Patch "bpf: Fix integer overflow in prealloc_elems_and_freelist()" has been added to the 4.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpf: Fix integer overflow in prealloc_elems_and_freelist()

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-fix-integer-overflow-in-prealloc_elems_and_freel.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 196c53db3b28fce112b3408edb4ea6a470e2e12a
Author: Tatsuhiko Yasumatsu <th.yasumatsu@xxxxxxxxx>
Date:   Thu Sep 30 22:55:45 2021 +0900

    bpf: Fix integer overflow in prealloc_elems_and_freelist()
    
    [ Upstream commit 30e29a9a2bc6a4888335a6ede968b75cd329657a ]
    
    In prealloc_elems_and_freelist(), the multiplication to calculate the
    size passed to bpf_map_area_alloc() could lead to an integer overflow.
    As a result, out-of-bounds write could occur in pcpu_freelist_populate()
    as reported by KASAN:
    
    [...]
    [   16.968613] BUG: KASAN: slab-out-of-bounds in pcpu_freelist_populate+0xd9/0x100
    [   16.969408] Write of size 8 at addr ffff888104fc6ea0 by task crash/78
    [   16.970038]
    [   16.970195] CPU: 0 PID: 78 Comm: crash Not tainted 5.15.0-rc2+ #1
    [   16.970878] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
    [   16.972026] Call Trace:
    [   16.972306]  dump_stack_lvl+0x34/0x44
    [   16.972687]  print_address_description.constprop.0+0x21/0x140
    [   16.973297]  ? pcpu_freelist_populate+0xd9/0x100
    [   16.973777]  ? pcpu_freelist_populate+0xd9/0x100
    [   16.974257]  kasan_report.cold+0x7f/0x11b
    [   16.974681]  ? pcpu_freelist_populate+0xd9/0x100
    [   16.975190]  pcpu_freelist_populate+0xd9/0x100
    [   16.975669]  stack_map_alloc+0x209/0x2a0
    [   16.976106]  __sys_bpf+0xd83/0x2ce0
    [...]
    
    The possibility of this overflow was originally discussed in [0], but
    was overlooked.
    
    Fix the integer overflow by changing elem_size to u64 from u32.
    
      [0] https://lore.kernel.org/bpf/728b238e-a481-eb50-98e9-b0f430ab01e7@xxxxxxxxx/
    
    Fixes: 557c0c6e7df8 ("bpf: convert stackmap to pre-allocation")
    Signed-off-by: Tatsuhiko Yasumatsu <th.yasumatsu@xxxxxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20210930135545.173698-1-th.yasumatsu@xxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 2fdf6f96f976..6f09728cd1dd 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -28,7 +28,8 @@ struct bpf_stack_map {
 
 static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
 {
-	u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
+	u64 elem_size = sizeof(struct stack_map_bucket) +
+			(u64)smap->map.value_size;
 	int err;
 
 	smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries);