From: Jeongjun Park aha310510@gmail.com
[ Upstream commit 6e31b759b076eebb4184117234f0c4eb9e4bc460 ]
In the loop of __rb_map_vma(), the 's' variable is calculated from the same logic that nr_pages is and they both come from nr_subbufs. But the relationship is not obvious and there's a WARN_ON_ONCE() around the 's' variable to make sure it never becomes equal to nr_subbufs within the loop. If that happens, then the code is buggy and needs to be fixed.
The 'page' variable is calculated from cpu_buffer->subbuf_ids[s] which is an array of 'nr_subbufs' entries. If the code becomes buggy and 's' becomes equal to or greater than 'nr_subbufs' then this will be an out of bounds hit before the WARN_ON() is triggered and the code exiting safely.
Make the 'page' initialization consistent with the code logic and assign it after the out of bounds check.
Link: https://lore.kernel.org/20250110162612.13983-1-aha310510@gmail.com Signed-off-by: Jeongjun Park aha310510@gmail.com [ sdr: rewrote change log ] Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/trace/ring_buffer.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 703978b2d557d..28fad7bcfcf86 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -7059,7 +7059,7 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, }
while (p < nr_pages) { - struct page *page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]); + struct page *page; int off = 0;
if (WARN_ON_ONCE(s >= nr_subbufs)) { @@ -7067,6 +7067,8 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, goto out; }
+ page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]); + for (; off < (1 << (subbuf_order)); off++, page++) { if (p >= nr_pages) break;