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ring-buffer: Make reading page consistent with the code logic

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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>
This commit is contained in:
Jeongjun Park
2025-01-11 01:26:12 +09:00
committed by Steven Rostedt (Google)
parent 0568c6ebf0
commit 6e31b759b0
1 changed files with 3 additions and 1 deletions
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4
kernel/trace/ring_buffer.c
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@@ -7028,7 +7028,7 @@ 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)) {
@@ -7036,6 +7036,8 @@ 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;