On Fri, Mar 21, 2025 at 3:38 PM Sungjong Seo sj1557.seo@samsung.com wrote:
When get_block is called with a buffer_head allocated on the stack, such as do_mpage_readpage, stack corruption due to buffer_head UAF may occur in the following race condition situation.
<CPU 0> <CPU 1>mpage_read_folio <<bh on stack>> do_mpage_readpage exfat_get_block bh_read __bh_read get_bh(bh) submit_bh wait_on_buffer ... end_buffer_read_sync __end_buffer_read_notouch unlock_buffer <<keep going>> ... ... ... ... <<bh is not valid out of mpage_read_folio>> . . another_function <<variable A on stack>> put_bh(bh) atomic_dec(bh->b_count)
- stack corruption here *
This patch returns -EAGAIN if a folio does not have buffers when bh_read needs to be called. By doing this, the caller can fallback to functions like block_read_full_folio(), create a buffer_head in the folio, and then call get_block again.
Let's do not call bh_read() with on-stack buffer_head.
Fixes: 11a347fb6cef ("exfat: change to get file size from DataLength") Cc: stable@vger.kernel.org Tested-by: Yeongjin Gil youngjin.gil@samsung.com Signed-off-by: Sungjong Seo sj1557.seo@samsung.com
Applied it to #dev. Thanks!