Commit eaa2f87c authored Aug 18, 2017 by Dan Carpenter Committed by Ingo Molnar Aug 29, 2017

x86/ldt: Fix off by one in get_segment_base()



ldt->entries[] is allocated in alloc_ldt_struct().  It has
ldt->nr_entries elements and ldt->nr_entries is capped at LDT_ENTRIES.
So if "idx" is == ldt->nr_entries then we're reading beyond the end of
the buffer.  It seems duplicative to have two limit checks when one
would work just as well so I removed the check against LDT_ENTRIES.

The gdt_page.gdt[] array has GDT_ENTRIES entries.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-janitors@vger.kernel.org
Fixes: d07bdfd3 ("perf/x86: Fix USER/KERNEL tagging of samples properly")
Link: http://lkml.kernel.org/r/20170818102516.gqwm4xdvvuvjw5ho@mwanda


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 9c3a815f

arch/x86/events/core.c

+2 −5

Original line number	Diff line number	Diff line
		@@ -2335,12 +2335,9 @@ static unsigned long get_segment_base(unsigned int segment)
		#ifdef CONFIG_MODIFY_LDT_SYSCALL
		struct ldt_struct *ldt;

		if (idx > LDT_ENTRIES)
		return 0;

		/* IRQs are off, so this synchronizes with smp_store_release */
		ldt = lockless_dereference(current->active_mm->context.ldt);
		if (!ldt \|\| idx > ldt->nr_entries)
		if (!ldt \|\| idx >= ldt->nr_entries)
		return 0;

		desc = &ldt->entries[idx];
		@@ -2348,7 +2345,7 @@ static unsigned long get_segment_base(unsigned int segment)
		return 0;
		#endif
		} else {
		if (idx > GDT_ENTRIES)
		if (idx >= GDT_ENTRIES)
		return 0;

		desc = raw_cpu_ptr(gdt_page.gdt) + idx;

Admin message