dac3016a08b8bf
• https://git.kernel.org/stable/c/6438f3f42cda825f6f59b4e45ac3a1da28a6f2c9
• https://git.kernel.org/stable/c/b017697a517f8779ada4e8ce1c2c75dbf60a2636
• https://git.kernel.org/stable/c/19c71cdd77973f99a9adc3190130bc3aa7ae5423
• https://git.kernel.org/stable/c/3b2a4fd9bbee77afdd3ed5a05a0c02b6cde8d3b9
• https://git.kernel.org/stable/c/59b49ca67cca7b007a5afd3de0283c8008157665
• https://git.kernel.org/stable/c/77e47f89d32c2d72eb33d0becbce7abe14d061f4
• https://git.kernel.org/stable/c/cd45e963e44b0f10d90b9e6c0e8b4f47f3c92471